BUILDING TECHNOLOGIES PROGRAM

Energy Renovations

HVAC

A Guide for Contractors to Share 

with Homeowners

PREPARED BY

Pacific Northwest National Laboratory 

& Oak Ridge National Laboratory

August 2011

August 2011 • PNNL-20421

VOLUME 14. BUILDING AMERICA BEST PRACTICES SERIES

R

BUILDING AMERICA BEST PRACTICES SERIES

Energy Renovations

Volume 14: HVAC

A Guide for Contractors to Share with Homeowners

Prepared by

Pacific Northwest National Laboratory

Program Manager: Michael C. Baechler 

Theresa L. Gilbride, Michael C. Baechler, Marye G. Hefty, 

and James R. Hand

and 

Oak Ridge National Laboratory 

Pat M. Love

August 2011

Prepared for the 

U.S. Department of Energy Building America Program

PNNL-20421

Pacific Northwest National Laboratory

Richland, Washington 99352

Contract DE-AC05-76RLO 1830

This report was prepared as an account of work sponsored by an agency of the 

United States Government. Neither the United States Government nor any agency 

thereof, nor Battelle Memorial Institute, nor any of their employees, makes any 

warranty, express or implied, or assumes any legal liability or responsibility for the 

accuracy, completeness, or usefulness of any information, apparatus, product, or 

process disclosed, or represents that its use would not infringe privately owned rights. 

Reference herein to any specific commercial product, process, or service by trade 

name, trademark, manufacturer, or otherwise does not necessarily constitute or imply 

its endorsement, recommendation, or favoring by the United States Government or 

any agency thereof, or Battelle Memorial Institute. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States 

Government or any agency thereof.

Preface

Research conducted by the U.S. Department of Energy (DOE) has 

shown that Americans can significantly improve the energy efficiency, 

safety, and comfort of their homes while reducing emissions and 

utility bills. Studies show that upgrading a home’s heating and 

cooling equipment can reduce energy use by up to 20% or more, 

depending on the condition of the existing systems. Similar savings 

may be realized by improving the distribution efficiency of the 

heating and cooling systems. 

This guide, which is part of a series of Best Practices guides produced 

by DOE’s Building America program, describes ways homeowners 

can reduce their energy costs and improve the comfort, health, and 

safety of their homes by upgrading their heating, ventilation, and 

air conditioning (HVAC) equipment. A variety of types of heating 

and cooling equipment are described. The references throughout this 

document provide additional information about important aspects 

of residential HVAC.

The recommendations provided here are primarily based on the 

results of research and demonstration projects conducted by DOE’s 

Building America research teams. Building America collaborates 

with building scientists, researchers, and more than 300 home 

builders across the country with the goal of constructing homes that 

are safer and more energy-efficient, comfortable, and durable, with 

low or no additional cost.

Much of the information in the ventilation chapter was drawn from 

work prepared by Armin Rudd of Building Science Corporation, 

one of the Building America research teams. All photographs and 

figures in this report were prepared by Pacific Northwest National 

Laboratory (PNNL) unless otherwise noted. 

R

You can learn more about Building 

America and download additional copies 

of this document, other best practices, 

research reports, and case studies at www.

buildingamerica.gov

Go to http://www1.eere.energy.gov/

buildings/building_america/research_

teams.html to view the current list of 

Building America teams.

August 2011 i

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ENERGY RENOVATIONS HVAC
Contents

Preface ................................................................................................................. i

1.0 Introduction.................................................................................................1

1.1 Building America’s Whole-House Approach ........................1

1.2 The Home Performance Energy Assessment ......................2

1.3 Space Heating and Cooling........................................................3

1.4 Building Permits and Codes .......................................................3

2.0 Heating Systems ......................................................................................5

2.1 Furnaces ............................................................................................8

2.1.1 Furnace Efficiency ..............................................................8

2.1.2 Repair or Replace?............................................................10

2.1.3 Ducts .....................................................................................12

2.2 Electric Heaters .............................................................................15

2.2.1 Electric Central Furnaces ...............................................15

2.2.2 Room Heaters ....................................................................15

2.2.3 Zoning....................................................................................16

2.3 Heat Pumps.....................................................................................17

2.3.1 Central Air-Source Heat Pumps.....................................18

2.3.2 Ductless Heat Pumps........................................................19

2.3.3 Ground-Source Heat Pumps.........................................20

2.4 Boilers and Hydronic Heating................................................. 23

2.4.1 Steam and Hot Water Radiators ................................ 23

2.4.2 Radiant Floor Heating ....................................................24

2.4.3 Repair or Replace.............................................................24

2.5 Wood and Pellet Heating.......................................................... 25

2.6 Solar Heating.................................................................................26

2.6.1 Passive Solar Heating....................................................... 27

2.6.2 Active Solar Heating........................................................28

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ENERGY RENOVATIONS HVAC
3.0 Cooling Systems ..................................................................................29

3.1 Central Air Conditioning ..........................................................33

3.1.1 Repair or Replace?...........................................................34

3.2. Room Air Conditioning..............................................................36

3.3 Heat Pumps ..................................................................................36

3.3.1 Central- and Ground-Source Heat Pumps..............36

3.3.2 Ductless Heat Pumps......................................................36

3.3.3 Absorption Heat Pumps ................................................ 37

3.4 Evaporative Coolers....................................................................38

3.5 Radiant Cooling............................................................................39

3.6 Dehumidifiers .............................................................................. 40

3.7 Natural Cooling Strategies .......................................................41

3.7.1 Fans and Ventilation for Cooling.................................41

3.7.2 Passive Cooling ................................................................44

4.0 Ventilation...............................................................................................47

4.1 Exhaust-Only Ventilation..........................................................49

4.2 Supply-Only Ventilation ...........................................................50

4.3 Balanced Systems......................................................................... 51

4.4 “Semi-Balanced” System............................................................. 51

5.0 The Home Performance Energy Assessment ............................ 53

5.1 Certified Energy Contractors.................................................... 53

5.2 The Energy Assessment Process.............................................54

5.2.1 Step 1. The Energy Performance Assessment ......54

5.2.2 Step 2. Making Energy-Efficiency Upgrades .........55

5.2.3 Step 3. Testing Out ..........................................................55

References .....................................................................................................56

Definitions .....................................................................................................58

Building America Teams............................................................................59

August 2011 iii

iii

ENERGY RENOVATIONS HVAC

1.0 Introduction

For the average American homeowner, heating and cooling accounts 

for 40% of annual energy usage (DOE Building Energy Data Book 

2009). Picking the right heating and cooling equipment can reduce 

this significant portion of your utility bill.

This guide provides information about energy-efficient heating, 

ventilation, and cooling (HVAC) equipment options to help 

homeowners cut their energy use, reduce their carbon footprint, and 

increase their homes’ comfort, health, and safety. This guide will help 

you make informed decisions about purchasing new HVAC equipment 

or improving existing equipment for more efficient operation. 

If you are a homeowner, use this guide to learn more about energyefficient options in HVAC equipment. If you are a contractor, share 

this guide with your customers.

1.1 Building America’s Whole-House 

Approach

HVAC energy upgrades can improve the energy efficiency, air 

quality, and comfort of your home, and can save money in 

the long term. However, it is important to recognize that each 

component of the HVAC system interacts with the rest of the 

house. Changing one component—for example upgrading heating 

or cooling equipment, adding ventilation, increasing insulation or 

air sealing—without taking into account these system interactions 

could result in safety issues. 

To ensure health and safety, your HVAC options should be 

considered within a whole-house, systems-based approach advocated 

by the U.S. Department of Energy Building America program and 

The best practices and 

recommendations in this guide are 

based on years of building science 

research by the U.S. Department of 

Energy’s (DOE) Building America 

and its 15 teams of building science 

researchers. These Building America 

teams collaborate with building 

scientists, industry partners, and 

researchers, and more than 300 home 

builders across the country with the 

goal of constructing and renovating 

more energy-efficient, comfortable, 

and durable homes. Building America’s 

work has directly influenced the 

performance of more than 42,000 new 

and retrofitted homes to date.

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August 2011 1

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ENERGY RENOVATIONS HVAC
building scientists across the country. This whole-house approach, 

which is based on years of research in thousands of real homes, 

takes into account how one change in a home’s HVAC system can 

affect the energy efficiency, comfort, durability, health, and safety of 

the whole house.

To implement this whole-house approach and and to confirm real 

energy-use improvements, Building America recommends that 

HVAC home energy upgrades start with a home performance 

energy assessment.

1.2 The Home Performance Energy 

Assessment

The home energy assessment is conducted within the context of 

a whole-house system-based approach to home performance to 

ensure homeowner health and safety as well as energy performance. 

The home energy assessment should be conducted by a contractor 

who is trained in building science principles, such as those described 

in the DOE Guidelines for Home Energy Upgrade Professionals

and the U.S. Environmental Protection Agency’s Healthy Indoor 

Environment Protocols for Home Energy Upgrades, as well as those 

recommended by Home Performance with ENERGY STAR, the 

Building Performance Institute (BPI) standards, state weatherization 

programs, or accredited college program recommendations.

The assessment (also known as an audit) consists of three steps: 

testing in, conducting the work, and testing out. In the test-in 

step, the contractor interviews homeowners about any concerns 

they have about their HVAC system, such as comfort complaints 

or high utility bills; conducts safety tests and tests for air leakage 

in the ducts and whole house; and visually inspects for insulation 

levels and signs of mold or moisture problems. The contractor 

uses energy software to analyze the results and gives this report to 

the homeowner, along with a prioritized list of recommendations. 

The homeowner works with the energy performance contractor or 

HVAC contractor to determine a scope of work and have the work 

completed. In the test-out step, the completed work is evaluated with 

safety tests and visual inspections.

For more information on what you can learn from a home 

performance energy assessment and why it is a good idea to have 

one, see Chapter 5 of this report.

How to find a certified 

energy contractor

An easy way to find a certified energy 

contractor is through a national or 

regional retrofit program. One such 

program is Home Performance with 

ENERGY STAR, a national program 

from the U.S. Environmental Protection 

Agency and the U.S. Department of 

Energy that is applied at the state 

level. Go to www.energystar.gov and 

click on the link for Home Performance 

with ENERGY STAR. Next, click on the 

“locations” link for certified contractors 

in your state. You can also find local 

contractors who understand the wholehouse approach through the Building 

Performance Institute, www.bpi.org, 

and the Residential Energy Services 

Network, www.resnet.us. The Air 

Conditioning Contractors of America 

website has a list of members at www.

acca.org. ACCA produced a checklist 

homeowners can use to evaluate HVAC 

contractors' bid proposals (ACCA 

2011a). North American Technician 

Excellence (NATE) also certifies HVAC 

contractors (www.hvacadvice.com).

An energy contractor can help you 

evaluate the best options for replacing 

or upgrading your home’s heating and 

cooling equipment.

2 August 2011

ENERGY RENOVATIONS HVAC
1.3 Space Heating and Cooling

Replacing or upgrading your HVAC system offers excellent 

opportunities for cutting your utility bills and improving your home’s 

indoor air quality, comfort, and durability. Your certified energy 

contractor or HVAC contractor can help you determine which 

heating and cooling options are right for you. Talk to your contractor 

about fuel types and prices in your region. Your contractor can help 

you determine whether it is safe and cost-effective to repair and 

improve the HVAC equipment you already have or to replace or 

supplement it with new, more efficient equipment. 

The contractor can also provide advice about other ways to improve 

the energy efficiency of your home, such as by sealing air leaks and 

adding insulation. These efficiency improvements are often the most 

cost-effective means of saving energy in the long run.

If you decide to replace an existing heating or cooling system, one 

option is to replace the existing equipment with an updated model 

of the same type, especially if the distribution system (ducts or 

radiators) is still good. However, this may not be the most efficient 

heating and cooling option for your money. 

See the following chapters for information and recommendations on 

the many heating, cooling, and ventilation options available today.

1.4 Building Permits and Codes

Your contractor will check with your local building department 

to determine what building codes apply and to obtain any needed 

permits. Depending on the extent of your project, you may need a 

building permit and plumbing, electrical, or mechanical permits. 

State or local building codes, including health, safety, and energy 

codes, may apply to building alterations and additions. 

Your local utilities are a good resource for equipment incentives, 

rebates, and low-interest loan programs, as well as listings of local 

licensed contractors and details on any utility requirements that 

might affect your project. Underwriters Laboratory is responsible for 

third-party testing of HVAC equipment, so look for the Underwriters 

Laboratory seal when purchasing equipment (ANSI 2011).

Federal, State, and Utility 

Incentive Programs 

Many local, state, and federal entities 

offer grants and tax credits for 

energy-efficient home improvements. 

Check with your local utility or city, or 

check the DOE-sponsored Database 

of State Incentives for Renewables and 

Efficiency (DSIRE) at www.dsireusa.org. 

This site is frequently updated and 

is a wealth of information, organized 

by state, regarding state, local, utility, 

and federal incentives, tax credits, 

and rebates for renewable energy and 

energy-efficiency upgrades.

 Space heat

 Water heat

 Space coo

 Lighting 9%

 Refrigerati

 Clothes wa

 dryers and 

 Electronics 

 Cooking 3%

 Computer 

 Other 18%

 (includes s

 heating ele

 motors, sw

 hot tub he

 outdoor gr

 Space heating 30%

 Water heating 17%

 Space cooling 10%

 Lighting 9%

 Refrigeration 6%

 Clothes washers, 

 dryers and dishwashers 5%

 Electronics 5%

 Cooking 3%

 Computer 1%

 Other 18%

 (includes small electronics, 

 heating elements, 

 motors, swimming pool and 

 hot tub heaters, 

 outdoor grills) 

HOW THE TYPICAL U.S. 

HOMEOWNER'S ENERGY BILL 

GETS DIVIDED (Source: DOE Building 

Energy Data Book 2009)

August 2011 3

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ENERGY RENOVATIONS HVAC
4 August 2011

ENERGY RENOVATIONS HVAC
Heating Fuel Costs 

Costs for heating oil and natural gas 

have varied greatly in recent years. 

For an apples-to-apples comparison 

of heating types by cost and percent 

efficiency, see the Heating Fuel 

Comparison Calculator developed 

by the U.S. DOE Energy Information 

Administration (EIA). Fuel costs are 

tied to databases that update weekly or 

daily (www.eia.doe.gov/neic/experts/

heatcalc.xls).

2.0 Heating Systems

A variety of technologies are available for heating your house; each 

of these is described in more detail in this chapter; they are listed 

here, in the sections below, from most to least common (EIA 2005).

FURNACES – Furnaces are the most common way to heat a home; 

65% of single-family homes in the United States have a central 

forced-air furnace that distributes heated air throughout the house 

via ducts. More than two-thirds of these are fueled by natural gas; 

other heat sources are electricity, oil, and propane.

ELECTRIC HEATING – Not including heat pumps, 14% of singlefamily homes are heated with electric resistance heat; most are 

central forced-air electric furnaces, but many homes use electric 

space heating, either wall-mounted or baseboard, as their main heat 

source. 

HEAT PUMPS – 10% of U.S. homes use heat pumps. These systems 

can be air-source or ground-source, and are ducted or ductless.

BOILERS – Boilers are used for heating in 8% of U.S. homes. Boilers 

use natural gas, oil, electricity, or propane to heat water for steam or 

hot water that is distributed via pipes to upright radiators, baseboard 

convectors, or radiant floor tubing. Combination units can provide 

space and water heating.

WOOD AND PELLET-FUEL STOVES – These provide a way to 

heat your home using biomass or waste sources and are a primary 

heat source for 3.5% of single-family homes.

SOLAR – Active solar heating uses the sun to heat air that is then 

ducted or blown into living space. Less than 0.4% of homes have 

active solar heating. Solar water heaters can preheat water for 

radiators or radiant floor heat.

$

The National Renewable Energy 

Laboratory has created a database 

of purchase and installation costs for 

heating and cooling equipment and 

energy-efficiency upgrades (http://

www.nrel.gov/ap/retrofits/group_

listing.cfm.)

Look for the ENERGY STAR label when 

you shop for HVAC equipment and 

other home appliances to find products 

that meet high energy-efficiency and 

performance criteria.

How Much Does it Cost?

August 2011 5

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ENERGY RENOVATIONS HVAC
These heating types are described in the next sections. Decisions about repair or replacement are influenced by 

many factors that your contractor can help you evaluate in the context of whole-house performance.

Yes

No

Should I replace my existing heating system?

No Yes

Yes

Consider home improvements like 

insulation and air sealing.

No

Yes

Replace

Is the system 

broken?

Is the system very inefficient?

(Draft-hood equipped gas furnace, 

AFUE <80%; <80% AFUE oil boiler; 

all-electric resistance heat)

Is the system 

over 15 years old? Will repairs cost more 

than half 

the cost of replacement?

No

Repair

Replace

Figure 2.1. Basic Decisions for Replacing your Heating System

6 August 2011

ENERGY RENOVATIONS HVAC
Table 2.1. Common Heating System Options

Fuel Type

Installed 

Cost*

Ducts 

or No 

Ducts

Central 

or Room 

Heating

Best 

Climates

Minimum 

Federal 

Efficiency 

Requirement

Expected 

Efficiency 

of HighPerforming 

Models

ENERGY STAR 

Version 3.0 

Minimum 

Efficiency**

CEE 

Minimum Efficiency

Furnace

Natural 

Gas, 

Fuel Oil, 

Propane

MediumHighDucts Central ModerateCold78% AFUE 90% - 98%

 AFUE

Gas: 

80% AFUE CZ 1-3; 

90% AFUE CZ 4-8 

Oil: 

80% AFUE CZ 1-3; 

85% AFUE CZ 4-8

Tier 1: 90% AFUE

Tier 2: 92% AFUE

Tier 3: 94% AFUE

Electric 

Resistance

Electricity Low Either Either WarmHot-- 100% NA

Air-Source 

Heat Pump

Electricity MediumHighDucts Central ModerateWarm7.7 HSPF 10-12 HSPF,

 200+%

8.2 HSPF CZ 1-3; 

8.5 HSPF CZ 4; 

9.25 HSPF CZ 5; 

9.5 HSPF CZ 6***

Tier 1: 8.5 HSPF

Tier 2:_ 8.5 HSPF >

GroundSource Heat 

Pump

Electricity Very 

High

Ducts Central All 7.7 HSPF 2.3-5 COP,

 300+%

ENERGY STAR 

Qualified Models

Closed-loop 3.3 COP; 

Open-loop 3.6 COP; 

Direct Expansion 

 3.5 COP; 

With Desuperheater

Ductless 

Mini-split 

Heat Pump

Electricity MediumHighNo 

Ducts

Room 

Heating

All 7.7 HSPF 10-12 HSPF 8.2 HSPF CZ 1-3; 

8.5 HSPF CZ 4; 

9.25 HSPF CZ 5; 

9.5 HSPF CZ 6***

Tier 1: 8.5 HSPF

Tier 2: 9.0 HSPF

Boiler

Natural 

Gas, 

Fuel Oil, 

Propane

High No 

Ducts

Central Cold 75% AFUE

 steam, 

80% AFUE 

 hot water

90%-95%

 AFUE

80% AFUE CZ 1-3; 

85% AFUE CZ 4-8

Tier 1: 85% AFUE

Wood, 

Pellet

Wood, 

Pellet

LowHighNo 

ducts

Room 

Heating

All Varies 72% to 90% 75% --

*Estimated typical installed cost ranges for retrofits. These estimates do not include adding or repairing distribution systems. 

Low: $2,000 or less, Medium: $2,000 – $4,500, High: $4,500 – $10,000, Very High: $10,000 or more (www.energysavers.gov).

**ENERGY STAR Version 3.0 criteria, which became effective 4/1/2011, are climate specific and are based on the U.S. climate zones (CZ) identified in 

the International Energy Conservation Code (IECC) 2009 as defined by the U.S. DOE Building Energy Codes Program (www.energycodes.gov).

***An 8.2 HSPF air-source heat pump will qualify for ENERGY STAR in Climate Zones 4 – 8 if it is combined with an ENERGY STAR-qualified dual-

 fuel backup furnace.

CEE = the Consortium for Energy Efficiency, www.cee1.org

Annual Fuel Utilization Efficiency (AFUE): AFUE is the amount of fuel converted to space heat in proportion to the amount of fuel entering the boiler or 

furnace; expressed as a percentage. It does not include the electricity consumption of the fan and controls.

Coefficient of Performance (COP): COP is a measure of efficiency for heat pumps in the heating mode that represents the ratio of total heating capacity 

to electrical energy input. For example, if a heat pump has a COP of 3, it will deliver three units of energy for every one unit of electricity consumed. 

Heating Seasonal Performance Factor (HSPF): HSPF is a measure of a heat pump’s energy efficiency over one heating season. It represents the total 

heating output of a heat pump (including supplementary electric heat) during the normal heating season (in Btus) as compared to the total electricity 

consumed (in watt-hours) during the same period. 

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ENERGY RENOVATIONS HVAC
Combustion

Air

Draft Hood/ 

Diverter

2.1 Furnaces 

More than 65% of U.S. homes are heated with central forced-air 

furnaces. Most furnaces heat air by burning gas, oil, or propane. 

Some use electricity to heat an element. The furnace burner is 

located in the air handler box along with a fan. The fan blows the 

heated air into supply ducts, for distribution to registers located 

throughout the house. Air from individual rooms or common areas 

is drawn into return registers and brought back through return ducts 

to the furnace air handler where it is reheated and redistributed. 

2.1.1 Furnace Efficiency

The efficiency of a furnace or boiler is measured by annual fuel 

utilization efficiency (AFUE). AFUE is the ratio of heat output 

of the furnace or boiler to the total amount of fuel consumed by a 

furnace or boiler. An AFUE of 90% means that 90% of the energy 

in the fuel becomes heat for the home and the other 10% escapes out 

the vent pipe and through the furnace jacket. AFUE doesn’t include 

the power consumption of the fan and controls. Nor does it include 

heat losses of the duct system, which can be up to 30% or more 

when ducts are leaky, poorly insulated, and located in an uninsulated 

attic or crawlspace. If not properly maintained, the actual efficiency 

of the furnace can be significantly lower than the rated efficiency.

2.1.1.1 Low-Efficiency Furnaces (Less than 78%)

While nearly all furnaces sold today have an AFUE of at least 80%, 

many older, less efficient furnaces in the 56% to 72% range are still in 

operation, including even old coal burners that have been switched 

over to oil or gas. If a furnace has a pilot light, it was probably 

installed prior to 1992 and likely has an efficiency of less than 72%. 

Old gas furnaces may lack a vent damper (which saves energy by 

limiting the flow of heated air up the chimney when the heating 

system is off). 

Older style furnaces can be called draft-hood furnaces because they 

draw combustion and dilution air from the room in which they are 

located; the dilution air enters through a draft hood (also called 

a draft diverter). Oil furnaces use a barometric damper instead 

of a draft diverter for dilution air in the chimney or vent system 

to decouple the burner from the chimney, thus avoiding poor 

combustion. 

Older style furnaces also rely on natural draft to carry exhaust 

gases out of the home. The combustion gases exit the home 

Furnace and Boiler 

Equipment Efficiency

AFUE (annual fuel utilization efficiency) 

is the amount of fuel converted to space 

heat in proportion to the amount of 

fuel entering the boiler or furnace; it is 

expressed as a percentage. It does not 

include the electricity consumption of 

the fan and controls. 

In 1987 the federal minimum efficiency 

standard was set at 78% AFUE for gas 

and oil furnaces, 75% for steam boilers, 

and 80% for hot water boilers, effective 

1992, per the National Appliance Energy 

Conservation Act of 1987 (NAECA). In 

2007 new efficiency minimums were 

set at 80% AFUE for gas furnaces, 

82% for oil furnaces, 82% for gas-fired 

hot-water boilers, and 83% for oil-fired 

hot-water boilers, effective 2015 (LBNL 

2011). The furnace efficiency standard is 

scheduled to be revised in 2011, with new 

requirements becoming effective in 2016.

Older low-efficiency (<72%) gas furnaces 

relied on natural draft to bring in combustion 

air and exhaust pollutants. The burn was 

less efficient and a lot of heat was lost up 

the chimney.

8 August 2011

ENERGY RENOVATIONS HVAC
Burner

Combustion Air

through the chimney using only their buoyancy, combined with the 

stack effect of the chimney’s height. Naturally drafting chimneys 

can have problems exhausting the combustion gases because of 

chimney blockage, wind, or depressurization of the home, which 

can overcome the buoyancy of the gases. Depressurization is a 

situation that can occur if more air is being pulled out of the 

home than is being drawn into the home through air leaks or 

intentional ventilation. Certain changes in the home can lead to 

depressurization, for example, if a new kitchen range is installed 

with a high-powered exhaust fan or if a significant amount of air 

sealing is done. These changes could possibly increase the risk of 

backdrafting, where exhaust products spill back into the house 

rather than going up the flue. A certified energy contractor will 

conduct combustion safety testing as part of any combustion 

appliance repair or replacement or air sealing project. The testing 

will ensure that the furnace and combustion appliances have 

adequate combustion air and are venting properly. 

2.1.1.2 Mid-Efficiency Furnaces (80% to 82%)

Mid-efficiency (80% to 82%) furnaces have no draft hood. Instead, 

they use fan-assisted draft with a fan located at the outlet (draft 

inducer) of the heat exchanger to create a regulated flow of 

combustion air. This design change increased efficiency from 65% 

AFUE in atmospheric draft furnaces to over 80% in fan-assisted 

furnaces. Fan-assisted draft minimizes the risk of backdrafting.

For furnaces with an oil burner, one way to determine the age and 

efficiency is to look at the nameplate. If the oil furnace has a nameplate 

motor speed of 1,725 rpm, it is most likely an older model with a less 

efficient burner. Models with a nameplate motor speed of 3,450 are 

newer than 20 years old and have a flame retention burner that wastes 

less heat; they have a steady-state efficiency of 80% or more.

2.1.1.3 High-Efficiency Furnaces (90% to 98%)

The most efficient furnaces available today are sealed-combustion 

(direct-vent) condensing furnaces, which have efficiencies of 90% 

to 98%. About 12% of the heat from the combustion process is 

captured in water vapor as latent heat. A condensing furnace 

condenses this water vapor through a secondary heat exchanger 

to capture the heat rather than letting it escape up the flue. This 

technological advance enabled gas furnaces to jump from 82% 

AFUE to 90% AFUE or higher (ACEEE 2011). There are no gas 

furnaces with AFUE ratings between 83% and 89% because of 

problems arising from condensation in the heat exchangers that 

occur within this range. 

Mid-efficiency furnaces (80% to 82%) use 

fan-assisted combustion systems to pull 

flue gases through the heat exchanger. No 

dilution air is required for the vent system, 

which is still buoyancy-driven.

High-efficiency (90% to 98%) furnaces add 

a second heat exchanger to pull more heat 

out of exhaust vapor, then vent emissions 

directly outside, eliminating the risk of 

back-drafting flue gases into the home.

August 2011 9

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ENERGY RENOVATIONS HVAC
High-efficiency condensing furnaces avoid back-drafting issues 

by having sealed combustion. These furnaces are designed to vent 

exhaust gases (combustion products) directly to the outside through 

a dedicated vent pipe. They should also be installed with a second 

vent pipe to bring outside air directly into the combustion chamber. 

Although a condensing unit costs more than a non-condensing 

unit, the condensing unit will save money in fuel costs over its 15- to 

20-year life and is a particularly wise investment in cold climates.

Both mid- and high–efficiency furnaces are available with two-stage 

gas valves, two-speed draft fans, and variable-speed blower fans, 

which reduce their electricity usage by better matching air flow rate 

to the heating needs of the home.

Nearly all combustion furnaces sold today meet or exceed 80% 

AFUE. About one-third of current sales on a national basis are 90% 

AFUE or better. In just the past 10 years alone, about 7.5 million 

condensing furnaces went into replacement installations in the 

United States (ACEEE 2011). 

The AFUE rating for an all-electric resistance furnace or boiler is 

between 95% and 100%; because there is no combustion, no heat 

loss occurs up the flue, but there may be some heat loss through the 

furnace housing. However in some parts of the country, electricity 

is expensive to purchase and it can be expensive to produce from an 

environmental standpoint as well, making electric heat a less costeffective option.

2.1.2 Repair or Replace?

Although older combustion furnaces have efficiencies in the range 

of 56% to 70%, modern conventional heating systems can achieve 

efficiencies as high as 98%, converting nearly all the fuel to useful 

heat for your home. Energy-efficiency upgrades like sealing ducts and 

air leaks and adding insulation, together with a new high-efficiency 

heating system, can often cut your fuel bills and your furnace’s 

pollution output in half. Upgrading your furnace or boiler from 60% 

to 90% efficiency in an average cold-climate house will save 1.5 tons 

of carbon dioxide emissions each year if you heat with gas, or 2.5 

tons of emissions if you heat with oil (ENERGY STAR calculator, 

www.energystar.gov).

A contractor can help you determine whether your furnace or boiler 

is too old, worn out, inefficient, or oversized. If it is, the simplest 

solution is to replace it with a modern high-efficiency model. A newer 

furnace may be more efficient but is still likely to be oversized.

Bigger isn’t Always Better

Many older furnaces and central air 

conditioning systems are oversized. An 

energy performance contractor can run 

energy analysis software to help you 

determine your heating and cooling 

needs after air sealing and insulation 

improvements are made. 

In the past, many HVAC contractors 

used “rules of thumb” to determine 

HVAC sizing and, as a result, many 

installed oversized systems. Today's 

trained HVAC contractor should 

determine your heating and cooling 

loads, and the right size for your HVAC 

equipment, based on calculations 

developed by the Air Conditioning 

Contractors of America (ACCA 2005; 

1995; 2009).

The ACCA published its guidelines 

in Manuals J, S, and D. Manual J 

outlines the procedures necessary to 

estimate the heat loss and heat gain of 

residential structures. Manual S provides 

guidance for equipment selection 

based on load calculations. Manual 

D describes proper duct sizing and 

design. 

It should be noted that, in a cold 

climate, if the homeowner chooses to 

install an air-source central heat pump 

for heating and cooling, the contractor 

may opt for a larger size heat pump 

than indicated by Manual S to minimize 

the need for back up heat. This is a 

tradeoff—as the heat pump may then 

be oversized for the cooling load. Also, 

with the variable-speed motors and 

variable refrigerant flow compressors 

now available in some of the newest 

models of furnaces and heat pumps, 

oversizing is less of an issue because 

the equipment can modulate to operate 

at lower, more energy-efficient speeds 

when the demand is lower.

10 August 2011

ENERGY RENOVATIONS HVAC
If you plan to make energy-efficiency improvements to your home at 

the same time that you replace your furnace, talk to your contractor 

about how they will affect your furnace system. With a better 

building envelope, the new furnace or boiler can sometimes be a 

smaller size than the original, which can save you money. Whenever 

you make energy efficiency upgrades, your contractor should test to 

make sure that any new and existing combustion appliances (such as 

a furnace, water heater, or clothes dryer) still operate safely. 

When shopping for high-efficiency furnaces and boilers, look for 

the ENERGY STAR® label. The Consortium for Energy Efficiency 

also provides efficiency ratings and HVAC information at www.cee1.

org. Invest in the highest efficiency system you can afford, especially 

if you live in a cold climate. You can estimate the annual savings 

from heating system replacements by using Table 2.2, which shows 

how much you'll save for every $100 you spend in fuel when you 

replace your old furnace with a more efficient furnace. For example, 

if you currently spend $1,000 per year on cooling costs and you 

switch from an AFUE 65% furnace to an AFUE 95% furnace, you 

could save about $320 per year in heating costs. The table assumes 

that both furnaces have the same heat output. However, most older 

systems are oversized, and will be particularly oversized if you 

significantly improve the energy efficiency of your home. Because of 

this additional benefit, your actual savings in upgrading to a new, 

smaller system or one with a variable speed motor could be higher 

than indicated in the table.

Table 2.2. How much you'll save when you increase your 

heating equipment efficiency:* 

Annual Estimated Savings for Every $100 You Spend on Fuel

(Source: www.energysavers.gov)

Existing System AFUE New/Upgraded System AFUE

75% 80% 85% 90% 95%

50% $33 $38 $41 $44 $47

55% $27 $31 $35 $39 $42

60% $20 $25 $29 $33 $38

65% $13 $19 $24 $28 $32

70% $7 $13 $18 $22 $26

75% ---- $7 $12 $17 $21

80% ---- ---- $6 $11 $16

85% ---- ---- ---- $6 $11

90% ---- ---- ---- ---- $5

*Assuming the same heat output

A Furnace Tune-Up 

Have an HVAC technician tune-up your 

furnace to improve its efficiency and 

check for problems that may justify a 

replacement. (See www.energysavers.gov 

“Furnaces and Boilers” for more details.) 

• Test for flue gas spillage and fix.

• Check the condition of the vent 

connector and chimney. 

• Check heat exchanger for cracks or leaks. 

• Adjust temperature controls for efficiency 

and comfort. 

• Adjust blower control and supply-air 

temperature. 

• Clean and oil the blower motor. If this is 

an old, <75% efficient furnace; most midand high-efficiency blower motors are 

permanently lubricated. 

• Remove dirt, soot, and corrosion from 

the furnace or boiler. 

• Check fuel input and flame 

characteristics, and adjust if necessary. 

• Air seal connections between the furnace 

and main ducts. 

ANSI/ACCA HVAC Standards

The Air Conditioning Contractors 

of America has produced several 

American National Standards Institute 

(ANSI) approved standards on HVAC 

equipment installation and maintenance 

including

• ANSI/ACCA Standard #4 Maintenance of 

Residential HVAC Systems (ACCA 2010a)

• ANSI/ACCA Standard #5 HVAC Quality 

Installation Specification (ACCA 2010b)

• ANSI/ACCA Standard #6 Restoring the 

Cleanliness of HVAC Systems (ACCA 

2010c)

• ANSI/ACCA Standard #9 Quality 

Installation Verification (ACCA 2010d).

August 2011 11

11

ENERGY RENOVATIONS HVAC
If your furnace is less than 15 to 20 years old and you decide to keep 

it, talk to your contractor about options for improving its efficiency. 

Repairing the furnace and its distribution system to increase 

efficiency may be an option. The costs of repairs should be weighed 

against the cost of a new furnace, taking into consideration the age 

and condition of the system. If the cost of repairs is more than half 

the cost of replacement, it is better to replace with a new system 

than to invest in repairing an old one (Krigger and Dorsi 2009). 

See the Furnace Tune-Up checklist (in sidebar) for maintenance 

activities that an HVAC technician can perform to improve your 

existing system’s efficiency.

One way to improve furnace efficiency may be to replace a singlespeed blower fan motor with an electrically commutated (ECM) 

variable-speed fan motor. Your HVAC contractor should take 

into account the size and condition of your current ducts when 

considering this option to determine if any energy savings can be 

gained. (If the ducts are poorly installed or in bad condition, an 

ECM motor will work harder to push air through, negating any 

energy savings compared to a standard split-capacitor fan motor.)

Other ways to improve HVAC energy efficiency include installing 

programmable thermostats, and pressure testing, air sealing, and 

insulating ducts. For more suggestions on improving furnace 

efficiency, see www.energysavers.gov, “Furnaces and Boilers.” See 

Section 2.1.3 of this guide for more information on ways to save 

energy with duct design, installation, and air sealing.

2.1.3 Ducts 

Heated air from the furnace is distributed throughout your home 

via ducts located in the attic, basement, crawlspace, in ceiling soffits, 

or between floors. Supply ducts supply conditioned air from the 

furnace to the rooms of your house. Return air is air that comes 

from the rooms back to the furnace for filtering and reconditioning, 

either through individual ducted returns in each room or through a 

return register located in a central place like a hallway ceiling. The 

age and condition of these ducts is a factor in deciding whether to 

keep or replace a heating system. For example, the cost of replacing 

a poorly installed, leaky duct system may justify the switch to 

ductless heat pumps.

As part of a home performance assessment, the energy contractor 

will inspect your ducts for proper installation and insulation and test 

them for duct air tightness and air flow at each register. Heating and 

cooling comfort complaints can often be addressed by fixing blocked 

registers, stuck dampers, or disconnected or damaged ducts, or by 

replacing register grilles that don't direct the air adequately.

Your contractor will test the leakiness of 

the ducts with a duct blaster test 

(Source: NREL).

Mastic is a thick sealant that is painted 

on to rigid ducts to seal seams and joints 

(Source: FSEC).

If you are adding ducts, you will save 

energy by placing them inside the living 

space in compact duct runs, such as in a 

dropped hallway chase (Source: BSC).

12 August 2011

ENERGY RENOVATIONS HVAC
A Word about Chimneys

If you are upgrading to a 90% or 

higher condensing furnace or boiler, 

it will have its own dedicated exhaust 

and may no longer use the chimney. 

If no other appliances exhaust 

through the chimney, it can be closed 

up or removed, reducing chimney 

maintenance costs and possibly adding 

living space to the home. If another 

appliance, such as an atmospheric 

vented gas water heater, still uses 

the chimney, the chimney may now 

be oversized, which could lead to a 

situation where the chimney provides 

inadequate draft allowing combustion 

exhaust gases to spill back into the 

home. The chimney will need to be 

relined and sized to the water heater 

alone, or it may be less expensive, 

and more safe, to replace the old 

water heater with a higher efficiency 

sealed combustion water heater. If 

you are replacing an old furnace with 

a mid-efficiency 80% to 82% furnace 

or boiler (90%+ is recommended), the 

chimney may need to be relined and 

sized to handle the lower volume, lower 

temperature exhaust gases. The cost 

of relining the chimney may justify 

upgrading to a 90%+ furnace.

2.1.3.1 Existing Ducts

If you decide to replace your HVAC equipment but keep the existing 

ducts, your energy contractor can assess the ducts for proper sizing, 

balanced pressures, and adequate air flow to each register, and 

adequate return air to the furnace. 

Your contractor will test the leakiness of the ducts with a Duct 

Blaster test. For some comparison of what is considered leaky, the 

International Energy Conservation Code (IECC) 2009 requires that 

duct leakage be tested in new construction if the ducts are located 

in unconditioned space, like an attic or crawlspace. According to the 

IECC 2009, total duct leakage in a finished house should not exceed 

12 cubic feet per minute (cfm) per 100 ft2 of conditioned floor area 

at 25 Pascals of pressure if the ducts are located in unconditioned 

space. (Duct leakage must be less than or equal to 6 cfm/100 ft2 CFA 

at 25 Pa if the ducts are tested at rough in, per IECC 2009 403.2.2.) 

For the IECC 2012, these requirements will go to 4 cfm total 

leakage/100 ft2 CFA at 25 Pa, whether tested at rough in or finished 

construction. 

If the duct system is shown to be leaky, steps can be taken to seal 

the ducts, joints, and air handler cabinet. Ducts and air handler 

connections should be sealed with mastic, which is painted on all 

seams and joints. Flex duct connections should be reinforced with 

approved metal tape and compression bands (clamps). Cloth-backed 

duct tape should not be used; DOE studies have shown that it can 

dry out and fail within months (Sherman et al. 2000). As noted 

in Chapter 1, testing out should be done by a certified energy 

contractor after duct sealing to make sure no combustion safety 

problems are introduced (Cummings et al. 2011).

If your ducts are located in conditioned space (inside the living area 

of the house, for example in a dropped soffit or between floors), an 

attempt should still be made to seal the ducts wherever accessible, at 

least at the registers, boots, and connection to the air handler.

Ducts not located in conditioned space should be insulated to R-8 

for supply ducts and R-6 for return ducts (IECC 2009 403.2). Ducts 

within the house should be insulated if possible to ensure heated and 

cooled air gets where it is needed—and to reduce the possibility of 

condensation and mold on or inside the ducts. 

One common problem with existing duct systems is lack of adequate 

return air flow, which can hamper furnace performance. Return air 

is air that comes from the rooms back to the furnace either through 

individual ducted returns in each room or through a central return 

If duct pressure testing shows that 

your existing duct system has pressure 

imbalances or inadequate return air, there 

are several possible fixes to allow air to 

flow back to the central return air grille, 

including installing jump ducts or transfer 

grilles between closed rooms and common 

spaces (Source: BSC).

Bedroom Hallway

Jump Duct

August 2011 13

13

ENERGY RENOVATIONS HVAC
register located in an open area like a hallway. Central return ducts 

are often undersized in existing duct systems; installing a large 

central return duct can improve system performance and reduce 

noise. There are several options that allow air to return from rooms 

that are often closed. Individual return air ducts can be installed in 

these rooms; transfer grilles can be installed in the doors or walls; 

jump ducts can be installed in the ceilings to connect the rooms to 

open areas. Some contractors use door undercuts, but these may not 

provide adequate air flow.

2.1.3.2 New Ducts

If your contractor recommends installing a new duct system in the 

house, there are several things that can be done to ensure the new 

duct system is as efficient as possible. It should be sized according to 

the ACCA Manual D or equivalent.

Work with your HVAC contractor to see if it is possible to install the 

ducts and furnace in conditioned space inside your home. Building 

America has shown this can be a source of significant energy savings 

and can also improve indoor air quality because leaking ducts aren’t 

heating, cooling, or drawing air from unintended places and furnace 

and air-conditioning equipment isn't having to overcome the effects 

of cold crawlspaces or hot attics. Putting the ducts inside can be 

accomplished in several ways. The ducts can be installed in a dropped 

ceiling chase in the main hallway of a one-story house or between 

floors in a two-story house that uses open-web floor trusses (Beal et 

al. 2011). Another option is ducts can be installed in an insulated 

basement or an insulated attic (i.e., where the insulation is installed 

along the underside of the roof deck instead of on the ceiling 

deck.) The ducts could also be installed in an insulated, air-sealed 

crawlspace (i.e., where insulation is on the walls of the crawlspace, 

not the underside of the floor). The air handler can be located in a 

utility closet inside the house or in an air-sealed closet in the garage. 

Duct design and installation is also important. In homes that are 

well insulated, the ducts can be laid out in a compact duct design 

with shorter runs and registers mounted on inside walls for adequate 

heating with less distribution losses. Your HVAC contractor should 

select supply registers for adequate throw, drop, and spread of 

conditioned air. 

For adequate air flow, ducts should be laid straight with adequate 

support and no sharp turns. If flex duct is used, it should be fully 

stretched and supported at least every 4 feet with strapping at least 

1.5 inches wide to prevent sagging. Care should be taken to avoid 

tearing, compressing, or kinking the flex duct during installations 

(CEC 2009). 

This Building America builder puts ducts 

inside the home instead of above the 

insulation where they would be exposed to 

cold and hot attic conditions.

14 August 2011

ENERGY RENOVATIONS HVAC
2.2 Electric Heaters

Currently, 14% of U.S. single-family homes use electric resistance 

heat to heat their homes: almost 11% have an electric central forcedair furnace, and more than 3% use some form of electric space 

heating. An additional 10% use heat pumps, which will be described 

in the next section. 

2.2.1 Electric Central Furnaces

Electric forced-air furnaces distribute heat with an air handler and 

ducts, just like gas furnaces (see Section 2.1 for more on furnaces and 

ducts). The AFUE rating for an all-electric furnace is 95% to 100%. 

This is because electric furnaces provide heat through resistance, 

not combustion, so there are no heat losses up the chimney. All of 

the electricity is converted to heat, minus a small amount of heat 

loss through the air handler cabinet. This AFUE rating does not 

include any heat losses through leaky or uninsulated ducts. However, 

although it varies based on local utility rates, electricity is still one of 

the most expensive heating fuels. 

If you have an electric furnace and your duct system is good, 

consider switching to a high-performance air-source heat pump. 

Electricity savings can be 30% or more when compared with electric 

resistance heating.

2.2.2 Room Heaters 

Room heating here refers to heating systems that heat one room 

or area of a home, unlike central systems, which distribute heat 

throughout the entire house via ducts or piping. Electricity is the 

most common fuel type for room heaters, but there are other fuel 

types as well. 

Unvented combustion space heaters, which can release dangerous 

combustion gases into the home, are illegal in some states and 

should not be used. The use of portable space heaters is also not 

recommended because of their inefficiency and potential burn and 

tripping hazards. 

In an average- or large-sized home with minimal or average 

insulation, electric resistance room heaters (baseboard or wallmounted) are not typically a cost-effective method for heating 

the whole house over the long term. In a very well-insulated and 

air sealed home that requires little heating, they can be a costeffective choice. They can also be a cost-effective choice for heating 

infrequently used rooms when the main living areas are heated with 

ductless heat pumps or radiant floor heat. 

Building America's Consortium for 

Advanced Residential Buildings (CARB) 

worked with Rural Development, Inc. 

to design a community of townhouses 

in western Massachusetts that were so 

well insulated that a two-stage sealedcombustion gas space heater met the 

design load. The heaters had a capacity 

of 10,200 Btu/hr on low fire and 16,000 

Btu/hr on high fire with an AFUE of 83% 

(Source: Rural Development, Inc.).

Although not cost-effective as your main 

heating source, in a home with average 

insulation, baseboard electric heaters 

are an inexpensive way to provide 

supplemental room heating. 

August 2011 15

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ENERGY RENOVATIONS HVAC
2.2.3 Zoning

Many homeowners who have forced-air systems will shut vents and 

close a door in a room they aren’t using, thinking that this saves 

energy. This is not recommended because it can reduce airflow 

through the air handler, causing pressure imbalances, putting stress 

on the duct connections, and affecting air quality if you are using 

your air handler for ventilation. Zoning can be accomplished with 

central forced-air systems, using damper controls installed in the 

ducts by an HVAC professional, but the dampers will affect system 

efficiency and balance. In large homes, zoning of central heating 

and forced-air systems is more commonly (and more effectively) 

accomplished by installing multiple systems, with one unit per floor. 

Hydronic heating systems can be configured, with piping and valves, 

to provide zone heating. Zone control works best in homes where 

the different zones can be isolated from each other with closable 

doors. Never shut off the heat entirely in an unused part of your 

home because condensation could form on cold inside wall surfaces 

leading to mold. Keep all rooms at a minimum of 50°F in the winter 

to prevent water pipes from freezing.

Room heaters can be used as an inexpensive way to provide zone 

heating when a central forced-air system is the main heating system 

for the home. Other forms of room heating that might be considered 

for supplemental heating or for additions include ductless heat 

pumps (described in Section 2.3.2), electric radiant wall and ceiling 

panels, active solar space heating (described in Section 2.6), sealedcombustion gas room heaters, and high-efficiency wood or pellet 

stoves (see Section 2.5).

Ductless heat pumps can provide efficient 

zoned heating and cooling.

16 August 2011

ENERGY RENOVATIONS HVAC
Outdoor Coils

Evaporator

Compressor

Expansion 

Valve

Indoor Coils 

Condenser

Gas condenses 

into a liquid, 

releasing 

heat inside

Liquid 

evaporates 

into gas,

pulling heat 

from outside

Air-Source Heat Pump Heating Cycle – In heating mode, an air-source heat pump 

evaporates a refrigerant in the outdoor coil. As the liquid evaporates, it pulls 

heat from the outside air. The hot gas is compressed and pressurized as it passes 

through the compressor to the indoor coil (or condenser). Here it condenses to 

a high-pressure liquid, releasing heat to the inside of the house as it cools. The 

liquid then passes outside and through a pressure-lowering expansion valve and 

enters another heat exchanger, the evaporator, where the fluid absorbs heat and 

boils. The pressure changes caused by the compressor and the expansion valve 

allow the gas to evaporate at a low temperature outside and condense at a higher 

temperature indoors. In cooling mode, the reverse happens.

Air-Source Heat Pump 

in Heating Cycle

Heat Pump Heating Efficiency

Heating Season Performance Factor 

(HSPF) is a measure of a heat pump’s 

energy efficiency over one heating 

season. It represents the total heating 

output of a heat pump (including 

supplementary electric heat) during 

the normal heating season (in Btus) 

as compared to the total electricity 

consumed (in watt-hours) during the 

same period. Heat pumps and furnaces 

must have an HSPF of 7.7 or higher (per 

federal requirements that went into 

effect in 2006).

Ground-source heat pump efficiency 

is also measured by Coefficient of 

Performance (COP). The COP is a 

measure of efficiency in the heating 

mode that represents the ratio of total 

heating capacity to electrical energy 

input. For example, if a heating system 

has a COP of 3, it will deliver three units 

of energy for every one unit of electricity 

consumed. Heating COPs for heat 

pumps range from 1.5 to 4 depending on 

climate, design, and installation.

2.3 Heat Pumps

A heat pump uses the same refrigeration cycle technology as 

your home’s refrigerator or air conditioner pooling heat from one 

environment and dumping it in another. Because a heat pump is 

equipped with a reversing valve, it can both heat and cool your 

home. During the heating season, heat pumps move heat from the 

outdoor air to warm your house; during the cooling season, the cycle 

is reversed. 

About 85% of the installed residential heat pumps are air-source 

heat pumps, which transfer heat between the house and the outside 

air. These can be either large central units that distribute heat and 

cooling through ducts (see Section 2.3.1) or smaller ductless units 

that are installed in one or more areas of the home for zoned heating 

and cooling (see Section 2.3.2). Ground-source and water-source 

heat pumps are other options (described in Section 2.3.3). More 

information on these and other types of heat pumps, including 

absorption or gas-fired heat pumps and reverse-cycle chiller heat 

pumps, can be found at www.energysavers.gov. 

August 2011 17

17

ENERGY RENOVATIONS HVAC
2.3.1 Central Air-Source Heat Pumps

Most heat pumps installed in U.S. homes are central air-source heat 

pumps that distribute heated and cooled air through ducts, just like 

a central forced-air furnace. Most of these air-source heat pumps are 

split systems meaning that the air handler (which houses the blower 

fan) is indoors and the compressor is outdoors. The air handler 

contains the blower and the inside coil for the heat pump.

Current federal law requires that air-source heat pumps have a 

minimum heating efficiency, or Heating Season Performance Factor 

(HSPF), of 7.7 and a minimum cooling efficiency of Seasonal 

Energy Efficiency Ratio (SEER) of 13. Higher efficiency central 

air-source heat pump models are available with up to 9.6 HSPF and 

SEER 23.

Because the heating efficiency of standard, central air-source heat 

pumps drops when outside temperatures drop below about 35°F, 

a backup heat source is often needed, especially in cold climates. 

Air-source heat pumps can be all-electric or dual-fuel systems. 

All-electric air-source heat pumps come equipped with electricresistance strip heaters for supplementary heat if needed. Dual-fuel 

systems combine the air-source heat pump with another source of 

supplementary heat, such as a gas furnace. Another type of central 

air-source heat pump developed in Canada for cold climates is the 

bivalent heat pump; it uses a gas- or propane-fired burner to increase 

the temperature of the air entering the outdoor coil, allowing the 

unit to operate at lower outdoor temperatures with less frost buildup 

on the outside coil (NRCan 2009). 

If you heat with electricity, a heat pump can trim the amount of 

electricity used for heating by as much as 30% to 40% compared 

to electric resistance heat. The efficiency of today's air-source heat 

pumps is one to two times greater than those available 30 years ago 

due to technical advances such as thermostatic expansion valves, 

variable-speed blowers, improved coil design, two-speed compressors 

(instead of single-speed compressors), and improved motor designs 

(www.energysavers.gov). Variable-speed compressor designs that 

better match refrigerant flow to load are in development and will 

make heat pumps more effective at lower outside temperatures. 

Variable-refrigerant-flow, ductless “mini-split” heat pumps are 

already available that can heat at 100% capacity at outdoor 

temperatures as low as 5°F. 

If you plan to install a heat pump, ask your HVAC installer to 

confirm that the existing ducts are appropriately sized for the heat 

pump. Ducts may need to be larger for a heat pump than for a gas 

A Central Air-Source Heat 

Pump Checklist 

Here is a checklist of maintenance 

activities that you or your HVAC 

contractor can do to maintain your heat 

pump’s efficiency and performance. 

(See www.energysavers.gov “Air-Source 

Heat Pumps” for more details.)

• Inspect and clean filters monthly or per 

manufacturers’ instructions.

• Vacuum or brush coils. 

• Clean the fan; oil the fan motor only if the 

manufacturer instructions specify this, 

newer models are sealed. 

• Check the fan for incorrect pulley settings, 

loose fan belts, or incorrect motor speeds.

• Inspect ductwork; make sure air flow 

is not restricted by loose insulation, 

abnormal buildup of dust, or any other 

obstacles that occasionally find their way 

through the grills.

• Be sure that vents and registers are not 

blocked by furniture, carpets, or other 

items that can stop airflow.

• Confirm that the drain pan is draining 

correctly.

Old air-source heat pumps should be 

serviced as recommended below. New 

heat pumps may be significantly more 

efficient and can operate at wider 

temperature ranges.

18 August 2011

ENERGY RENOVATIONS HVAC
or oil furnace because furnaces generally deliver air to the living 

space at between 130°F and 140°F. Heat pumps provide air at about 

80°F to 115°F so more air needs to be delivered to provide the same 

amount of warmth (NRCan 2009). Your HVAC contractor should 

confirm that the supply air registers achieve a “throw” appropriate 

for a heat pump. Choosing the right register design can be important 

for minimizing comfort complaints because heat pumps blow more 

air at cooler temperatures than gas- or oil-fired furnaces. 

Some researchers suggest central-air-source heat pumps may need to 

be slightly oversized, to enable the system to provide enough warmth 

without turning on the backup heat.

2.3.2 Ductless Heat Pumps

High-performance ductless heat pumps are an efficient alternative 

to central ducted heat pump systems. Ductless heat pumps are 

sometimes referred to as mini-split heat pumps because they consist 

of a single outside compressor/condenser unit connected to one 

or more wall- or ceiling-mounted indoor air handler units. They 

can provide zone heating and cooling without ducts. The outdoor 

units are mounted on the wall or on a concrete or stone pad outside 

the house; refrigerant tubing connects the inside and outside units 

through a small hole in the wall.

Ductless heat pumps have been used in Asia and Europe since the 

1970s and they comprise 80% to 90% of the residential HVAC 

market there. They have been used in U.S. commercial buildings 

since the 1980s, but they still comprise less than 3% of the U.S. 

residential market (Karr 2011). They are 25% to 50% more efficient 

than electric baseboard or wall heaters (NEEA 2009). Ductless 

heat pumps provide increased energy savings over standard heat 

pumps in several ways. Because they are ductless and mounted 

inside conditioned space, they avoid the distribution losses of a 

central furnace that has leaky ducts installed in an unheated attic 

or crawlspace. Ductless heat pumps provide zoned heating because 

units can be turned off or not installed in rooms that aren’t being 

used. They use a much smaller blower than central units; however, 

more than one inside unit is typically needed to serve the whole 

house. Up to eight inside units can be connected to one outside unit. 

Advances in technology in recent years have increased performance 

to the point that units are now available with heating efficiencies as 

high as 12 HSPF and cooling efficiencies as high as SEER 26. The 

most efficient ductless heat pumps use a variable-speed compressor 

that can vary the refrigerant flow. They also have linear expansion 

Ductless Demo Hits 10,000

The Northwest Ductless Heat Pump 

Project is a large-scale ductless heat 

pump demonstration project conducted 

by the Bonneville Power Administration 

and the Northwest Energy Efficiency 

Alliance that has installed more than 

10,000 ductless heat pumps since 

2009. See their site (www.nwductless.

com) for more information on ductless 

heat pumps, including installation 

tips, product recommendations, and 

performance details.

Ductless heat pumps are sometimes 

referred to as mini-splits because they 

have a single outdoor unit and one or more 

small, wall-mounted indoor air handler 

units. The outdoor unit can be located on 

a concrete pad or mounted on an exterior 

wall (Source: Northwest Energy Works).

August 2011 19

19

ENERGY RENOVATIONS HVAC
Ground,

Looped

Collector

Ground,

Horizontal 

Collector

Ground,

Vertical

Collector

Pond, 

Looped

Collector

Ground

Source

Heat Pump

valves rather than open/close valves, and multi-speed rather than 

single-speed fans to continuously match the heating or cooling 

load. Unlike conventional air-conditioning and heating systems 

that stop and start repetitively, the inverter technology adjusts the 

motor speed, allowing the system to adapt more smoothly to shifts 

in demand with less temperature variation and much lower energy 

use. When maximum capacity is not needed, compressor revolution 

and power decreases, increasing energy efficiency. For example, one 

model reports a capacity range of 3,100-24,000 Btus in heating mode 

and 3,800-14,500 Btus in cooling mode. 

The best performing ductless heat pump models perform at a much 

wider temperature range than standard heat pumps. Some models 

can operate at an outdoor temperature range of -5°F to 75°F for 

heating and 14°F to 115°F for cooling, eliminating the need for 

backup heat sources in most locations. 

2.3.3 Ground-Source Heat Pumps

A ground-source heat pump is an electric heat pump that 

exchanges heat with the ground or ground water, instead of air. The 

temperature of the earth below the surface remains fairly constant 

at a U.S. average of 55°F throughout the year (cooler in the north, 

warmer in the south) with less than 20 degrees variation over the 

year at 5 feet below the surface. 

Unlike air-source heat pumps, which draw 

heat from the air, ground-source heat 

pumps use the moderate temperature 

below ground to achieve high efficiencies 

of 300%+ year round. In a closedloop system, piping loops can be laid 

horizontally, vertically, or looped in the 

ground or in ponds. These collector options 

are shown in heating mode with fluid 

circulating to collect heat (red) from the 

ground, release it to the indoor heat pump 

through a heat exchanger, and return 

cooled fluid (blue) to collect more heat.

Collector Configuration 

Options for Closed-Loop 

Ground-Source Heat Pumps

20 August 2011

ENERGY RENOVATIONS HVAC
Because heat is exchanged with the ground rather than the outside 

air, which has more erratic temperatures, ground-source heat pumps 

remain a very efficient source of heating and cooling all year. 

Additional efficiency is gained by using water rather than air as the 

heat-exchange fluid (Karr 2011). (The ground-source systems we are 

describing here do not include the geothermal systems that use high 

below-ground temperatures associated with volcanic activity for heat 

and power production.) 

Ground-source heat pumps may be closed-loop or open-loop 

systems. A “closed-loop” ground-source heat pump circulates water 

(or a mixture of water and anti-freeze) from the heat pumps to 

horizontal or vertical pipes that are buried in the ground in contact 

with the earth, which serves as a heat source in winter and heat 

sink in summer. After exchanging heat with the ground, the water 

is circulated back to the heat pumps in a closed loop. Closed-loop 

configurations include piping laid in horizontal rows or loops in 

trenches 5 to 10 feet deep, or vertical loops inserted in boreholes 

that are 75 to 500 feet deep and filled in with bentonite or other 

grout materials to aid heat transfer to the soil. Closed loops can 

also be laid in a private pond to exchange heat with the pond water. 

Another much less common type of closed-loop system is the direct 

exchange heat pump, which circulates refrigerant rather than water 

or antifreeze directly through the ground in a single closed loop 

of copper tubing. This system uses more refrigerant and copper 

tubing, which are expensive but are more efficient at heat transfer so 

less tubing length and thus less digging is required.

An “open-loop” ground-source heat pump uses groundwater from a 

well as the heat source and heat sink. The water circulates through 

the heat pump(s) once and is returned to the ground through a 

separate injection well or through surface discharge (EIA 2010). 

In heating mode, the heat is transferred from the ground loop to the 

refrigerant loop in the heat pump, then distributed to the home via 

a second heat exchanger, by warming either air, which is blown over 

the heat exchanger and through ducts just like a central furnace, or 

fluid, which flows through tubing installed in the floors to provide 

radiant heat to the rooms.

Because the compressor for the ground-source heat pump is 

located inside the home, it is subject to much less wear and tear 

than the outdoor compressor fans of air-source heat pumps, and 

as a result, ground-source heat pump equipment lasts longer and 

maintains its efficiency better than air-source heat pumps. Twospeed compressors that more effectively match demand and scroll 

compressors with fewer moving parts have dramatically increased 

efficiency since the 1990s.

Warm Air 

to House

Blower

Secondary 

Heat 

Exchanger

Warm Antifreeze 

into Heat Pump

Cooler Antifreeze 

out of Heat Pump

Hot Water Heater

Desuperheater

Hot

Refrigerant

Out

Cold Air Return

Refrigerant Piping

Compressor

Reversing 

Valve

Primary 

Heat 

Exchanger

Expansion 

Device

Ground-Source Heat Pump in 

Heating Mode

In heating mode, the heat is transferred 

from the ground loop to the refrigerant 

loop in the heat pump and then distributed 

to the home via a second heat exchanger, 

by warming air, which is blown over the 

heat exchanger and through ducts just 

like a central furnace. The heat can also 

be distributed via heated fluid, which 

flows through tubing installed in the floors 

to provide radiant heat to the rooms. In 

cooling mode, a desuperheater can use 

some of the heat pulled from the home's 

interior to heat domestic hot water.

August 2011 21

21

ENERGY RENOVATIONS HVAC
Most ground-source heat pumps are equipped with a desuperheater, 

which is an auxiliary heat-recovery system that can be connected to the 

home’s water heater tank to provide up to 25% to 50% of the home’s 

domestic hot water (Smith and Arco 1996). Because they use extra heat 

from the cooling process they are more effective in hot climates where 

the heat pump is in cooling mode most of the time. 

Ground-source heat pumps can have high installation costs because 

they require drilling or trenching (CEC 2011). If there is a pond on 

the property, the loops can be laid on the pond bed, a less costly 

installation than digging trenches, as long as the tubing is covered by 

8 feet of water year-round. 

Ground-source heat pumps have risen in popularity in the United 

States from 35,600 units shipped in 2000 to 115,400 ground-source 

heat pumps shipped in 2009. The ground-source closed-loop units 

shipped in 2009 had an averaged rated heating efficiency of 4.1 

Energy Efficiency Ratio (EER) Btus/hr/W and an average rated 

cooling efficiency of 20.4 EER Btus/hr/W (EIA 2010). 

Ground-source heat pump efficiencies of 300% to 600% have been 

reported, compared to 175% to 250% for central ducted air-source 

heat pumps (www.energysavers.gov). Pump power consumption 

is not usually included in the rated efficiency of the system and 

should be taken into account when considering a ground-source heat 

pump installation (Sherwin et al. 2010). Good thermal connectivity 

between the loop and ground is essential for high efficiency and soil 

irregularities can affect performance. System life is estimated at 25 

years for the inside components and 50+ years for the ground loop 

(www.energysavers.gov). 

While ground-source heat pumps can save more energy than central 

ducted air-source-heat pump systems, studies are still being done 

to determine whether their additional costs justify their installation 

over variable refrigerant flow ductless heat pumps. One option 

that has been proposed for increasing ground-source heat pump 

efficiency is combining the ground-source heat pump with the 

variable refrigerant flow technology of ductless heat pumps. In a 

modeling study of multifamily housing (using energy savings data 

that were confirmed by field studies), ground-source heat pumps 

combined with variable refrigerant flow technology cut energy use 

by 36% compared to an air-source central heat pump system, while 

ductless heat pumps cut energy use by 32% and a regular groundsource heat pump alone cut energy use by 28% (Karr 2011).

22 August 2011

ENERGY RENOVATIONS HVAC
2.4 Boilers and 

Hydronic Heating

Hydronic heating systems use steam or hot water that is heated by a 

boiler and distributed via pipes to radiators or baseboard convectors, 

or to tubes for radiant floor heating. The hot water can also be 

used to heat air via a coil and blower. The boiler may burn oil, gas, 

propane, or wood or use electricity to heat the water. The water may 

be preheated using a solar thermal system or ground-source heat 

pump. Steam is distributed via pipes to steam radiators. Hot water 

can be distributed via baseboard radiators, wall radiators, or radiant 

floor systems; or, the hot water can be used to heat air via a coil and 

blower. Steam boilers operate at a higher temperature than hot water 

boilers and are inherently less efficient, but high-efficiency versions 

of both types of boilers (up to 95%) are currently available.

The minimum federal rating for a fossil-fueled boiler is 80%. For 

more on boiler efficiency and considerations on replacing your 

existing boiler, see Section 2.1 above. Also see “Furnaces and 

Boilers” at www.energysavers.gov. 

Hydronic heating systems can provide energy and cost savings by 

being zoned to only provide heating to areas of the house that are in 

use. Zoning can be done by installing separate circulating lines, using 

zone valves controlled by separate thermostats, or using a central 

electronic controller and emitters with controls on them. 

2.4.1 Steam and Hot Water Radiators

Steam heating is one of the oldest heating technologies. Steam moves 

itself through piping without the use of pumps. Older, high-mass 

boilers are less efficient and there is also a significant lag time from 

when the boiler turns on to when the heat arrives in the radiators. 

Hot-water systems pipe the hot water to the different rooms of 

the house where heat is distributed through baseboard convectors 

or upright wall radiators (similar in design to steam radiators) or 

through radiant floor heating loops. Building America partner Building 

Science Corporation worked with Shaw 

Construction to design a hydronic heating 

system that uses baseboard radiators that 

deliver water heated by roof-mounted 

solar water heating panels. A gas-fired 

boiler provides back-up heat for these 

townhouses in Aspen, Colorado.

August 2011 23

23

ENERGY RENOVATIONS HVAC
2.4.2 Radiant Floor Heating

Hydronic radiant floor systems pump heated water through tubing, 

which is laid in a pattern underneath the floor. The cost of installing 

a hydronic radiant floor system varies by location and also depends 

on the size of the home, the type of installation, the floor covering, 

and the cost of labor. Because radiant floor heating requires lower 

temperature water than radiator heating, the water for hydronic floor 

heating can be heated or preheated with a solar thermal heating 

system or a ground-source heat pump. 

When the heat source is a ground-source heat pump, the cycling 

can be reversed in the summer to provide cooling. Radiant floor 

cooling works best in dry climates; it is not recommended in humid 

climates because of the potential for condensation to form on the 

floor surface. 

The tubing can be installed in traditional concrete slabs, a thin layer 

of concrete, or pre-grooved wood panels. The slab under the radiant 

tubing must be insulated. Some flooring types such as thick carpet 

can diminish the heat transfer ability of radiant flooring. 

Radiant heat wall and ceiling panels that distribute hot water through 

tubing installed in wall- or ceiling-mounted panels are also available. 

2.4.3 Repair or Replace

If you have an existing hydronic system that you are not ready to 

replace, talk to your contractor about what can be done to improve 

its efficiency. Hydronic systems can have problems with corrosion 

that clogs components. Some annual maintenance is required by 

homeowners and HVAC technicians. See the sidebar on this page for 

tune-up recommendations.

House Radiator

Hot Water

Floor

Expansion 

Tank

Gas-Fired Boiler

Circulating 

Pump

Cold Water

Return

Drain Cock

Water

Supply

Main 

Shut-off

Valve

Typical elements of a 

hydronic water heating 

system include a gasor oil-fired burner, a 

circulating pump, and 

a distribution system, 

and either wall radiators, 

baseboard radiators, or 

radiant floor loops.

A Boiler Tune-Up 

Proper maintenance and inspection 

by an HVAC technician can improve 

system performance for greater 

efficiency and may identify problems 

that justify replacing the boiler. (See 

energysavers.gov, “Furnaces and 

Boilers,” for more details.)

For Both Hot Water 

and Steam Systems:

• Test for carbon monoxide spillage and 

remedy if found.

• Check the condition of the vent 

connection pipe and chimney. 

• Check the heat exchanger for cracks or 

leaks. 

• Adjust temperature controls for efficiency 

and comfort.

For Hot Water Systems:

• At the start of each heating season, bleed 

air from each radiator.

• Test pressure-relief valve. 

• Test high-limit control. 

• Confirm that pressure tank is filled with 

air, not water. 

• Clean the heat exchanger. 

For Steam Systems:

• Drain some water from the boiler to 

remove sediments. 

• Test low-water cutoff safety control and 

high-limit safety control. 

• Drain the float chamber to remove 

sediments. 

• Analyze boiler water and add chemicals 

as needed to control deposits and 

corrosion.

• Check and replace clogged air vents.

• Check that radiator is level and drains 

fully when cool.

• Check and replace sticking steam traps.

• Clean the heat exchanger.

• Install reflectors behind wall radiators. 

24 August 2011

ENERGY RENOVATIONS HVAC
2.5 Wood and Pellet Heating

About 2.9 million households use wood as their primary heating 

source, and 8.9 million homes use it as a secondary heating source 

(EIA 2005). Newer wood- and pellet-burning appliances include 

models that are cleaner burning, more efficient, and powerful 

enough to heat many average-sized, modern homes. 

Traditional open masonry fireplaces should not be considered 

heating devices. Traditional fireplaces draw in as much as 300 cubic 

feet per minute of heated room air for combustion, and then send 

it straight up the chimney. Fireplaces also produce significant air 

pollution. When burning a fire in a traditional fireplace, you should 

turn your heat down or off and open a window near the fireplace. 

Close the flue when the fireplace is not in use. Consider installing 

an inflatable flue stopper in rarely used fireplaces or during summer 

months to stop air leaks.

Pellet stoves, which burn small pellets made from compacted 

sawdust, wood chips, bark, recycled paper, or agricultural crop 

waste, are among the cleanest wood-burning options. They have 

combustion efficiencies of 78%–85%, heating capacities of 8,000 to 

90,000 Btu per hour. They can be direct-vented to the outside and do 

not need a chimney. They require electricity to run the fans, controls, 

and pellet feeders.

Masonry heaters, also known as “Russian,” “Siberian,” and 

“Finnish” fireplaces, produce more heat and less pollution than any 

other wood- or pellet-burning appliance. They commonly reach a 

combustion efficiency of 90%. Masonry heaters include a firebox, 

a large masonry mass (such as bricks), and long twisting smoke 

channels that run through the masonry mass. A small hot fire built 

once or twice a day releases heated gases into the long masonry heat 

tunnels. The masonry absorbs the heat and then slowly releases it 

into the house over a period of 12–20 hours. 

New high-efficiency wood stoves with catalytic combustors have 

advertised efficiencies of 70%–80%. 

Modern fireplaces (which have vents under the firebox for drawing 

in room air, a heat exchanger, vents at the top of the fireplace 

for routing heated air, and a dedicated supply of outside air for 

combustion) provide benefits at efficiencies near those of woodstoves.

New wood stoves reach efficiencies of 

80%. Masonry heaters and pellet stoves 

are other higher efficiency options. 

These pellets, for burning and pellet 

stoves, are made from recycled products. 

August 2011 25

25

ENERGY RENOVATIONS HVAC
Before investing in a new wood-burning appliance, check with your 

local building codes department or state environmental agency about 

wood-burning restrictions.

If you have an older wood-burning appliance, consider upgrading 

to one of the newer >75% efficient appliances certified by the U.S. 

Environmental Protection Agency (EPA). More information on 

wood-burning appliances and tax credits can be found on the EPA 

website, www.epa.gov/burnwise/appliances.html#woodstoves. 

2.6 Solar Heating

Solar energy is a hot topic in buildings today. When you mention 

solar, many people think of photovoltaic (PV) panels mounted on 

the roof to produce electricity. This electricity can certainly be used 

by homeowners to offset the cost of heating and cooling, especially 

with electric equipment like heat pumps. 

However, solar energy can also be used to directly heat homes, using 

either passive or active methods. See www.energysavers.gov/yourhome/space_heating_cooling for more information about using the 

sun to heat and cool your home.

Both photovoltaic and solar thermal water heating panels are mounted on the 

roof of this duplex in the Wisdom Way Solar Village, an affordable housing project 

in western Massachusetts built by Rural Development, Inc. with design assistance 

from the Consortium for Advanced Residential Buildings (CARB), a Building 

America research team (Photo source: Steven Winter Associates). 

26 August 2011

ENERGY RENOVATIONS HVAC
2.6.1 Passive Solar Heating

Passive solar heating uses a home's design elements to take 

advantage of sunlight that reaches into the living spaces of the 

home. Passive solar design features like thermal mass walls and 

floors, sun rooms, and south-facing building orientation are most 

easily incorporated when designing a new home. However, existing 

buildings can be adapted or “retrofitted” to passively collect and use 

solar heat. The energy savings from passive solar heating are very 

dependent on climate. It may not be cost-effective to add passive 

heating features in a cold climate location with few sunny winter 

days. In hot climates the extra cooling load may offset any winter 

heat gains. Regardless of the climate, when considering passive solar 

heating options, know that you'll have to take steps to minimize 

unwanted heat gain during the summer. This might include planting 

shade trees, adding awnings, or increasing roof overhangs. 

THERMAL MASS WALLS OR FLOORS – A thermal mass wall or 

thermal mass floors can be incorporated into a remodeling project. A 

thermal mass floor or wall is made of a material that will absorb and 

retain a large amount of heat, for example, a brick wall or concrete 

slab floor. The thermal mass is located where it will absorb sun 

through a large window for several hours of the day, then, because 

heat moves from hot to cold, the mass will release that heat gradually 

during the evening hours. In the morning, when the wall or floor has 

cooled, it will be ready to absorb more heat. 

SUN ROOM – A sun room or sun porch can be added that has large 

south, and possibly east- and west-facing windows. The sun room 

should be separated from the rest of the house by an insulated wall 

with openable doors and shaded windows so that heat can be let in 

during the winter and kept out to avoid overheating the house during 

the summer. 

SOUTH-FACING WINDOWS – If you are already planning to add 

or replace windows as part of a remodel and if you live in a cold 

or mixed climate that gets adequate sun during the winter, you may 

want to consider adding larger, south-facing windows that can let in 

winter sun but are protected by overhangs, awnings, plants, or shades 

to keep out summer sun. The windows should be high-performance 

ENERGY STAR-rated windows to minimize heat loss.

If you live in a cold climate and are 

replacing windows as part of a remodel, 

consider that windows placed on the south 

side can provide beneficial solar heat gain 

in the winter, provided they are shaded 

from excessive heat gain in the summer. To 

be effective they should have a solar heat 

gain coefficient of >0.6 to maximize winter 

heat gain, a U-factor of <0.3 to reduce 

conductive heat transfer, and a high visible 

transmittance (www.energysavers.gov 

"Passive Solar Window Design").

Building America has produced a solar 

guide that can help homeowners and 

contractors understand their options in 

solar water heating and photovoltaics. The 

guide “Building America Best Practices 

Series, Volume 6: High-Performance Home 

Technologies: Solar Thermal & Photovoltaic 

Systems” (DOE 2007) is available at 

www.buildingamerica.gov.

August 2011 27

27

ENERGY RENOVATIONS HVAC
2.6.2 Active Solar Heating

Active solar heating uses solar collectors that heat water or air. The 

most common are solar thermal water heaters. These are typically 

used for heating domestic hot water. If you are planning to install 

a solar thermal water heater and have or are considering installing 

a hydronic heating system, you can check with your installation 

contractor on the feasibility and cost-effectiveness of connecting the 

solar water heating system with the hydronic heating system to heat 

or preheat the water. 

Another form of active solar heating equipment is a room air 

heater which uses an exterior wall- or roof-mounted flat plate 

collector to heat air that is drawn from the room, passes through 

the collector, and is redistributed to the room. Combination systems 

are also becoming available that draw heated air from underneath 

roof-mounted photovoltaic panels to heat air and/or water via 

heat exchangers located in the attic. More information on active 

solar heating is available at www.energysavers.gov/your-home/

space_heating_cooling. Costs vary depending on system type, size, 

and components. Rebates are available: see www.dsireusa.org.

Solar thermal panels on the roof heat a water-antifreeze solution that is piped 

through a heat exchanger inside a water tank to heat or preheat water that can be 

used for room heating and household hot water.

28 August 2011

ENERGY RENOVATIONS HVAC
3.0 Cooling Systems 

Air conditioning and other manufactured cooling systems are used 

throughout most of the country. This chapter describes typical 

cooling technologies, including air conditioning, heat pumps, 

evaporative cooling, radiant floor cooling, and dehumidifiers. 

However, with home improvements such as air sealing and 

insulating, in some climates home cooling needs can be met 

naturally, without the use of air conditioners, so fans, ventilation 

and passive cooling strategies are also described. 

In moderate climates in a well-insulated home, passive cooling 

strategies like shading, low-solar heat gain windows, and radiant 

barriers can be combined with ceiling fans, ventilation, and 

dehumidification to eliminate or limit the need for air conditioning. 

These techniques should be considered before installing a new air 

conditioning system. See Section 3.7 for more information about 

natural cooling strategies, including the use of fans, night cooling, 

and passive cooling design techniques.

Many types of air conditioning systems are available, including 

central ducted air conditioners, room air conditioners, and heat 

pumps (both ducted and ductless). Evaporative coolers and radiant 

cooling are options in dry climates. 

Over the past few decades, cooling systems have become much 

more efficient. In 2006, the federal government raised the minimum 

efficiency level for residential cooling equipment from SEER 10 to 

SEER 13. Heat pumps are more efficient than standard electric air 

conditioning and new models of ductless heat pumps offer SEER 

ratings as high as 26 at a wide outdoor temperature range. 

In the United States, 61% of households 

have a central cooling system (EIA 

2011). Nearly all new homes are built 

with central air conditioning. Energyefficient alternatives are available.

August 2011 29

29

ENERGY RENOVATIONS HVAC
The following sections describe the advantages and disadvantages 

of typical mechanical cooling systems and recommendations for 

maximizing the efficiency of your new system while reducing upfront 

costs. A contractor can help you determine which system is best for 

your home.

Your choice will likely be influenced by the age and condition of your 

current system, the climate zone, cost, other remodeling activities, 

and energy-efficiency goals. Here are some things to consider. 

• If you have a central air conditioning system, existing ductwork 

might be reused but have the duct system inspected before 

assuming it is usable. The ducts may have been installed poorly, 

gotten damaged over time, or be incorrectly sized for a new system. 

For more information about ducts, see Section 2.1.3.

• If you have a furnace but don’t have central air conditioning, it 

may be possible to incorporate it with your existing ductwork, 

depending on cooling load and sizing.

• If you do not have ductwork, installing ducts in an existing 

home may not be worth the cost (unless you are also installing a 

central furnace). Ductless mini-split heat pumps may be a good 

alternative. 

• If you only plan on cooling sections or additions to your home, 

ductless heat pumps work well for zone cooling. Alternatively, 

window unit air conditioners can be used to cool individual rooms. 

Look for energy-efficient models. 

• If you live in a moderate climate, see Section 3.7 for passive 

cooling strategies.

The decision tree in Figure 3.1 and the cooling systems characteristics 

listed in Table 3.1 may also help you in your decision-making process. 

Table 3.1 presents details on the most common of the cooling systems 

discussed in this chapter, including an indication of cost. It also gives 

the Federal minimum efficiency rating (if established), the minimum 

ENERGY STAR efficiency criteria, and a range of efficiency 

levels for high-performing models you should look for if you are 

purchasing a new system. 

Cooling Efficiency

The cooling efficiency of air 

conditioners and heat pumps is referred 

to as the Seasonal Energy Efficiency 

Ratio (SEER). SEER is a measure of 

equipment energy efficiency over the 

cooling season. It represents the total 

cooling of a central air-conditioner or 

heat pump (in Btus) during the normal 

cooling season as compared to the total 

electric energy input (in watt-hours) 

consumed during the same period. 

Cooling efficiency can also be 

measured by the Energy Efficiency 

Ratio (EER). The EER is a measure of 

the instantaneous energy efficiency of 

cooling equipment. EER is the steadystate rate of heat energy removal (e.g., 

cooling capacity) by the equipment in 

Btu per hour divided by the steady-state 

rate of energy input to the equipment in 

watts. This ratio is expressed in Btu per 

hour per watt (Btu/hr/watt). EER is used 

for room units, while SEER is used for 

centralized units.

The current minimum standard for air 

conditioner and heat pump cooling 

efficiency is SEER 13; this went into 

effect January 23, 2006. Prior to that, 

the minimum efficiency mandated by 

the federal government was SEER 10 

which took effect in 1992. The standard 

is scheduled to be revised by DOE in 

2011, with new requirements becoming 

effective in 2016. 

30 August 2011

ENERGY RENOVATIONS HVAC
 See ductless heat pumps 

and other cooling options.

See passive strategies to 

reduce cooling load.

Should I install a new central air conditioning system?

Replace with new central AC 

or heat pumps.

See passive strategies to lower 

cooling load.

No

Yes

Yes

Yes

2006 or newer 

(≥ SEER 10)

Replace with new 

central AC or heat pump.

No

Yes

Yes

 Pre 2006 (< SEER 10)

Have ducts inspected and air sealed 

or repaired if needed. See passive 

strategies to reduce cooling load.

See central AC 

and heat pumps.

See passive strategies to 

reduce cooling load.

No Yes

Do you currently have 

central air conditioning?

Are you in a 

hot climate?

Are you 

planning to install 

central AC with ducts?

How old is it?

Is it working?

Do you plan 

to keep your central 

heating system 

and ducts?

Will repair cost more than half 

the cost of replacement with 

new system?

Are you adding 

an addition or converting 

unconditioned attic or basement 

into conditioned space?

No

Yes

See passive strategies 

See heat pumps

See passive cooling 

strategies

Repair air 

conditioning system.

Have ducts inspected 

and air sealed or 

repaired if needed. 

See passive strategies to 

reduce cooling load.

No

Figure 3.1. Basic Decisions for Replacing Your Cooling System

August 2011 31

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ENERGY RENOVATIONS HVAC
Table 3.1. Common Cooling Systems Options

Fuel Type Cost* Ducts 

or No 

Ducts?

Central 

or Room 

Cooling

Operates 

as 

Heater in 

Winter

Federal 

Minimum 

Efficiency 

Req

Efficiency 

Range 

for highperforming 

models

Energy 

Star 

Minimum 

Efficiency

CEE Minimum 

Efficiency†

Ducted Central 

AC (Split)*

Electricity Medium Ducts Central No SEER 13 SEER 14.5-20, 

EER 9-15

SEER 14.5, 

EER 12

Tier 1: 

 14.5 SEER, 12 EER; 

Tier 2: 

 15 SEER, 12.5 EER;

Tier 3: 

 16 SEER, 13 EER

Room Air 

Conditioning

Electricity Low No 

Ducts

Room No EER 9.8 EER 10.7-12 10.7 

EER***

9.8-11.8 EER ††

Air-Source Heat 

Pump

Electricity MediumHighDucts Central for 

Air-Source 

HP

Yes SEER 13 SEER 14.5-22, 

EER 9-14

SEER 14.5, 

EER 12

Tier 1: 

 14.5 SEER, 12 EER; 

Tier 2: 

 14.5 SEER, 12 EER; 

Tier 3: 

 15 SEER, 12.5 EER

Ground-Source 

Heat Pump

Electricity Very 

High

Ducts Central Yes -- EER 8.7-23** EER 14.1 Closed-loop 14.1 EER; 

Open-loop 16.2 EER; 

Direct Expans. 15 EER; 

With Desuperheater

Ductless Heat 

Pump

Electricity High No 

Ducts

Room for 

Ductless

Yes SEER 13 SEER 14.5-26 SEER 14.5, 

EER 12

Tier 1: 

 14.5 SEER, 12 EER; 

Tier 2: 

 14.5 SEER, 12 EER; 

Tier 3: 

 15 SEER, 12.5 EER

*Estimated typical installed costs; does not include adding or repairing ducts. Low: $1,500 or less; Medium: $1,500-$4,500; 

High: $4,500-$10,000; Very High: $10,000 or more (www.energysavers.gov).

**This is the ENERGY STAR level for closed-loop water-to-air systems. Find minimum EERs for other configurations at EnergyStar.gov.

***This is the ENERGY STAR level for window units with louvered sides and capacities between 14,000-19,999 Btu/Hr. Find

minimum EERs for other configurations at EnergyStar.gov.

†CEE is the Consortium for Energy Efficiency, www.cee1.org

††Depends on air conditioner size: 

>8,000 Btu/hr: Tier 1–11.2 EER, Tier 2–11.6 EER 

8,000–13,999 Btu/hr: Tier 1–11.3 EER, Tier 2–11.8 EER 

14,000-19,999 Btu/hr: Tier 1–11.2 EER, Tier 2–11.6 EER 

>20,000 Btu/hr: Tier 1–9.8 EER, Tier 2–10.2 EER

Seasonal Energy Efficiency Ratio (SEER): SEER is a measure of equipment energy efficiency over the cooling season. It represents the total 

cooling of a central air conditioner or heat pump (in Btu) during the normal cooling season as compared to the total electric energy input (in 

watt-hours) consumed during the same period.

Energy Efficiency Ratio (EER): EER is an efficiency rating for room air conditioners based on how many Btus of heat per hour the unit can 

remove for each watt of power it draws. This ratio is expressed in Btu per hour per watt (Btu/hr/watt).

32 August 2011

ENERGY RENOVATIONS HVAC
Compressor

Heat

Removed

from

Indoor

Outdoor Unit

Refrigerant 

Piping

Cooled Supply 

Air

Evaporator Coil

Furnace

Filter

Warm

Return Air

Condensor Coil

House Wall

HVAC Register HVAC Register

3.1 Central Air Conditioning 

Central air conditioning provides cooled air throughout your house. 

Central air conditioners are typically installed with central furnaces 

and use the same ducts and blower. Refrigerant is piped to the 

evaporator coil in the air handler unit where it cools the distribution 

air. Central air conditioners are generally more efficient than room 

air conditioners, so if you plan on cooling the majority of your 

house, a central air conditioner can save energy and money. 

Air conditioners have become much more efficient over the past few 

decades. Technology improvements include variable-speed motors 

that allow more control over air distribution, which can lower energy 

consumption and increase comfort. The majority of systems rated 

SEER 15 or higher incorporate variable-speed motors to achieve this 

efficiency. Advanced compressors and micro-channel heat exchangers 

are other advancements that have improved efficiency.

If your existing air conditioner is a pre-2006 model, a new unit could 

reduce your cooling costs by 20% to 40% (DOE 2010). Central air 

conditioning systems are rated according to their seasonal energy 

efficiency ratio (SEER). Look for units with high SEER ratings to 

maximize your energy savings over the course of the cooling season. 

Since 2006 the federal government has required new air conditioners 

sold in the United States to have a SEER rating of 13 or higher. 

However, many older systems have much lower SEER ratings. Split 

system air conditioners (the most common in homes) can use the 

ENERGY STAR label if their SEER is 14.5 or greater. The best 

available air conditioning units can have SEER ratings of over 20.

Sizing up old Air Conditioners

Air conditioners are sized by their 

capacity in terms of tons. One ton 

equals 12,000 Btu of cooling capacity. 

Not sure of the current size of your air 

conditioner? Look at the name plate 

on the outdoor condensing unit and 

locate the model number (not the serial 

number). You are looking for two digits 

in the model number that match the 

numbers below to indicate tons or Btus. 

18 = 1.5 Ton (18,000 Btu/hr)

24 = 2 Ton (24,000 Btu/hr)

30 = 2.5 Ton (30,000 Btu/hr)

36 = 3 Ton (36,000 Btu/hr)

42 = 3.5 Ton (42,000 Btu/hr)

48 = 4 Ton (48,000 Btu/hr)

60 = 5 Ton (60,000 Btu/hr)

For example, a model SSX160241 is a 

2-ton (24,000 Btu) air conditioner.

Central air conditioning equipment shares the air handler cabinet and duct 

distribution system with the furnace.

Register design can have a big impact on 

the comfort of central heating and cooling 

systems. 

August 2011 33

33

ENERGY RENOVATIONS HVAC
Table 3.2 lists the potential energy cost savings from switching to a 

high-efficiency unit per $100 spent on cooling costs. For example, if 

you currently spend $400 per year on cooling costs (what the typical 

family spends annually on cooling in warm climates [EIA 2008]) 

and you switch from a SEER 10 unit to a SEER 15 unit, you will 

save about $132 per year. Studies indicate that if you upgrade from 

a SEER 9 unit to a new SEER 15 unit you can save 35% in cooling 

costs; if your air conditioner is a SEER 6 and you upgrade to a 

SEER 15, savings could be as high as 51%. Savings will be higher 

if you are in a hot climate. Annual savings will increase over time if 

utility rates rise. 

Table 3.2: How Much You'll Save When You Increase 

Your Cooling Equipment Efficiency 

Annual Estimated Savings for Every $100 of Costs.

(Source: www.energysavers.gov) 

Existing 

System SEER

New/Upgraded System SEER

13 14 15 16 17 18 19 20

10 $23 $29 $33 $38 $41 $44 $47 $50

11 $15 $21 $27 $31 $35 $39 $42 $45

12 $8 $14 $20 $25 $29 $33 $37 $40

13 - $7 $13 $19 $24 $28 $32 $35

14 - - $7 $13 $18 $22 $26 $30

15 - - - $6 $19 $17 $21 $25

16 - - - - $6 $11 $16 $20

3.1.1 Repair or Replace?

High-efficiency units can cost more than units with the minimum 

required SEER (ConsumerSearch Inc. 2008) but should pay for 

themselves over time (see “air conditioning” at www.energystar.gov 

for a payback calculator). Talk to your contractor about costs and 

savings in comparison to heat pumps.

Your contractor can give you recommendations for getting the most 

out of a new or existing central air conditioning system: 

• SIZING – Your air conditioner should be properly sized using 

ACCA’s Manual S. If you have improved the efficiency of your 

house, it may be possible to select a smaller size when replacing 

your unit or to replace two central units with one central unit, 

recouping part of your investment in energy efficiency. Oversized 

air conditioners will cycle on and off frequently, decreasing 

efficiency and increasing maintenance costs. Frequent cycling 

means that oversized units do not dehumidify as well as properly 

sized units (an important consideration for humid climates). 

Bigger is not always Better 

Your old air conditioner may be 

oversized. An overly large system 

will blast on quickly, bringing the air 

temperature below the set point and 

shutting off before it has had time to 

remove moisture from the air, which 

can be a problem where summers are 

humid. Contractors sometimes oversize 

central air conditioners because 

they use rules of thumb rather than 

performing load calculations. The 

contractor should use ACCA Manual J to 

calculate your cooling load and ACCA 

Manual S to correctly size your new 

central air conditioning system (ACCA 

2005; 1995). This is especially important 

if you have done significant air sealing 

and insulating, which will reduce your 

heating and cooling load. (The ACCA 

has produced two 2-page brochures 

for contractors on using Manual J and 

Manual S. See ACCA 2011 b, c) Note 

that central air-to-air heat pumps may 

require some oversizing to perform 

adequately because they typically do 

not supply as much cooling per air 

volume as a standard air conditioner. 

Also oversizing is less of an issue with 

some of the latest heating and cooling 

equipment that has variable speed 

motors and compressors, which can 

operate at lower speeds and capacities 

that better match low demand times, 

while having the ability to increase 

capacity when demand spikes. 

34 August 2011

ENERGY RENOVATIONS HVAC
• AIR CONDITIONER SETTINGS – The time-delay relay on 

many newer air conditioning units is set to keep the fan running 

for about two minutes after the compressor shuts off. The relay 

can help boost efficiency in dry climates, but allows some of the 

moisture on the evaporator coil to evaporate back into the air 

stream, contributing to indoor humidity in humid climates. The 

time-delay relay is typically jumper selectable and should be set to 

30 seconds or less in humid climates. Also, the fan on central air 

conditioning systems should always be set to “Auto” rather than 

“On” for the most efficient operation. Set the compressor to start 

before the blower. Make sure the drain pans are correctly installed.

• ZONING – Your contractor may recommend two or more air 

conditioners to provide zoning of separate floors of a multi-story 

house. Dampered zoning has some performance issues, including 

noise and difficulty maintaining flow over the coil.

• ECONOMIZERS – In dry climates, take advantage of night-time 

cooling with economizers that draw in outside air during evening 

and early morning hours (McWilliams and Walker 2005). 

• FILTERS – Building America recommends using filters that 

are rated MERV 8 or higher in new furnaces that are built to 

accommodate 2-inch to 4-inch thick filters. In older air handlers 

that have 1-inch filter slots, high-MERV 1-inch filters may block 

air flow; it may be preferable to use lower MERV filters that 

are replaced more often, even monthly, when the air handler is 

running often. 

• REFRIGERANT CHARGE – The level of refrigerant may be too 

low (undercharged) because of leaks or too high (overcharged) 

because the installer added too much. One study found that in a 

system that was undercharged by 20%, the efficiency dropped by 

about 21%. Likewise, in a system that was overcharged by 20%, 

the efficiency dropped by about 12% (Farzad and O’Neal 1998). 

The EPA reports that 75% of installed air conditioners had the 

wrong amount of refrigerant when tested. Incorrect refrigerant 

levels can lower efficiency by 5% to 20% and can cause premature 

component failure, resulting in costly repairs (see EPA Heating 

and Cooling Refrigerant Charging guidelines at www.epa.gov).

• TEST AIR FLOW AND DUCT LEAKAGE – Improper air flow 

and leaking ducts can significantly affect the performance and 

efficiency of your system. The only way to know if you have a 

blocked or disconnected duct, big air leaks, or inadequate air flow 

is to test your ducts with duct leakage and air flow tests. 

Have your refrigerant charge checked by 

a certified HVAC technician. Under- and 

over-charged systems can affect the 

system’s efficiency and cause premature 

component failures.

ANSI/ACCA HVAC Standards

The Air Conditioning Contractors 

of America has produced several 

American National Standards Institute 

(ANSI) approved standards on HVAC 

equipment installation and maintenance 

including

• ANSI/ACCA Standard #4 Maintenance of 

Residential HVAC Systems (ACCA 2010a)

• ANSI/ACCA Standard #5 HVAC Quality 

Installation Specification (ACCA 2010b)

• ANSI/ACCA Standard #6 Restoring the 

Cleanliness of HVAC Systems (ACCA 

2010c)

• ANSI/ACCA Standard #9 Quality 

Installation Verification (ACCA 2010d).

August 2011 35

35

ENERGY RENOVATIONS HVAC
3.2. Room Air Conditioning

Window and through-the-wall air conditioners are used to cool 

single rooms or small zones within a house. They typically have a 

lower efficiency than central AC systems. Window units often lack 

insulation and air sealing around them because they are usually 

temporary installations; therefore, using them is not considered an 

energy-efficient best practice. However, room air conditioners will 

cost less to purchase and install than a central AC system, and there 

may be some energy savings if you only plan to cool a small part of 

your house.

If you choose to install a room air conditioner for zone cooling, 

find a unit with an EER of 10 or more. Properly size the unit to 

the space because oversized units will cycle on and off frequently, 

affecting their ability to reduce humidity levels. Direct sunshine on 

the outdoor components can reduce efficiency by as much as 10%, so 

ideally window units should be installed in a shady area on the north 

or east side of the house (DOE 2010). Room air conditioners may be 

an effective solution if air conditioning is rarely called for. However, 

if air conditioning is desired on a daily basis for most of the cooling 

season, consider investing in a ductless heat pump.

3.3 Heat Pumps 

Standard air-source heat pumps, ground-source heat pumps, and 

ductless mini-split heat pumps all provide cooling as well as heating. 

Heat pumps also dehumidify like air conditioners. 

3.3.1 Central- and 

Ground-Source Heat Pumps

Central air-source heat pumps and ground-source heat pumps are 

described in Section 3.0. Efficient centralized heat pumps have a 

SEER of 15 or more; very efficient heat pumps can have a SEER of 

18 to 21. Ground-source heat pumps can achieve efficiencies of 300%.

3.3.2 Ductless Heat Pumps

Ductless heat pump technology was described in Chapter 2. Ductless 

heat pumps save energy and money because they can be used for 

zone cooling (only cooling parts of the house) and because they 

avoid the large fan energy and duct losses typically associated with 

central ductwork. The advanced inverter technology incorporated 

into these units has also increased their efficiency at a wider 

Room Air Conditioner 

Efficiency Ratings

The efficiency of window units is 

measured by their energy efficiency 

ratio (EER, the ratio of cooling capacity 

in Btu/hour to power input in watts). 

Minimum Federal standards were 

first established in 1987 and became 

effective in 1990. The requirement varies 

by unit size and type, but for the most 

common type (an 8,000–13,999 Btu/

hour unit with side vents) the 1987 law 

required an efficiency of 9.0 EER. This 

was revised by the Federal government 

to 9.8 EER effective October 2000. DOE 

is required to publish a new standard by 

June 2011, to be effective in 2014, and an 

EER of 11.0 is being considered. ENERGY 

STAR specifications were last updated 

in 2001 and specify a 10.8 EER for the 

most common units. Specifications 

for ENERGY STAR Version 3.0 

were due in May 2011 and will be 

effective in February 2012 (ACEEE 

www.standardsasap.org/products/

room_ac.html).

Components of a room air conditioner. 

(DOE 2010)

36 August 2011

ENERGY RENOVATIONS HVAC
Expansion 

Valve

Indoor Coils 

Condenser

Gas condenses 

into a liquid, 

releasing 

heat inside

Gas condenses 

into a liquid 

releasing heat 

to the outside

Compressor

Liquid evaporates

into gas 

pulling heat 

from the inside

Fan

Indoor Coils

Evaporator

Expansion 

Valve

Outdoor Coils

Condenser

Air-Source Heat Pump Cooling Cycle -

In cooling mode, an air-source heat pump 

evaporates a refrigerant in the indoor 

coil. As the liquid evaporates, it pulls heat 

from the air in the house. After the gas is 

compressed, it passes into the outdoor 

coil and condenses, releasing heat to the 

outside air. The pressure changes caused 

by the compressor and the expansion 

valve allow the gas to condense at a high 

temperature outside and evaporate at a 

lower temperature indoors. 

Air-Source Heat Pump in Cooling Cycle

temperature range so that backup heating is unnecessary. Ductless 

heat pump models are available with SEER ratings as high as 26. 

Ductless mini-splits generally cost about 30% more than central 

heat pumps, not including the cost of ductwork for central systems 

(DOE 2010). However, if you would need to install ducts to add a 

central AC system to your home, the ductless mini-split heat pumps 

may be a less expensive option up front. Ductless heat pumps are a 

good option for additions. 

Ductless mini-split air conditioning systems, which provide cooling 

but not heating, are also available. Mini-split AC systems could be 

an option in houses that use a non-ducted heating system that you 

aren’t ready to replace.

3.3.3 Absorption Heat Pumps

Absorption heat pumps, sometimes called gas-fired heat pumps, 

are essentially air-source heat pumps driven not by electricity, 

but by a heat source such as natural gas, propane, solar-heated 

water, or geothermal-heated water. The cooling version is called 

an absorption cooler or gas-fired cooler. It works on the same heat 

pump principle but is not reversible and cannot serve as a heat 

source as well.

Although mainly used in industrial or commercial settings, 

absorption coolers are now available for large homes (4,000 ft2

or more). Absorption heat pumps for smaller homes are being 

developed. Absorption coolers and heat pumps have lower 

efficiencies than other heat pumps (1.2+ COP for heating; 0.7+ COP 

for cooling), but they can make use of solar energy, geothermal 

hot water, or other heat sources and may be cost-effective where 

electricity rates are very high. 

August 2011 37

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ENERGY RENOVATIONS HVAC
3.4 Evaporative Coolers

Evaporative coolers can be an effective and less expensive alternative 

to compressor-based air conditioners for cooling your home if you 

live in a dry climate. Evaporative coolers (known in the past as 

swamp coolers) use evaporation and blowing air to cool. They can 

use about one-quarter as much energy as central air conditioners 

and cost half the price. Evaporative coolers require regular 

maintenance to keep the water reservoir clean.

Today’s evaporative coolers come in one of three general designs: 

direct, indirect, and indirect/direct.

Direct, single-stage evaporative coolers work by drawing outside 

air through water-saturated pads. The flowing air evaporates some 

of the water, giving up heat in the process, which can reduce the 

air temperature by 15°F to 40°F. The cooled, humidified air is then 

blown into the home. The air is not recirculated inside the house 

but is blown through the house and an exit must be provided for 

it; thus, a window or vent must be opened to allow air to leave the 

house. Lower air flow helps the cooler to work more efficiently. An 

evaporative cooler should have at least two speeds and a vent-only 

option. The vent-only operation allows the unit to be used as a 

house fan during mild weather. 

Indirect coolers use an air-to-air heat exchanger so they don’t add 

humidity to the cool air. The main fan supplies outside air that is 

cooled by passing through the heat exchanger into the home. A 

second fan draws exhaust air from the home and/or outside air 

through the wet pads, which are in contact with the heat exchanger 

and cool it without raising the humidity of the air that flows into 

the home. 

Evaporative

Pad

Blower

Water Distribution Lines

Recirculating Water Pump

Float

Outside Air

Outside Air

Cool Air 

to House

Blower

Motor

This evaporative cooler mounts on an 

exterior wall of a home built by Community 

Development Corporation of Utah with 

design assistance from Building America's 

Consortium for Advanced Residential 

Buildings (CARB) research team (Source: 

Steven Winter Associates).

Evaporative Coolers

Direct evaporative coolers consist of a 

fan surrounded by thick pads that are 

continually soaked with sprayed water. 

As the fan pulls outside air through the 

pads, the water absorbs heat from the air 

and evaporates, which lowers the dry bulb 

temperature of the incoming airstream. 

The cooled air is blown into the house 

through a short duct to direct the cold 

air to the home’s main living area. Two 

advanced forms of evaporative coolers 

are now available. Indirect coolers use an 

air-to-air heat exchanger so they don’t add 

humidity to the cool air. Indirect/direct 

coolers use a heat exchanger to precool 

the air then pass it through the direct 

cooling stage which further cools and 

humidifies the air.

38 August 2011

ENERGY RENOVATIONS HVAC
Hot 

fluid out

Cold 

fluid in

Indirect/direct coolers cool in two stages. In the first stage, the air 

passes through an indirect cooler, which lowers the temperature 

without adding humidity. The air then enters the second, direct 

cooling stage where it flows through the wet pads to be further 

cooled and humidified before flowing into the home. One model, 

developed by Building America partner Davis Energy, reportedly 

provides up to 5 tons of cooling while using less than 1600 watts. 

The model is eligible for utility rebates up to $1,100 in several 

south-western states. The installed cost for an efficient indirect/direct 

evaporative cooler is similar to or less than that of a new central 

air conditioning system (Eastment et al. 2005). Evaporative coolers 

do use water and water costs should be included when considering 

installing an evaporative cooler.

Another innovative evaporative technology is the water-cooled 

evaporative condenser, which is a scaled-down residential version 

of the 250-ton chillers used on commercial buildings. Inside the 

housing, a mist of water is continually sprayed on the condenser 

coils to remove heat from the refrigerant and at the same time reduce 

the work of the compressor. Unlike traditional air conditioners, 

which use 10% more power for each 10° F increase in temperature 

above 95° F, an evaporative-cooled condenser draws about the same 

power over a wide range of outdoor temperatures. It uses about half 

the energy costs of conventional “air-cooled” condensing units. One 

model has an EER of 17 at 95°F.

There are now evaporative coolers on the market that use 

photovoltaic (PV) panels to create the electricity used to run the 

blower and the water pump. For hot, desert areas, the combination of 

evaporative cooling and solar power is a perfect match: the afternoon, 

when the most solar energy is available, is also the hottest part of the 

day, when cooling is most needed. And, because evaporative coolers 

use a fraction of the energy of air conditioners, PV cells can provide 

enough electricity to run the system effectively (CEC 2011).

3.5 Radiant Cooling

Ground-source heat pumps can be used to provide radiant cooling 

as well as heating. Closed-loop systems circulate cool water through 

tubes in the floor, ceiling, or wall panels, cooling living spaces as 

they absorb heat, which is transported and released through loops in 

the ground or in cooling ponds. While radiant heating has been well 

received, radiant cooling is problematic due to comfort issues (bare 

feet on cold floors) and condensation issues in rugs and carpets. 

Because of the moisture issues, radiant cooling is only recommended 

in dry climates. For more on this technology, see Section 2.4.2.

Ground-source heat pumps can provide 

cool water for radiant floor cooling in hot 

dry climates.

August 2011 39

39

ENERGY RENOVATIONS HVAC
3.6 Dehumidifiers 

In hot, humid climates, there are times of the year, especially in the 

spring and fall, when the temperature is not high enough to call 

for air conditioning, but the humidity level is high enough to make 

conditions inside the home uncomfortable. At times like these, a 

dehumidifier can bring the humidity down to a comfortable level, 

without the need for air conditioning. 

One study done by Building America partner Building Science 

Corporation in Houston, Texas (Rudd et al. 2005) indicated that 

separate dehumidification is even more necessary in energy-efficient 

homes because efficiency measures like better insulation, air sealing, 

and energy-efficient windows reduce the home’s temperature but 

don’t reduce humidity. Also, in an energy-efficient home, a central 

air conditioning system does not have to operate as much to bring 

the indoor temperature down. Therefore, the air conditioner may 

not operate long enough to reduce the humidity, especially in the 

spring and fall when outdoor temperatures are not much higher 

than indoor temperatures. The study also compared dehumidifier 

technologies and found that stand-alone dehumidifiers were a costeffective option compared to more expensive, integrated systems.

Before installing a dehumidifier, your contractor will rule out 

other sources of moisture in the home that need to be repaired. 

This could include a dirt basement or crawlspace floor that is not 

covered with a plastic vapor barrier, open sump pumps, improper 

site grading that allows water to pool around the foundation, 

inadequate exhaust ventilation, or exhaust fans that vent to the attic 

(Cummings et al. 2011).

Dehumidifiers can be ducted to a 

furnace or heat pump central air 

handler. Dehumidifiers, air handlers, and 

ducts perform best when installed in 

conditioned spaces. This dehumidifier 

and air handler were installed in the 

insulated attic of a a high-performance 

home built by KB Home in Orlando, 

Florida (Source: FSEC).

40 August 2011

ENERGY RENOVATIONS HVAC
3.7 Natural Cooling Strategies 

In a well-insulated home in a moderate climate, summer heat may be 

adequately controlled by ventilation and dehumidification, combined 

with passive cooling strategies, such as low-solar heat gain windows, 

shading, cool roofs, and radiant barriers to minimize summer solar 

heat gain. Through the energy assessment, your contractor can help 

you determine whether your home needs additional air sealing and 

insulation. Once these things are done, and before installing a central 

air conditioning system, consider the following strategies.

3.7.1 Fans and Ventilation for Cooling

Natural and fan ventilation strategies can be the least expensive 

and most energy-efficient way to cool buildings. Fans works best in 

moderate to cool climates, in climates where temperatures drop at 

night, and in climates that are not excessively humid. In hot, humid 

climates where temperatures stay warm through the night and 

outdoor air remains humid through most of the summer, ventilation 

alone may not be enough to control the heat and you may want to 

consider air conditioning. However, even in hot, humid climates, 

ventilation and supplemental dehumidification, combined with the 

heat-avoiding passive cooling strategies discussed below, will reduce 

your air conditioning needs.

3.7.1.1 Central Fan-Integrated Night Cooling 

Fan-integrated night cooling uses your central furnace fan and 

a fresh air intake to draw in cool outside air at night, mix it with 

returning house air, and distribute it through the house. Dampers 

on the fresh air intake can be controlled by temperature sensors 

to open when outside evening or early morning temperatures drop 

below inside temperatures. Humidistat sensors can close the dampers 

if humidity levels outside are too high. The system is most costeffective in dry climates.

This fan-integrated night cooling provides several advantages 

over just opening windows: the incoming outside air can be drawn 

through a filter, it is evenly distributed throughout the home, and 

there is security in not having to leave windows open at night. It is 

best implemented with a variable-speed fan motor that allows lower 

air flow rates and energy savings. This system is further described in 

Chapter 4.0, “Ventilation.”

If you don’t have a central furnace fan, you can still use this concept 

to take advantage of night cooling by having an outside air duct with 

a mechanical damper installed that connects to a centrally located 

exhaust fan installed in reverse to draw air in rather than pull air out. 

Both the fan and the damper can be wired to a temperature sensor.

Night Breeze—

Building America Partner Davis Energy 

Group developed the NightBreeze 

system, an “intelligent” sensorcontrolled system that integrates 

ventilation cooling and fresh air 

ventilation with regular ducted 

central heating and air conditioning 

systems. Studies for the California 

Energy Commission have shown that 

NightBreeze can reduce cooling energy 

costs by about 25%-40% in California 

central valley climates and can eliminate 

the need for air conditioning in coastal 

climates while improving indoor air 

quality and comfort. Unlike whole house 

fans, it filters outdoor air and does not 

require windows to be opened. (Source: 

Davis Energy Group)

Air Intake

Filter

Supply

Air

Return 

Air

Damper Blower 

Unit

Heating & 

Cooling Coil

Heating & 

Air Conditioning Outside 

Air

Air Exhausted

through

Attic Vents

Supply Air Relief Air

Ventilating

Source: Davis Energy Group

Porches, awnings, and windows that open 

to provide cross ventilation can all help 

homeowners take advantage of natural 

cooling strategies to reduce cooling 

energy bills.

August 2011 41

41

ENERGY RENOVATIONS HVAC
3.7.1.2 Natural Draft 

Depending on the location and design of the home, natural 

convection and cool breezes can help cool the home without 

requiring even the aid of mechanical fans. If you are replacing 

windows, determine if picture windows can be replaced with 

windows that open, if they face favorable prevailing breezes. 

If you have a two-story house, you can take advantage of the “stack 

effect.” (You can see this at work in a chimney when air rises through 

the column and out the opening at the top due to air pressure 

differences inside and outside of the chimney.) Windows can be 

opened downstairs at the same time as windows upstairs, or at the 

tops of stairwells, or at openable skylights to draw hot air up and 

out of the house. 

3.7.1.3 Circulating Fans 

Circulating fans include ceiling fans, table fans, and floor fans. These 

fans create a wind chill effect that will make you more comfortable in 

your home, even if it is also cooled by air conditioning. In temperate 

climates, or during warm weather, fans may allow you to avoid using 

your air conditioner altogether. However, be sure to turn off ceiling 

fans when you leave a room; fans cool people, not rooms. If you use 

air conditioning, a ceiling fan will allow you to raise the thermostat 

setting about 4°F with no reduction in comfort. A larger blade will 

also provide comparable cooling at a lower velocity than a smaller 

blade. Check the noise ratings, and, if possible, listen to your fan in 

operation before you buy it.

Turn on the ceiling fan and you can 

raise that thermostat 4 degrees with no 

complaints. Ceiling fans work best when 

the blades are 7 to 9 feet above the floor 

and 10 to 12 inches below the ceiling. Fan 

blades should be at least 8 inches from 

the ceiling and 18 inches from the walls. 

Multiple fans work best in rooms longer 

than 18 feet.

Building America’s research team lead 

Building Science Corporation used 

convection to help cool this structural 

insulated panel (SIP) cottage in Georgia. 

Cool air from the screened porches is 

drawn into the building’s interior where it 

heats up and is pulled up and out by the 

“stack effect" (in the same way that air 

is drawn up a chimney by differences in 

the air pressure inside the chimney and 

outside the chimney). The air flows out the 

second-story windows, drawing more air in 

through the shaded first-story windows.

42 August 2011

ENERGY RENOVATIONS HVAC
3.7.1.4 Window Fans 

Window fans use relatively little electricity and can provide sufficient 

cooling for homes in many parts of the country. Window fans are 

best used in windows facing away from the prevailing wind; the fan 

is installed facing in to pull air out of the house, not push air into 

the house. The window fan will work best if you close windows 

near the fan and open windows at the opposite end of the house. 

If your house is multilevel, put the fan in an upstairs window and 

open windows downstairs at the other end of the house. Windows 

on shaded parts of the house provide the best intake air for cooling. 

When buying window fans, look for ENERGY STAR® rated fans, 

which are 20% more efficient than standard models.

3.7.1.5 Attic Vents 

Ventilating your attic can reduce the amount of accumulated 

heat that would otherwise warm your house and make air 

conditioning equipment installed in the attic work harder. Properly 

sized and placed roof vents help prevent overheating in your attic. 

Ventilated attics are about 30°F cooler than poorly ventilated attics 

(www.energysavers.gov). Electric and solar-powered attic fans that 

mount in gable vents are available, but they are not necessarily 

recommended. They have not been shown to reduce air conditioning 

bills. They can pull air-conditioned air out of your home and into 

your attic if the ceiling of your home is not well air sealed.

3.7.1.6 Whole House Fans

If you live in a dry, moderate climate with a large day-to-night 

temperature difference, a whole house fan might be worth 

considering for home cooling. Whole house fans are located in the 

ceiling of a centrally located area on the upper floor of your home. 

(Install in the second-story if you have a two-story home.) The fan 

is operated with lower-floor windows open. Your attic must be well 

ventilated with ridge and/or gable vents. Whole house fans draw 

air through the house and push it out through your attic. Whole 

house fans can quickly cool your house at night, once the outside 

temperature has dropped. 

The fans are large and can be loud, especially if they are poorly 

designed. Also, be cautious and avoid running the fan while 

combustion equipment (like a natural-draft water heater) is running. 

Combustion equipment may backdraft when the fan turns on, if not 

enough windows are open. Whole-house fans are not recommended 

in humid climates, because they pull in humid air and add humidity 

to the attic. They may not be appropriate in areas where opening 

first-floor windows at night would cause security concerns. When 

not in use the fan should be covered from the attic side with a tightfitting, gasketed, insulated cover.

Window fans pull hot air out of the home.

August 2011 43

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ENERGY RENOVATIONS HVAC
3.7.2 Passive Cooling 

Passive cooling refers to use of the home’s design to keep the home’s 

interior cool. While the best time to incorporate passive design 

is in the home’s initial construction, many passive strategies can 

be incorporated in common remodeling projects. These include 

upgrading windows, adding shading, replacing roofing with cool 

roof materials, and installing radiant barriers.

3.7.2.1 Windows 

NEW WINDOWS – While energy-savings alone won’t necessarily 

justify the purchase of high-performance windows, if you are 

already planning to replace your windows, invest in energy-efficient 

windows that meet the ENERGY STAR criteria. A contractor can 

help you determine which windows are best for your climate zone, 

using window ratings such as the solar heat gain coefficient (SHGC) 

and the U-factor. 

SHGC is a measure of how well the window blocks heat caused 

by sunlight. Look for windows with a lower SHGC if you live in 

a warm climate. U-factor is a measure of how well the window 

performs at stopping heat flow. Look for windows with a lower 

U-factor (the lower the U-factor, the better).

Your contractor will likely recommend ENERGY STAR-certified 

windows. ENERGY STAR ratings for windows vary based on the 

climate you live in. The current minimum specification for ENERGY 

STAR windows in southern climates is less than or equal to 0.27 

SHGC and less than or equal to ≤ 0.60 U-factor. In northern 

climates, the current minimum specification for ENERGY STAR 

windows is a U-factor of less than or equal to 0.30; the SHGC is not 

specified because solar heat gain is desirable for much of the year in 

cold climates. 

In warm climates, look for windows manufactured with spectrally 

selective low-emissivity coatings. These super-thin, virtually invisible 

metal coatings block heat gain but allow most visible light to come 

through. 

For more information about windows, see the DOE-sponsored 

Efficient Windows Collaborative website at www.efficientwindows.org. 

When window shopping, check the label 

for energy efficiency or look for ENERGY 

STAR-rated windows.

Window Ratings

• Solar Heat Gain Coefficient measures 

the fraction of solar energy transmitted 

and tells you how well the product 

blocks heat caused by sunlight. SHGC 

is measured on a scale of 0 to 1; values 

typically range from 0.25 to 0.80. The 

lower the SHGC, the less solar heat the 

window transmits.

• The Shading Coefficient (SC) describes 

how much solar energy is transmitted 

through a window compared to a clear 

single glass, which has an SC of 1.0. The 

lower the number, the less solar heat 

will enter your home and the lower 

your cooling bills will be. For example, 

a window treatment with a shading 

coefficient of 0.40 will prevent about 

60% of the solar heat gain while a 

shading coefficient of 0.3 will block out 

about 70%.

• U-Factor (U-value) measures the rate 

of heat transfer and tells you how well 

the window insulates. U-factor values 

generally range from 0.25 to 1.25 and are 

measured in Btu/hr·ft2·°F. The lower the 

U-factor, the better the window insulates.

• Visible Transmittance (VT) measures 

the amount of light the window lets 

through. VT is measured on a scale of 0 

to 1; values generally range from 0.20 to 

0.80. The higher the VT, the more light 

you see.

44 August 2011

ENERGY RENOVATIONS HVAC
EXISTING WINDOWS – If you are keeping your existing windows, 

there are some steps you can take to reduce how much heat they 

let in. On south- and west-facing windows, you can install sun 

screens that have small aluminum louvers, fiberglass mesh, or tough 

metalized polyester film laminated to vinyl. Such removable shade 

screens can be taken down to allow you to take advantage of the 

sun’s heat during the winter.

You can also reduce heat from the sun by applying window-tinting 

films. One problem with these films is that they can reduce the clarity 

of the glass; they may also need to be reapplied. However, such 

treatments and shades are much less expensive than new windows.

3.7.2.2 Shading 

According to the U.S. Department of Housing and Urban 

Development, stopping the sun’s heat before it penetrates windows 

and sliding glass doors is up to seven times more effective than using 

interior blinds or curtains (APS 2009).

Exterior shading options include trees, porches, awnings, pergolas, 

trellises, working shutters. If your remodeling project includes 

changing the roofline, include overhangs in your design, especially 

on south-facing walls. Overhangs protect windows and walls from 

heat gain and ultraviolet radiation, as well as rain, hail, and snow. 

Optimal overhang dimensions for blocking summer sun while 

allowing winter sun to come in can be calculated at www.susdesign.

com/overhang/index.php. 

Mature, well-placed trees can reduce 

cooling costs by 5% to 10%.

Careful landscaping can preserve rooftop solar exposure for solar panels and 

provide shading to help control solar heat 

gain through windows. Large deciduous 

shade trees on the southwest corner of 

the home provide welcome relief from 

summer afternoon sun while allowing 

desirable winter sun to warm the house 

(Walker and Newman 2009).

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ENERGY RENOVATIONS HVAC
Trees reduce cooling requirements, particularly when located on the 

south and west side of the home, by blocking the peak solar-gain of 

low-angle, late-afternoon sun. Deciduous trees are ideal for summer 

shading in cold climates because their lack of leaves in the winter 

will not block desirable sunshine during the heating season. Studies 

have shown a mature tree canopy can reduce peak July afternoon 

temperatures around a home by 1°F to 3°F, and the total effect of 

shading—lower summer air temperature and reduced wind speed—

can reduce cooling costs by 5% to 10% (McPherson et al. 1994).

3.7.2.3 Cool Roofs

If you are replacing your roof and you live in a hot climate, consider 

replacing it with a cool roof. Cool roofs are white or light-colored 

roofs or roofs made with coatings that have high solar reflectance. 

These roofs reflect back most of the solar energy received, and 

they have high thermal emittance so they are able to radiate back 

absorbed solar heat (Parker and Sherwin 2008). Studies show that 

cooling cost savings of 7% to 15% are possible (www.coolroofs.org). 

Savings will be greater if your heating and cooling ducts are installed 

in the attic.

3.7.2.4 Radiant Barriers

Radiant barriers can be installed in attics to reduce solar heat gain. 

These work well in hot climates where you want to keep heat out 

of the attic but are not recommended in cold climates where heat 

gain is desirable. Sometimes called reflective insulation, radiant 

barriers can come in sheets that consist of a layer of aluminum foil 

with a backing of kraft paper, plastic film, polyethylene bubbles, 

or cardboard. The sheets are stapled to the underside of the attic 

rafters to shield the attic from solar heat gain. The barrier is stapled 

shiny side down with an air gap of at least 3/4 inch between the 

shiny side and the attic insulation below so the radiant barrier 

can work properly. Also available are radiant barriers that come 

factory-adhered to OSB roof sheathing. Research by the Florida 

Solar Energy Center (a Building America team) showed radiant 

barriers can provide cooling energy savings of about 8% to 12%. 

(See the FSEC Radiant Barrier Primer for more information, 

including installation recommendations, http://www.fsec.ucf.edu/en/

publications/html/FSEC-EN-15/). 

Light-colored roofing can help minimize 

heat gain from solar radiation. Reflective 

roofs help keep homes (and surrounding 

neighborhoods) cool and help offset 

carbon emissions.

Radiant barriers can significantly reduce 

solar heat gain through the roof in warm 

climates.

46 August 2011

ENERGY RENOVATIONS HVAC
4.0 Ventilation

Ventilation is needed for good air quality inside your home. 

Ventilation brings in fresh air and removes stale air, including indoor 

contaminants like house cleaning chemicals and off-gassing paints 

and plastics, excess moisture from showering and cooking, and 

pollutants like carbon monoxide and other combustion byproducts. 

Air may be brought in and removed incidentally through air 

leaks or naturally through open windows. Or, it can be brought 

in and removed intentionally through mechanical means. Most 

home heating and cooling equipment, including forced-air heating 

equipment, is not manufactured to bring fresh air into the house and 

expel stale air. To accomplish this, either the heating and cooling 

equipment must be combined with a ventilation system or a separate 

ventilation system must be installed. 

Ventilation equipment can be thought of in three categories: 

exhaust-only, which removes stale air from the house; supply-only, 

which provides fresh air to the house; and balanced systems, which 

do both. These ventilation strategies are described below and are 

described in depth with numerous examples of configuration options 

in the report, Local Exhaust and Whole House Ventilation Strategies, 

prepared by Building Science Corporation for Building America 

(Rudd 2011). Advantages and disadvantages of each strategy are 

summarized in Table 4.1 at the end of this chapter. The best strategy 

for your home depends on several factors, including the climate you 

live in, the air tightness of your home, and what type of heating and 

cooling equipment you have.

How much ventilation do we need? The American Society 

of Heating, Refrigerating and Air-Conditioning Engineers 

(ASHRAE) provides recommended indoor ventilation 

requirements for new homes in a standard known as ASHRAE 

62.2 (2010 is the most recent version). States and jurisdictions can 

adopt this standard by referencing it in their state or local building 

codes. Many utility weatherization programs require it and it is 

How Much Ventilation? 

In ASHRAE Standard 62.2, the 

the American Society of Heating, 

Refrigerating and Air-Conditioning 

Engineers recommends a continuous 

ventilation rate of 1 cubic foot per 

minute (cfm) per 100 ft2 of building 

area plus 7.5 cfm x (# bedrooms +1). An 

intermittent fan (an exhaust fan on a 

timer) can meet this requirement if the 

airflow rate is adjusted upward based 

on specific ventilation effectiveness 

requirements published in the standard.

August 2011 47

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ENERGY RENOVATIONS HVAC
Homes might use exhaust-only, supply-only, ERV/HRV, or some combination of all three types (Rudd 2011). 

48 August 2011

ENERGY RENOVATIONS HVAC
Kitchen

Range 

Hood

Bath 

Fan

Supply

Return

Air Handler

Supply

Supply Supply

Return

Filter

Upgraded 

Local Exhaust Fan 

in Bathroom or 

Common Area; 

also used for Whole 

House Ventilation

recommended by BPI and HERS raters. Most states that adopt 

the family of international building codes automatically adopt 

the International Mechanical Code, which includes less detailed 

requirements for mechanical ventilation. If you are remodeling an 

existing home, check with your building department to determine 

what ventilation requirements may apply. Even if not required 

by code, additional mechanical ventilation may be needed if you 

increase the air tightness of your home. Your energy performance 

contractor can advise you on how much ventilation is needed. 

4.1 Exhaust-Only Ventilation

For mechanical ventilation, the strategy most people are familiar 

with is exhaust-only, using exhaust fans located in bathrooms and 

over the kitchen range. Continuously operating an exhaust fan 

located in a bathroom or central area of the house provides low-cost 

ventilation that meets the requirement of ASHRAE 62.2, although 

this may not be the best option in humid climates where it can pull 

in humidity. High-quality, quiet, efficient fans that have lower and 

higher speeds for ventilation and exhaust are typically used for this 

application. Exhaust fans help to improve indoor air quality by 

removing air contaminants near their source, such as moisture from 

a shower. Exhaust fans, even ENERGY STAR-rated models, are a 

relatively inexpensive way to ventilate a home. It is important 

that each exhaust fan be ducted to the outside of the house 

and not into the attic. Another solution is to have several 

exhaust ducts that are connected and routed through a 

single, continuously operating, high-efficiency fan that is 

vented to the outside.

If exhaust fans are used and incoming air is not 

intentionally provided to the home, the home will 

depressurize (like sucking the air out of a straw), forcing 

outside air to be pulled in. Often it comes from somewhere 

undesirable, for example, from the crawlspace through 

cracks or holes in the subfloor or sill plates or from the 

garage through air leaks in adjoining walls and ceilings.

In a high-performance home, those air leaks have been 

sealed up, so a fresh air intake must be added to the home 

to supply fresh air. Failing to provide an outside air intake 

can cause the home to become negatively pressurized (i.e., 

depressurized). This can increase the risk of backdrafting 

any atmospheric-vented, combustion (fuel-burning) 

appliances or fireplaces that may be in the home. 

ENERGY STAR exhaust fans are available 

with sone ratings of 1.5 or less, indicating 

very quiet operation.

Exhaust fans provide simple, inexpensive 

ventilation but may depressurize the 

house, pulling air in from crawl spaces and 

through cracks in walls. (Rudd 2011).

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ENERGY RENOVATIONS HVAC
4.2 Supply-Only Ventilation 

Supply whole-house ventilation systems draw in fresh outside air 

from a known location (as opposed to through leaks in the building 

shell) and deliver it to the interior living space. The outside air can be 

brought in through a duct from a fresh air intake located for example 

in a porch ceiling or under a roof eave. The air can be brought 

through a filter on the air intake register and it should be conditioned 

by mixing it with recirculated indoor air before blowing it into living 

spaces (Rudd 2011).

Supply ventilation will tend to pressurize an interior space relative 

to the outdoors, causing inside air to be forced out through leaks in 

the building shell. In warm, humid climates, this strategy minimizes 

moisture entry into the building enclosure from outdoors. In cold 

climates, it may be advisable to balance the air intake with exhaust to 

minimize the risk of condensation inside walls (Rudd 2011).

Central fan integrated supply (CFIS) ventilation systems provide 

ventilation air through a duct that extends from outdoors to the 

return air side of a central heating and cooling system air handling 

unit (AHU). By using the existing central system air ducts, CFIS 

ventilation systems achieve full distribution of ventilation air. 

However, CFIS ventilation systems only provide ventilation air when 

the AHU fan is operating, therefore, an automatic timer must be 

used to ensure ventilation air is periodically supplied during periods 

of heating and cooling inactivity. A motorized outside air damper 

and associated control should also be added to limit outside air 

introduction to a maximum regardless of how long the fan operates. 

Continuous operation of the air handler fan is not recommended as 

it would consume too much electricity and is detrimental to humidity 

control in warm, humid climates (Rudd 2011).

Central fan integrated supply ventilation can be used with a central air 

handler equipped with an electronically commutated motor (ECM) 

rather than a permanent split capacitor (PSC) motor and some fan 

energy consumption savings may be possible (Rudd 2011). The key is 

that the ducts have been properly designed and installed according to 

manufacturers’ specifications to eliminate excessive airflow resistance. 

However, there are still concerns that at the high speed required to 

draw enough air in through the CFIS system the ECM is likely to have 

no savings relative to a PSC blower and at the lower air flows where 

the ECM performs better, the air flow through the exterior duct will 

not meet desired ventilation rates (Walker 2011). 

Because the operational time of the air handler fan is increased with 

central fan integrated ventilation, the importance of sealing and 

Supply-only ventilation brings in fresh 

outside air through a dedicated duct 

(Rudd 2011).

Air Handler

Outside 

Air

Supply Supply

Supply

Kitchen

Range 

Hood

Bath 

Fan

Return

Filter Manual

Damper

(controls

flow rate)

Motorized 

Damper

(controls

open time)

Supply

50 August 2011

ENERGY RENOVATIONS HVAC
Kitchen

Range 

Hood

Bath 

Exhaust

HRV/ERV

Hall

Supply

Outside Air

Common

Area

Supply

Bath 

Exhaust

Inside Air

insulating the ducts is increased. Of course, for every central space 

conditioning system, the best practice is always to locate the entire air 

distribution system inside conditioned space (Rudd 2011).

For homes that don't have a central heating and cooling system, a fan, 

like an exhaust fan, can be used to draw in outside air. This outside air 

should be mixed with indoor air to temper it before it is delivered into 

the home (Rudd 2011).

4.3 Balanced Systems

Balanced systems intentionally provide both supply and exhaust. 

The best means for providing this balanced ventilation is with a 

heat recovery ventilator (HRV) or an energy recovery ventilator 

(ERV). Both provide a controlled way of ventilating a home while 

minimizing energy loss because they incorporate a heat exchanger 

that uses the heat or cooling from the outgoing exhaust air to warm 

or cool the fresh incoming air. The incoming and outgoing air 

volumes are balanced and air is evenly distributed throughout the 

house. These ventilators are whole-house systems; they can share 

a central furnace air handler and duct system or have their own 

duct system. The main difference between an HRV and an ERV 

is the way the heat exchanger works. With an ERV (also called an 

enthalpy-recovery ventilator), the heat exchanger transfers water 

vapor along with heat energy, while an HRV only transfers heat. See 

the manufacturers' specifications for determining which model is best 

in which climate and install it according to their directions for best 

performance, especially in regard to ERVs in humid climates. Most 

ERVs can recover about 70% to 80% of the sensible energy in the 

exiting air (Rudd 2011). 

4.4 “Semi-Balanced” System

Balanced whole-house ventilation systems both exhaust and supply 

in roughly equal amounts. Inside air is exhausted to the outdoors 

and outside air is supplied indoors. Balanced ventilation, by 

definition, should not affect the pressure of the interior space relative 

to outdoors. HRVs and ERVs are balanced systems. A balanced 

system can also be made up of any combination of the exhaust and 

supply ventilation systems described above (Rudd 2011). In reality 

the balance may never be perfect due to fluctuations in wind and 

stack pressures. Balanced ventilation can be used effectively in any 

climate. Rudd 2011 shows several examples of configurations of 

balanced systems.

Semi-balanced ventilation systems provide 

fresh air and exhaust stale air but flow rates 

may not be balanced (Rudd 2011).

Outside 

Air

Supply Supply

Manual

Damper

(controls

flow rate)

Motorized 

Damper

(controls

open time)

Kitchen

Range 

Hood

Bath 

Exhaust Return

Filter

Bath 

Exhaust

Supply

Return

Supply

AHU

Heat and energy recovery ventilators bring 

in fresh air, exhaust stale air, and save 

energy by transferring heat to incoming air 

through a heat exchanger (Rudd 2011).

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ENERGY RENOVATIONS HVAC
Table 4.1. Summary of whole-house ventilation system types and cost and performance 

trade-offs (adapted from Rudd, A. 2011. “Local Exhaust and Whole House Ventilation Strategies,” 

prepared by BSC for DOE Building America)

Balanced Systems Exhaust Systems Supply Systems 

ERVs/HRVs and semi-balanced exhaust/

supply

• Exhaust fan and fresh air supply fan 

running simultaneously. 

• Can be integrated with heat/cool system 

ducts and air handler. 

• Use timers or other controls to empower 

continuous and intermittent use.

• Install heat recovery ventilator or energy 

recovery ventilator with independent 

system of smaller sized ducts to 

supply filtered outdoor air to each 

room or zone and return stale air from 

each room or zone passing thru heat 

exchanger enroute to exhaust vent 

to temper incoming air. ERVs transfer 

some moisture as well.

• Use continuous operation or use 

timers or other controls to empower 

intermittent use.

• Use a fresh air duct into central air 

handler return duct, or use a separate 

supply fan with recirculation air for 

tempering. 

• Use a fan timer and damper control. 

• Combined with low airflow resistance, 

ECM air handlers help save energy.

Advantages: 

• Most effective regardless of house 

airtightness. 

• Applicable in all climate zones. 

• Known source of ventilation air. 

• Less likely to affect combustion 

appliance venting.

• HRV or ERV technology can recover up 

to 70% of heat. 

• Have opportunity to filter and temper 

fresh air.

Advantages: 

• Simple and inexpensive. 

• Good for removal of pollutants at their 

source. 

• Good, quiet local exhaust can double for 

whole-house ventilation. 

• Negative pressure can help keep walls 

drier in cold climates.

Advantages: 

• Simple, inexpensive, uses existing 

central duct system. 

• Known source of ventilation air. 

• Ensures good fresh air distribution. 

• Gives opportunity to filter and condition 

fresh air. 

• Positive pressure minimizes combustion 

spillage potential, and can help keep 

walls drier in warm, humid climates.

• Tempers fresh air and filters it if filter is 

located at the air handler after the air 

inlet not at return grilles.

Design/Installation Issues: 

• Requires interlock with central air. 

handler fan if integrated with central 

ducts. 

• ERVs/HRVs more expensive first cost. 

• ERVs/HRVs require pre-planning for 

unit, vents, and duct locations.

Design/Installation Issues: 

• Unknown source and entry path of 

outdoor air. 

• Test to see if make-up air is needed to 

avoid combustion spillage and soil gas 

entry.

• No opportunity to filter, temper, or 

condition incoming air. 

• May lack fresh air distribution.

Design/Installation Issues: 

• Need proper duct design and 

installation to ensure adequate air flow. 

• Need proper register grille design to 

avoid uncomfortable drafts.

• Still need bathroom local exhaust.

• May need to operate blower 

continuously to get enough air flow.

52 August 2011

ENERGY RENOVATIONS HVAC
The U.S. Department of Energy Office of Renewable Energy and 

Energy Efficiency (DOE-EERE) and the U.S. Environmental 

Protection Agency are committed to a whole-house approach to 

energy upgrading a home to ensure homeowner health and safety 

as well as cost-effective energy savings. This approach is based 

on an understanding that every system in the home interacts 

with the other systems in the home. Thus, changes to the home's 

heating, ventilating, and cooling equipment can have health and 

safety consequences that must be taken into account. A home 

energy performance assessment, conducted by trained contractors, 

following recognized guidelines such as DOE’s Workforce Guidelines 

for Home Energy Upgrades, will take into account these interactions 

and help homeowners identify and implement safe, effective energy 

improvements. 

Homeowners should have a home energy performance assessment 

done when adding or replacing HVAC equipment, when they want 

to improve their home's efficiency by air sealing or adding new 

insulation, or when they are planning a major remodelling project.

5.1 Certified Energy Contractors

A Building America-approved home energy assessment is conducted 

by a contractor who is trained and certified in building science 

principles and follows a prescribed approach to ensure the safest and 

most efficient ways to improve your home’s energy efficiency. 

There are two nationally recognized energy certifications for home 

performance energy contractors: the Building Performance Institute 

(BPI) Building Analyst certification and the Residential Energy 

Services Network (RESNET) HERS Rater certification. Historically, 

Building Performance Institute -The BPI 

is a nonprofit organization that accredits 

auditors, contractors, and other building 

professionals. Auditors or building analysts 

specialize in evaluating building systems 

and potential energy savings in homes. 

The certified BPI Building Analyst energy 

auditor has passed both written and field 

exams, and must recertify every three 

years. Contractors learn about building 

systems and are trained to perform energy 

efficiency assessments and conduct 

combustion safety testing. For more 

information see www.BPI.org

A certified Residential Energy Services 

Network (RESNET) energy auditor is called 

a HERS rater. HERS raters are certified to 

provide homes with a HERS (the Home 

Energy Rating System) score, which 

provides a miles-per-gallon type rating of 

expected energy consumption that makes 

it easy to compare the energy performance 

of one home to another. More information 

about HERS can be found at www.resnet.us.

5.0 The Home Performance 

Energy Assessment

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ENERGY RENOVATIONS HVAC
BPI certification has focused on understanding the building science 

of retrofitting existing homes and RESNET has focused on building 

science in new home construction. Also, states have adapted BPI 

and RESNET standards in state-specific training programs offered 

through weatherization programs and Home Performance with 

ENERGY STAR, a national program from EPA and DOE that 

promotes a comprehensive, whole-house approach to energyefficiency improvements.

5.2 The Energy Assessment 

Process

Details of a home energy assessment will vary by program, but here 

is what you can typically expect.

5.2.1 Step 1. The Energy Performance 

Assessment 

First, the energy contractor will evaluate the homeowner’s energy 

upgrade needs, comfort issues, past home energy performance, 

home health and safety, and cost considerations. Here is what your 

assessment should include:

• SIZING THINGS UP – The contractor will interview you to 

understand your concerns about any comfort, heating, cooling, 

or safety issues related to your home. The contractor will ask 

for printouts of the last 12 months of utility bills, which you can 

access by contacting your utility companies. The utility data will 

show if your house is using too much energy for heating or cooling 

and areas to focus on for improvement. The contractor will take 

measurements of your home’s total square footage, window 

area, and door area, and document specific features of the living 

space, such as if a basement is heated or cooled through furnace 

ducts. While taking these measurements, the contractor will also 

visually check for moisture problems outside and inside the home, 

including site drainage issues, gutter problems, and any evidence of 

water staining, dry rot, or mold.

• TESTING – With this preliminary information collected, the 

energy contractor begins conducting safety tests. These include 

checking all natural gas lines and gas appliances for gas leaks, 

performing a worst-case depressurization test and worst-case 

spillage test for combustion (fuel-burning) appliances that are 

naturally drafting (lack an enclosed flue pipe), and checking 

carbon monoxide levels around combustion furnaces and 

appliances. Exhaust fan operation is checked. Insulation levels 

pink = insulation 

blue = air barrier

As part of an energy performance 

assessment, your certified energy 

contractor will do a thorough visual 

inspection of your home and conduct 

combustion safety and air leakage testing.

The home’s building envelope 

contains the insulation in the 

attic, walls, and floor. This 

insulation should be in contact 

with a continuous air barrier 

that could include the taped 

drywall of the walls and ceiling 

and caulked subfloor plus 

weather-stripped doors and 

windows. Any holes in this air 

barrier (for wiring, plumbing, 

flue pipes, etc.) should be 

caulked to keep air from 

leaking in or out.

54 August 2011

ENERGY RENOVATIONS HVAC
in walls, attics, and basements are visually checked. Ducts are 

visually inspected. Furnace filters are checked. After all safety 

tests reveal that the whole house operates safely, only then will 

the contractor conduct tests to determine energy performance. 

These tests include a blower door test to measure whole-house 

air leakage and a duct blaster test to measure duct leakage. Tools 

like a pressure pan, infrared camera, or smoke stick also might be 

used to identify air leaks.

• SAFETY FIRST – Visual inspections and health and safety tests 

can identify problems that need immediate attention, such as a 

hole in a roof or excessive mold in a wall structure. Addressing 

these problems is a priority, and the energy upgrade process will 

continue after such issues are resolved.

• COST-BENEFIT ANALYSIS AND ESTIMATES – The contractor 

will estimate the costs of installing specific energy-improvement 

measures and use a computer program to estimate the expected 

energy savings. The cost of the measures divided by the annual 

savings will tell you the “simple payback” or how many years the 

measures will take to pay for themselves. Often investments in 

energy efficiency provide a better return than stocks, bonds, or 

savings accounts, while improving comfort.

5.2.2 Step 2. Making Energy-Efficiency 

Upgrades

Within a week or so, the contractor will review the test results and 

provide you with a detailed proposal, including a prioritized list of 

energy-efficiency measures, packaged options, and price estimates. 

Together you agree on an energy-upgrade approach, costs, and 

timelines. Sometimes the certified analyst is an HVAC contractor 

who can perform the work. Other times, the energy contractor brings 

in qualified contractors and subcontractors as needed. An energy 

contractor understands state and local building codes and will work 

with code officials when necessary to ensure that the improvements 

meet building code requirements.

5.2.3 Step 3. Testing Out

After the energy upgrades are completed, your contractor will 

conduct another round of testing to make sure the renovations have 

improved the home’s performance and that safety standards have 

been met. This “testing out” step usually includes visual inspections, 

combustion safety (if open-combustion equipment is in the home), 

and duct blaster and blower door tests. Homeowners should receive 

a report summarizing the work completed, test results, and estimated 

energy savings.

After energy-efficiency improvements are 

done, the house is tested out with a blower 

door, duct leakage, and other tests to make 

sure the home’s energy performance has 

been improved and that safety standards 

are met.

August 2011 55

55

ENERGY RENOVATIONS HVAC
References

ACCA. 1995. Manual S: Residential Heating and Cooling Equipment Selection, Air Conditioning Contractors of America, Arlington, VA. 

www.acca.org

ACCA. 2005. Manual J: Residential Load Calculation, Eighth Edition. Air Conditioning Contractors of America, Arlington, VA. www.acca.

org

ACCA. 2009. Manual D: Residential Duct Systems. Air Conditioning Contractors of America, Arlington, VA. www.acca.org

ACCA. 2010a. ANSI/ACCA Standard #4 Maintenance of Residential HVAC Systems, Air Conditioning Contractors of America, Arlington, 

Virginia, https://www.acca.org/industry/quality/quality-maintenance

ACCA. 2010b. ANSI/ACCA Standard #5 HVAC Quality installation Specification, Air Conditioning Contractors of America, Arlington, 

Virginia, https://www.acca.org/industry/quality/quality-installation

ACCA. 2010c. ANSI/ACCA Standard #6 Restoring the Cleanliness of HVAC Systems, Air Conditioning Contractors of America, Arlington, 

Virginia, https://www.acca.org/industry/quality/quality-restoration

ACCA. 2010d. ANSI/ACCA Standard #9 Quality Installation Verification. Air Conditioning Contractors of America, Arlington, Virginia, 

www.acca.org https://www.acca.org/industry/quality/quality-verification

ACCA. 2011a. Residential Quality HVAC Installation, Air Conditioning Contractors of America, accessed 6-21-11, www.acca.org/ 

Files/?id=186

ACCA. 2011b. Verifying ACCA Manual J Procedures. Air Conditioning Contractors of America, accessed 6-20-2011, https://www.acca.org/

Files/?id=68

ACCA. 2011c. Verifying ACCA Manual S Procedures. Air Conditioning Contractors of America, accessed 6-20-2011, https://www.acca.org/

Files/?id=67

ACEEE. 2011. “Appliance Standards Awareness Project,” American Council for an Energy-Efficient Economy, http://www.standardsasap.

org/

AHRI. 2003. Unitary Air Conditioning and Air-Source Heat Pump Equipment. Standard 210/240, Air-Conditioning & Refrigeration 

Institute. Arlington, Virginia, http://www.ahrinet.org/App_Content/ahri/files/standards%20pdfs/Superseded%20Standards/AHRI%20

(ARI)%20Standard%20210.240-2003.pdf

ANSI. 2011. “Resources: Conformity Assessment Bodies in the U.S.,” American National Standards Institute, www.standardsportal.org/

usa_en/resources/cab.aspx

APS. 2009. “Shade Treatments and Window Treatments.” Arizona Public Service Company, MM-5K-0699-AS, http://www.aps.com/

aps_services/residential/waystosave/ResWaystoSave_9.html

ASHRAE. 2007. Standard 52.2-2007, “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle 

Size,” American Society of Heating, Refrigerating and Air Conditioning Engineers, www.ashrae.org

Beal, D. J. McIlvaine, K. Fonorow, and E. Martin. 2011. Summary of Interior Ducts in New Construction, Including an Efficient, Affordable 

Method to Install Fur-Down Interior Ducts, prepared by BA-PIRC/Florida Solar Energy Center for the U.S. Department of Energy 

Building America program, www.buildingamerica.gov

CEC. 2009. “Procedures for HVAC System Design and Installation,” California Energy Commission. www.energy.ca.gov/efficiency/

qualityhomes/procedures.html

California Energy Commission. 2011. “Geothermal Ground Source Heat Pumps.” http://www.consumerenergycenter.org/home/heating_

cooling/geothermal.html

ConsumerSearch, Inc. 2008. “Central Air Conditioners: Reviews.” The New York Times Company. http://www.consumersearch.com/

central-air-conditioners

Cummings, J., C. Withers, E. Martin, and N. Moyer. 2011. Managing the Drivers of Air Flow and Water Vapor Transport in Existing Single 

Family Homes, prepared by BA-PIRC/Florida Solar Energy Center for the U.S. Department of Energy Building America program, www.

buildingamerica.gov

DOE. 2007. Building America Best Practices Series, Volume 6: High-Performance Home Technologies: Solar Thermal & Photovoltaic 

Systems. NREL/TP-550-41085; PNNL-16362, Prepared by Pacific Northwest National Laboratory for the U.S. Department of Energy, 

Richland, WA. www.pnl.gov/main/publications/external/technical_reports/PNNL-16362.pdf

DOE. 2009. “Table 2.1.6 2010 Residential Energy End-Use Splits, by Fuel Type.” U.S. Department of Energy Building Energy Data Book. 

http://buildingsdatabook.eren.doe.gov/TableView.aspx?table=2.1.6

DOE. 2010. “Energy Savers: Space Heating and Cooling.” U.S. Department of Energy. http://www.energysavers.gov/your_home/space_

heating_cooling/

DOE. 2011. Building America Best Practices Series Volume 12: Builders Challenge Guide to 40% Whole-House Energy Savings in the Cold 

and Very Cold Climates, PNNL-20139, Prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy, www.

buildingamerica.gov

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ENERGY RENOVATIONS HVAC
Eastment, M., E. Hancock, and C. Kutscher. 2005. Projected Costs and Benefits of New Residential Evaporative Cooling Systems, Golden, CO: 

National Renewable Energy Laboratory. www.nrel.gov/docs/fy07osti/39342.pdf

EIA. 2005. “Residential Energy Consumption Survey: Preliminary Housing Characteristics Tables,” U.S. Energy Information Administration, 

http://www.eia.doe.gov/emeu/recs/

EIA. 2010. “Geothermal Heat Pump,” U.S. Energy Information Administration. http://www.eia.gov/cneaf/solar.renewables/page/heatpumps/

heatpumps.html

EIA. 2008. “Average Expenditures for Air-Conditioning by Equipment Type, 2005,” U.S. Energy Information Administration. http://www.eia.

doe.gov/emeu/recs/recs2005/c&e/airconditioning/excel/tableac7.xls

Farzad, M. and D.L. O’Neal. 1998. An Evaluation of Improper Refrigerant Charge on the Performance of a Split System Air Conditioner with 

Capillary Tube Expansion, Prepared for the Energy Systems Laboratory Research Consortium, Texas A&M University. ESLTR-88/07-01. 

http://repository.tamu.edu/bitstream/handle/1969.1/2041/ESL-TR-88-07-01.pdf?sequence=1

Henkenius, Merle. 1998. “Geothermal Heating,” Popular Mechanics, Oct 1, 1998, http://www.popularmechanics.com/home/improvement/

energy-efficient/1274631

IECC. 2009. International Energy Conservation Code, International Code Council (ICC), Washington, D.C. www.iccsafe.org/Store/Pages

Karr, M. 2011. “Ground-Source Variable Refrigerant Flow Heat Pumps,” Washington State University Extension Energy Program, www.energy.

wsu.edu/Documents/EEFactsheet-GSHP-Feb2011.pdf

Krigger, John and Chris Dorsi. 2009. Residential Energy: Cost Savings and Comfort for Existing Buildings, 5th Edition, Saturn Resource 

Management, http://srmi.biz/Bookstore.Professionals.Residential_Energy.htm

LBNL. 2011. “Energy Efficiency Standards,” Lawrence Berkeley National Laboratory, accessed 2011. http://ees.ead.lbl.gov/taxonomy/term/1

McPherson, G.E., D.J. Nowak, and R.A. Rowntree (eds). 1994. Chicago’s Urban Forest Ecosystem: Results of the Chicago Urban Forest Climate 

Project. U.S. Department of Agriculture, Forest Service, Northeastern Research Station.

McWilliams, J.A., I.S. Walker 2005. Renovating Residential HVAC Systems, Lawrence Berkeley National Laboratory. LBNL 57406. http://epb.lbl.

gov/publications/lbnl-57406.pdf

Northwest Energy Efficiency Alliance. 2009. “Ductless Heat Pump Project,” NEEA, http://www.nwductless.com/

NRCan. 2009. “Personal: Residential Air-Source Heat Pumps,” Natural Resources Canada, http://oee.nrcan.gc.ca/publications/infosource/pub/

home/heating-heat-pump/asheatpumps.cfm

Parker, D., J. Sherwin. 2008. Experimental Evaluation of the NightCool Nocturnal Radiation Cooling Concept: Annual Performance Assessment 

in Scale Test Buildings, Florida Solar Energy Center, http://securedb.fsec.ucf.edu/pub/pub_show_detail?v_pub_id=4389

Rudd, Armin, Joseph Lstiburek, and Kohta Ueno. 2005. Residential Dehumidification Systems Research for Hot-Humid Climates, Building 

Science Corporation Research Report 0505, http://www.buildingscience.com/documents/reports/rr-0505-residentialdehumidificationsyste

ms-research-for-hot-humid-climates

Rudd, Armin. 2011. Local Exhaust and Whole House Ventilation Strategies, Prepared by Building Science Corporation for the U.S. Department 

of Energy, www.buildingamerica.gov 

Russell, Marion, Max Sherman, and Armin Rudd, 2005. Review of Residential Ventilation Technologies. LBNL Report 57730, Ernest Orlando 

Lawrence Berkeley National Laboratory. http://www.buildingscience.com/documents/guides-and-manuals/gm-reviewresidentialventilationtechnologies/at_download/file

Sherman, M.H., I.S. Walker, and D.J. Dicerkhoff. 2000. “Stopping Duct Quacks: Longevity of Residential Duct Sealants,” in Proceedings of the 

2000 ACEEE Summer Study on Energy Efficiency in Buildings, prepared by Lawrence Berkeley National Laboratory. www.osti.gov/bridge/

product.biblio.jsp?query_id=1&page=3&osti_id=776574

Sherwin, J., C. Colon, D. Parker, and E. Martin. 2010. “Performance of Four Near Zero Energy Homes: Lessons Learned,” In Proceedings of the 

ASHRAE Thermal Performance of the Exterior Envelopes of Whole Buildings XI International Conference, December 5-9, 2010, in Clearwater 

Beach, FL, FSEC-PF-452-10, Florida Solar Energy Center, www.baihp.org/pubs/pdf/4zehs_B11.pdf

Smith, B.R. and J. Arco. 1996. "Do You Dig Ground Source Heat Pumps?" Home Energy Magazine, www.homeenergy.org/archive/hem. dis.

anl.../961112.html

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Walker, L. and S. Newman. 2009. Landscaping for Energy Conservation. No 7.225, www.treesearch.fs.fed.us/pubs/4285

August 2011 57

57

ENERGY RENOVATIONS HVAC
Definitions

AIR HANDLER: Air handlers blow air through the ductwork for heating, cooling, or ventilation purposes.

ANNUAL FUEL UTILIZATION EFFICIENCY (AFUE): The AFUE measures the amount of fuel converted to 

space heat in proportion to the amount of fuel entering the boiler or furnace. This is commonly expressed as a 

percentage. Test procedures have been developed by the Department of Energy to test AFUE. 

BRITISH THERMAL UNIT (BTU): A Btu is a unit of energy that is commonly used when describing heating 

systems.

CONDITIONED SPACE: Conditioned space includes the sections of your house that are intentionally heated 

and/or cooled. Conditioned space is surrounded by a continuous thermal envelope, which includes an air barrier 

and thermal barrier. Attics, for example, are unconditioned space if they are vented and have insulation on the 

attic floor. If you have an unvented attic with insulation along the attic slopes, it is part of the conditioned space. 

COEFFICIENT OF PERFORMANCE (COP): COP is a measure of efficiency in the heating mode that 

represents the ratio of total heating capacity to electrical energy input. For example, if a heating system has a 

COP of 3, it will deliver 3 units of energy for every one unit of electricity consumed. 

ENERGY EFFICIENCY RATIO (EER): EER is a measure of the instantaneous energy efficiency of cooling 

equipment. EER is the steady-state rate of heat energy removal (e.g., cooling capacity) by the equipment in 

Btu/h divided by the steady-state rate of energy input to the equipment in watts. This ratio is expressed in Btu/h 

per watt (Btu/h/watt). EER is based on tests performed in accordance with AHRI 210/240 (AHRI 2003). 

HEATING SEASONAL PERFORMANCE FACTOR (HSPF): The HSPF is a measure of a heat pump’s 

energy efficiency over one heating season. It represents the total heating output of a heat pump (including 

supplementary electric heat) during the normal heating season (in Btu) as compared to the total electricity 

consumed (in watt-hours) during the same period. HSPF is based on tests performed in accordance with AHRI 

210/240 (AHRI 2003). 

INTERNATIONAL ENERGY CONSERVATION CODE (IECC): The IECC 2009 was published in January 

2009. The IECC 2012 will be published in June 2011.

SEASONAL ENERGY EFFICIENCY RATIO (SEER): SEER is a measure of equipment energy efficiency over 

the cooling season. It represents the total cooling of a central air conditioner or heat pump (in Btu) during the 

normal cooling season as compared to the total electric energy input (in watt-hours) consumed during the same 

period. SEER is based on tests performed in accordance with AHRI 210/240 (AHRI 2003). 

58 August 2011

ENERGY RENOVATIONS HVAC
Advanced Residential Integrated 

Energy Solutions (ARIES) 

Lead: The Levy Partnership, Inc. 

Members: CDH Energy, Southern 

Energy Management, Syracuse 

University Center of Excellence, 

NTA, Inc., Corporation for 

Enterprise Development, Ford 

Foundation, Fannie Mae, Habitat 

for Humanity International, 

Manufactured Housing Institute, 

NeighborWorks America, New 

York State Energy Research & 

Development Authority, Systems 

Building Research Alliance.

Alliance for Residential 

Building Innovation 

(ARBI)

Lead: Davis Energy 

Group

Members: Rocky Mountain 

Institute, the UC Davis Western 

Cooling Efficiency and Lighting 

Technology Centers, Polaris, 

Heschong Mahone Group, Recurve, 

Green Home Solutions, BevilacquaKnight, Renewable Funding. 

Building America Retrofit Alliance 

(BARA)

Lead: Building Media, Inc,

a subsidiary of E. I. du Pont de Nemours and Co

Members: New Jersey Institute of 

Technology Center for Building 

Knowledge, Steve Easley and 

Associates, and Confluence 

Communications. 

Building America 

Partnership 

for Improved 

Residential 

Construction 

(BA-PIRC)

Lead: Florida Solar Energy Center 

(FSEC)

Members: Newport Partners, 

Washington State University, 

Northwest Energy Works, 

Residential Energy Services 

Network, Gas Technology Institute, 

WellHome, Florida Home Energy 

and Resources Organization, CalcsPlus and TexEnergy Solutions.

Building America Teams

Building Energy 

Efficient Homes for 

America (BEEHA)

Leads: University of 

Nebraska-Lincoln, 

Lincoln, NE, and the University of 

Florida, Gainesville, FL

Members: HearthStone Homes, 

Rezac Construction, City of 

Omaha, Home Builders Association 

of Lincoln, Lincoln Remodelers 

Council, HolyName Housing 

Cooperation, Excite Builders, City 

of Lincoln, Barry Rutenberg and 

Associates, G.W. Robinson Homes, 

Tommy Williams, Stephan O. Nellis, 

Omaha Public Power District and 

Johnson Controls. 

Building Industry Research 

Alliance (BIRA)

Lead: Consol 

Members: Washington State 

University, Arizona State 

University, UC Davis, University 

of Utah, General Electric, PVT, 

MASCO, Ennovationz, Tendril, 

Sacramento Municipal Utilities 

District, San Diego Gas & Electric, 

Arizona Public Service, Salt River 

Project, Bank of America.

Building Science Corporation 

(BSC)

Lead: BSC 

Members: Affordable Comfort, 

ARES Consulting, Camroden 

Associates, Community and 

Economic Development 

Association of Cook County, 

DEAP Energy Group, Greencoast 

Enterprises, Transformations, Inc., 

National Grid, and Michael Blasnick 

& Associates. 

Consortium for 

Advanced Residential 

Buildings (CARB)

Lead: Steven Winter Associates, 

Inc., 

Members: MaGrann Associates, 

Green Builder Media, Alliance to 

Save Energy's Building Codes 

Assistance Project, Pratt Center 

for Community Development, 

Masco Home Services/WellHome, 

Fraunhofer Center for Sustainable 

Energy Systems, Jay Hall & 

Associates, Inc., Johnson Research 

and Polaris Consulting Engineers.

Fraunhofer Center for Sustainable 

Energy Systems (CSE)

Lead: Fraunhofer Center for 

Sustainable Energy Systems

Members: Owens Corning, 

Fraunhofer Institute for Solar 

Energy Systems (ISE), Fraunhofer 

Institute for Building Physics 

(IBP), Architect Research Partners, 

Next Phase Studios Architects, 

Barley & Pfeiffer Architects, 

WBRC, Conservation Services 

Group, Byggmeister, Cambridge 

Design and Development, and 

Massachusetts Institute of 

Technology. 

Habitat Cost Effective Energy 

Retrofit Program

Lead: Dow Chemical Company

Members: Michigan State 

University, Ferris State University, 

and Habitat for Humanity, with 

technical contributions from Duke 

Energy, DTE, and Exelon. 

IBACOS

Lead: IBACOS

Members: building scientists and 

trainersproduction homebuilders, 

whole house retrofit companies. 

NAHB Research 

Center Industry 

Partnership for 

High Performing 

Homes (NAHBRC 

Partnership)

Lead: NAHB Research Center

Members: Southface Energy 

Institute, ARES Consulting, Jeannie 

Leggett Sikora, USDA Forest 

Products Laboratory, Business 

Excellence Consulting, Brick by 

Brick, Residential Building Industry 

Consulting Services, Utilivate 

Technologies. 

National Energy Leadership Corps 

(N.E.L.C.)

Lead: Pennsylvania State University

Members: SmartDwell, Sequentric 

Energy Systems, Envinity, 

ONTILITY, Solar Strategies, 

Eaton Corporation, Pittsburgh 

Green Innovators, Partnership for 

Achieving Construction Excellence 

(PACE), Conservation Consultants, 

East Liberty Development, and the 

Green Building Alliance. 

NorthernSTAR Building America 

Partnership

Lead: University of Minnesota

Members: Center for Energy and 

Environment, Energy Center of 

Wisconsin, Building Knowledge, 

Building Green, Conservation 

Technologies, Hunt Utilities 

Group, Verified Green, Wisconsin 

Energy Conservation Corporation, 

McGregor Pearce, Minnesota 

Pollution Control Agency, the 

University of Wisconsin, and 

Wagner Zaun Architecture. 

Partnership 

for Advanced 

Residential 

Retrofit (PARR)

Lead: Gas 

Technology 

Institute 

Members: CNT Energy, the 

Midwest Energy Efficiency Alliance, 

the Building Research Council 

at the University of Illinois, and 

Future Energy Enterprises.

The National Energy Leadership Corps

Alliance for

Residential

Building

Innovation

The Partnership

for Advanced

Residential Retrofit

August 2011 59

59

ENERGY RENOVATIONS HVAC
EERE Information Center 

1-877-EERE-INFO (1-877-337-3463) 

www.eere.energy.gov/informationcenter

August 2011 - PNNL-20421

For information on Building America 

visit www.buildingamerica.gov. 

The website contains expanded 

case studies, technical reports, and 

best practices guides.

Building America Program

Building America Program • 1-877-EERE-INFO (1-877-337-3463) 

Office of Building Technologies, EE-2J • U.S. Department of Energy • 

1000 Independence Avenue, S.W. • Washington, D.C. 20585-0121 • 

www.buildingamerica.gov

National Renewable Energy Laboratory

www.nrel.gov

Oak Ridge National Laboratory

www.ornl.gov

Pacific Northwest National Laboratory

www.pnnl.gov

Produced for the U.S. Department of Energy (DOE) by Pacific Northwest National Laboratory, 

Under Contract DE-AC05-76RLO 1830.

Research and 

Development of Buildings

Our nation’s buildings consume 

more energy than any other sector 

of the U.S. economy, including 

transportation and industry. 

Fortunately, the opportunities to 

reduce building energy use—and 

the associated environmental 

impacts—are significant.

DOE’s Building Technologies 

Program works to improve the 

energy efficiency of our nation’s 

buildings through innovative new 

technologies and better building 

practices. The program focuses 

on two key areas:

• Emerging Technologies 

Research and development of 

the next generation of energyefficient components, materials, 

and equipment

• Technology Integration of new 

technologies with innovative 

building methods to optimize 

building performance and savings

Visit our Websites at:

www.buildingamerica.gov

www.energystar.gov

R