Evaluating Ventilation Systems 

for Existing Homes

Robb Aldrich and Lois Arena

Consortium for Advanced Residential Buildings

February 2013
ii

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iii

Evaluating Ventilation Systems for Existing Homes

Prepared for:

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway

Golden, CO 80401

NREL Contract No. DE-AC36-08GO28308

Prepared by:

Robb Aldrich and Lois Arena

Steven Winter Associates, Inc.

of the

Consortium for Advanced Residential Buildings (CARB)

61 Washington Street

Norwalk, CT 06854

NREL Technical Monitor: Cheryn Metzger

Prepared under Subcontract No. KNDJ-0-40342-00

February 2013
iv

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v

Contents

List of Figures ............................................................................................................................................ vi

List of Tables .............................................................................................................................................. vi

Definitions and Abbreviations ................................................................................................................. vii

Executive Summary................................................................................................................................. viii

1 Introduction........................................................................................................................................... 1

2 Background: Key Ventilation Considerations................................................................................... 3

2.1 Ventilation Levels and Needs..............................................................................................3

2.2 Installation and Integration With Existing Systems.............................................................4

2.3 Distribution and Mixing of Outdoor Air..............................................................................5

2.4 Source of Outdoor Air .........................................................................................................8

2.5 Energy Implications.............................................................................................................9

2.6 Operation and Maintenance .................................................................................................9

3 What Systems Are Being Installed? ................................................................................................. 11

3.1 Weatherization and Similar Programs...............................................................................11

3.2 Deep Energy Retrofits and Similar Projects......................................................................12

3.3 Midrange Energy Improvement Efforts.............................................................................13

4 Systems Evaluated and Cost Analysis ............................................................................................ 14

4.1 Exhaust Ventilation............................................................................................................14

4.2 Central Fan Integrated Supply ...........................................................................................15

4.3 Ducted Energy or Heat Recovery Ventilator.....................................................................15

4.4 Local Energy Recovery Ventilator ....................................................................................17

4.5 Cost Comparisons..............................................................................................................18

5 Conclusions ........................................................................................................................................ 19

6 Discussion........................................................................................................................................... 20

6.1 Other Projects and Climates...............................................................................................20

6.2 Gaps and Additional Systems............................................................................................21

6.2.1 Larger Capacity Local Energy Recovery Ventilator .............................................21

6.2.2 Energy Recovery Ventilator With Limited Ducting..............................................21

6.2.3 Mixing....................................................................................................................21

References................................................................................................................................................. 23

Bibliography .............................................................................................................................................. 26
vi

List of Figures

Figure 1. One of the homes in Las Vegas, Nevada tested with several ventilation systems.............. 1

Figure 2. Convoluted or extremely long duct runs can dramatically reduce exhaust fan flow rates.3

Figure 3. Summary of RAoA tests from (CARB 2010). In both test cases, all interior doors are 

closed with exhaust ventilation operating continuously. In Case 1, the mixing fan is running. . 7

Figure 4. With significant space and ducting requirements, fully ducted ERV or HRV systems are 

often more practical in major renovation projects.......................................................................... 13

Figure 5. New bathroom exhaust fan installed in a CCCRD home ...................................................... 14

Figure 6. Simple schematic of CFIS ventilation system ....................................................................... 15

Figure 7. Images of Panasonic’s WhisperComfort ERV. At right, installed (with cover removed) in 

the ceiling of a CCCRD home............................................................................................................ 17

Unless otherwise noted, all figures were created by CARB.

List of Tables

Table 1. Overview of Whole-Building Ventilation Systems Evaluated and Considered in CCCRD 

Homes.................................................................................................................................................. 18

Table 2. Cost Comparisons for Several Ventilation Systems Considered in an Example Las Vegas 

Home.................................................................................................................................................... 19

Unless otherwise noted, all tables were created by CARB.
vii

Definitions and Abbreviations

ACH Air changes per hour

ACH50 Air changes per hour when building is depressurized to 50 

Pascals

AHU Air handling unit

ASHRAE American Society of Heating, Refrigerating and AirConditioning Engineers

BAS Building airflow standard

BPI Building Performance Institute

CARB Consortium for Advanced Residential Buildings

CCCRD Clark County Community Resources Division

CFIS Central fan-integrated supply (ventilation)

CFM Cubic feet per minute

DER Deep energy retrofit (or reduction)

ECM Electronically commutated motor

ERV Energy recovery ventilator (for sensible and latent heat)

HERS Home Energy Rating System

HRV Heat recovery ventilator (recovers sensible heat only)

HVAC Heating, ventilation, and air conditioning

HVI Home Ventilating Institute

IEQ Indoor environmental quality

LEED Leadership in Energy and Environmental Design

NREL National Renewable Energy Laboratory

OA Outdoor air

RAoA Reciprocal age of air [hr-1]

w.g. Water gauge
viii

Executive Summary

In an effort to improve housing options near Las Vegas, Nevada, the Clark County Community 

Resources Division (CCCRD) performs substantial renovations to foreclosed homes. After 

dramatic energy, aesthetic, and health and safety improvements are made, homes are rented or 

sold to qualified residents. This report describes the evaluation and selection of ventilation 

systems for these homes.

Ventilation is clearly a key component in an efficient, healthy home. When improving the energy 

performance of homes—often with increased envelope tightness and insulation—selecting 

ventilation systems is not always straightforward. The ideal ventilation system should be reliable, 

address indoor environmental quality concerns appropriately, be affordable and practical to 

install, consume little energy, and be relatively easy to maintain.

Not surprisingly, such an “ideal” system is hard to come by. Selecting a system involves 

optimizing features depending on the project location, scope, and budget. This report outlines 

key considerations when selecting a ventilation system and reviews findings of several past and 

current studies on the subject. The report then describes CCCRD’s decision process with respect 

to ventilation.

After performing detailed evaluations of several systems, CCCRD has chosen to use local energy 

recovery ventilators in many of its homes. The total installed cost of these systems is manageable 

($700–$1,600), the operating costs are reasonable, and the Consortium for Advanced Residential 

Buildings and CCCRD are confident that these systems will adequately address internal 

environmental quality concerns.
1

1 Introduction

As new home envelopes have become more and more airtight, most in the homebuilding industry 

have come to understand that proper ventilation is critical. With the revisions of ASHRAE 

Standard 62.2 in 2003 (ASHRAE 2003), building scientists and designers had a more meaningful 

standard for single-family ventilation. Many home building programs, such as Leadership in 

Energy and Environmental Design (LEED) for Homes and regional ENERGY STAR®

initiatives, required compliance with ASHRAE 62.2 in new homes.

Building America researchers have been evaluating ventilation systems for more than a decade.

While there is still not universal consensus about which systems perform the best, are the most 

reliable, are most cost-effective for certain homes, there is a wide array of acceptable—if not 

“ideal”—ventilation options.

Until quite recently, most ventilation research efforts have focused on new construction. When 

improving the energy performance of existing homes, ventilation must not be overlooked. Many 

older homes may not experience moisture or indoor environmental quality (IEQ) problems 

because the homes have high levels of uncontrolled infiltration; as envelopes are tightened, 

proper local and whole-building ventilation becomes increasingly important.

Although the basic goals and principles of ventilation are similar in new and existing homes,

selecting and installing ventilation systems in existing homes can be more complex and costly 

than in new construction. Local ventilation (e.g. exhaust fans in baths and kitchens) may perform 

poorly—if they are present at all. Some whole-building ventilation strategies require new ducting 

which can be intrusive and expensive in existing homes.

Figure 1. One of the homes in Las Vegas, Nevada tested with several ventilation systems
2

In this research effort, the Consortium for Advanced Residential Buildings (CARB) has been 

working with Clark County (Nevada) Community Resources Division (CCCRD) to evaluate

optimal ventilation systems in retrofit homes. Through the U.S. Department of Housing and 

Urban Development’s Neighborhood Stabilization Program, CCCRD is purchasing foreclosed 

properties, performing audits, and implementing health, safety, and energy improvements. The 

renovated homes are then rented or sold to qualifying residents. CARB has performed field 

testing, energy modeling, and cost analyses to help CCCRD select ventilation systems that 

reliably provide higher levels of IEQ and minimize first costs, operational costs, and 

maintenance.

Research questions:

• What are the optimal ventilation systems for CCCRD homes with respect to:

o IEQ?

o First costs and ease of installation?

o Energy and operating costs?

o Reliable operation and maintenance?

• What gaps remain in cost and performance of these ventilation systems?

• What additional ventilation products or systems might address some of these gaps?

This report discusses these issues in some detail. Although it focuses on CCCRD homes 

undergoing renovation, the authors hope that the background given and decision-making 

processes will be useful to decision-makers in many other projects.
3

2 Background: Key Ventilation Considerations

2.1 Ventilation Levels and Needs

In CARB’s experience, ANSI/ASHRAE Standard 62.2-2010 (ASHRAE 2010a) is—or is 

becoming—the most common standard referenced for ventilation requirements in homes 

(ventilation in high-rise apartments is covered in Standard 62.1, ASHRAE 2010b). Some 

programs (such as those using Building Performance Institute [BPI] Building Analyst Standards

[BPI 2012b]) still reference the much older ASHRAE Standard 62-89 (ASHRAE 1989).

However, many weatherization and home performance programs are moving toward the more 

recent Standard 62.2. 

Standard 62.2 requires local ventilation in bathrooms (with capacity of at least 50 cubic feet per 

minute [CFM] intermittently or 20 CFM continuously) and kitchens (with capacity of at least 

100 CFM intermittently or 5 air changes per hour [ACH] continuously). These local exhaust 

systems are required to remove odors and pollutants—especially water vapor—from these key 

areas. Although exhaust fans are common in many older homes, in CARB’s experience older 

fans often perform very inefficiently and poorly—exhausting a very small fraction of the design 

or desired flow rates.

Figure 2. Convoluted or extremely long duct runs can dramatically reduce exhaust fan flow rates.

While local exhaust fans can remove water and other pollutants from these heavy source areas, 

Standard 62.2 also requires whole-building ventilation. Whole-building ventilation “is intended 

to dilute the unavoidable contaminant emissions from people, from materials, and from 

background processes” (ASHRAE 2010a). Required whole-building ventilation capacity 
4

(outdoor air [OA] flow rates) depends on home size and number of bedrooms; this is 

summarized in Equation 1.

Qfan = 0.01Afloor+ 7.5(Nbr+1) [1]

where

Qfan = Whole-building ventilation flow rate (continuous) [CFM]

Afloor = Floor area [ft2]

Nbr = Number of bedrooms

ASHRAE 62.2 is a standard for ventilation capacity. Although many whole-building ventilation 

systems are designed to operate continuously or on a timer (e.g. several minutes during each 

hour), ASHRAE 62.2 mandates system capacity only—not how a system is operated.

While ASHRAE 62.2 has been accepted by many builders, designers, and certification programs, 

it is clear that there are situations where the ventilation levels in ASHRAE 62.2 are too high or 

too low. Kitchens in which a great deal of cooking takes place, for example, can benefit from 

higher exhaust levels to keep moisture levels down; new homes with high levels of chemical offgassing may benefit from higher whole-building ventilation levels. Conversely, homes with very 

low occupancy or pollutant generation could save energy by reducing ventilation levels.

The performance of a fan—especially the delivered flow rate—is typically tested and verified 

per HVI (Home Ventilating Institute) Publication 916 (HVI 2009a). These test procedures—and 

the associated certification procedures in HVI Standard 920 (HVI 2009b)—provide standardized 

ratings for most mechanical ventilation fan products used in homes.

HVI also publishes guidelines on recommended ventilation rates in homes (HVI 2011). HVI’s 

recommended ventilation levels are typically higher than those recommended by ASHRAE 62.2.

With kitchen ranges, for example, HVI recommends 100 CFM per linear foot of range width 

(e.g., 250 CFM for a standard 30-in. range). This is considerably higher than the 100 CFM 

minimum specified in ASHRAE 62.2.

2.2 Installation and Integration With Existing Systems

As discussed in Section 1, most past Building America research has focused on ventilation 

systems in new construction. In existing homes, installing whole-building ventilation systems 

can be much more involved and costly—especially with more complicated ventilation systems.

The level of effort, and ultimately the cost, required to install a ventilation system in an existing 

home depend on many factors, including:

• Existing ventilation systems

• Existing ducted heating and/or cooling

• Accessibility to attics and basements

• Scope of the renovation/rehabilitation project.
5

In many instances, existing ventilation systems—especially local ventilation in bathrooms, for 

example—are operable and can be used in the renovated home. Often, however, older fans do 

not deliver desired flow rates—either because the fans themselves operate poorly or because the 

ducts are constricted or obstructed. If the fan is the problem—and the ducts are intact—a 

replacement exhaust fan can often be installed with minimal hassle. A small part of a ceiling or 

wall may need to be refinished, but existing wiring and ducting can minimize the invasiveness,

and ultimately the cost.

In homes with existing forced-air heating or cooling, it’s possible that a central fan-integrated 

supply (CFIS) ventilation system (discussed in Section 4.2) can use the ducts and the central air 

handling unit (AHU).

When there is no existing duct system—or at least none that is appropriate for the desired 

ventilation system—installing new ducts and running electrical service to fans can be time 

consuming and costly. These costs can be minimized when there is access to ventilated areas 

from basements, crawlspaces, or attics. If ducts or electrical lines must be run between floors or 

within walls, sections of wall board or ceilings must generally be removed and replaced. If other 

aspects of the renovation do not necessitate this level of intrusion, this can dramatically increase 

the cost of ventilation installation and integration.

When ventilation is part of very thorough renovations (gut rehabs or deep energy retrofits

[DERs]), these issues may be largely moot. In some large-scope rehab projects, the effort of 

installing and integrating ventilation systems is very similar to what it would be in new 

construction. While running electrical and extensive ducting still represents a substantial cost, the 

incremental costs are much lower in a gut rehab. In practical terms, gut rehabs may allow for 

more intricate or sophisticated ventilation systems that would be impractical or too costly in 

smaller scope renovations.

2.3 Distribution and Mixing of Outdoor Air

Local ventilation is properly targeted toward areas where pollutants, especially moisture, are 

generated intermittently. Whole-building ventilation is intended to reduce pollutants that are 

continuously generated throughout the home. Some ventilation strategies use point-source or 

local ventilation systems to meet whole-building ventilation requirements (e.g., a bath exhaust 

fan running continuously). There is no consensus in the industry about if—or, more accurately, 

when—point-source ventilation is an IEQ liability.

Certainly providing OA to every room in a home is ideal, but the installed costs of such systems 

can be quite high. Below are summaries of several research efforts to evaluate the impact of 

distributing OA or mixing air within a home.

• Rudd (1999) documents tests of two supply-only ventilation systems in new Las Vegas 

homes. The tests revealed that when the ventilation systems are integrated with the central air 

handler (such as with a CFIS system), all areas in the home experience similar air change 

levels. Local supply ventilation did not provide even levels of air changes throughout the 

home; this was especially pronounced when interior doors were closed. When the air handler 

was operated in conjunction with local ventilation, disparities in air change levels were 

substantially reduced.
6

• Rudd and Lstiburek (2000) include the results from Rudd (1999) as well as results from 

testing ventilation systems in a large new home in Minneapolis, Minnesota. During tests of 

local exhaust ventilation used as whole-building ventilation, some areas of the home 

experienced air change rates (or reciprocal age of air [RAoA]) of nearly 50% less than the 

average air change rate in the entire home. When the central air handler was operated 

periodically in conjunction with the exhaust fan, RAoA values were much more uniform. In 

tests of central fan integrated supply ventilation, local RAoA values differed from the home 

average by less than 10%.

• Hendron et al. (2006) document tests in two new homes in Sacramento, California. The tests 

compared exhaust-only ventilation (using a local exhaust fan) and supply ventilation using 

the central air handler and duct system. Ventilation systems were set to meet airflow required 

by ASHRAE Standard 62.2. Multipoint tracer gas tests consistently showed that central fanintegrated supply ventilation provided the lowest variability in age of air from room to room 

(RAoA differences of 0.02 hr-1 or less). Tracer gas tests for exhaust-only systems provided 

the following insights:

o With all doors closed, RAoA values could be quite disparate. In the most extreme 

case, RAoA values differed by a factor of 2.5 between two spaces in the home.

o When doors are open, age-of-air uniformity is much greater. During this test, the 

highest measured RAoA was 15% higher than the lowest RAoA.

o When the central air handler was operated on a 33% duty cycle (without 

introducing additional outside air), RAoA values were nearly as uniform as the 

central AHU-integrated supply ventilation.

• CARB (2007) describes multipoint tracer gas test results in a Massachusetts home with 

exhaust-only ventilation using bathroom fans. Results were similar as those described above:

when interior doors were open, RAoA values were very similar; when doors were closed, 

secondary bedrooms had RAoA values nearly double those of central spaces. Tests also 

included preliminary tests of trickle-vent effectiveness.
7

Figure 3. Summary of RAoA tests from (CARB 2010). In both test cases, all interior doors are 

closed with exhaust ventilation operating continuously. In Case 1, the mixing fan is running.

• The Massachusetts home described in another study (CARB 2010) also had an exhaust-only 

ventilation system. This home, however, had a separate air mixing system. The mixing fan is 

simply an efficient exhaust fan installed in the ceiling of a central space. This fan moves 

approximately 20–30 CFM continuously from the central space to each bedroom. When this 

fan was not running, bedrooms with closed doors experienced RAoA values nearly 50% 

lower than in central spaces. When the mixing fan was running, however, bedroom RAoA 

values were only 10%–15% lower than in central spaces.

• Testing of a CCCRD home is described in (CARB 2011). Two different whole-building 

ventilation systems were installed in this home: an exhaust-only system and a local, ceilingmounted energy recovery ventilator (ERV) (described in Section 4.4). With the local ERV, a 

key goal was to evaluate “short-circuiting” potential, as the supply and exhaust ports are 

located in the same ceiling-mounted device. Tracer gas tests showed that this was not a 

problem in this home.

• Tracer gas tests showed that neither local ventilation system provided equal air change rates 

throughout the home unless interior doors were open or the central air handler fan was 

operating. In the test with the exhaust-only system running with all doors closed, the utility 

room showed RAoA values nearly twice as high as in other spaces; this is concerning as the 

utility room borders the garage.

This list of research is certainly not exhaustive. While the conclusions of the researchers vary (as 

to the viability or appropriateness of various systems), there are some consistent conclusions 

about non-distributed (local or point) ventilation systems. Point ventilation (either exhaust-only 

or H/ERV) provides fairly uniform distribution of fresh air within a home when:

• Doors are open,
8

• A central air handler operates intermittently, or

• A mixing system operates continuously at low volume.

In these three cases, RAoA values in all spaces appear to be similar to RAoA values 

where fully ducted or distributed ventilation is installed. The volumes and duty cycles 

required in the second and third bullets above require more investigation. In the mixing 

study (CARB 2010), 20–30 CFM of continuous mixing proved adequate. It stands to 

reason that a central AHU providing 100 CFM for 15 minutes each hour would provide 

similar results.

• When doors are closed and there is no central air handler operation, air change rates with 

point ventilation vary much more throughout a home. Some areas (especially some 

bedrooms) commonly experience RAoA values 50% lower than do areas where point 

ventilation systems are located.

2.4 Source of Outdoor Air

Certainly OA brought into a home as part of a ventilation system should—as much as possible—

be free from pollutants. With active air intakes, published guidelines (often included as part of a 

manufacturer’s installation instructions) give required clearances from combustion exhausts, 

operable doors and windows, ground or snow level, etc. This concern about the source of OA is 

much more problematic when dealing with exhaust ventilation.

In larger buildings, ventilation systems typically include active makeup air systems to balance air 

exhausted from buildings. Newer residential codes are also starting to require makeup air in 

some cases. In the 2009 International Residential Code, for example, any local exhaust fans with 

capacity of 400 CFM or higher must include makeup air provisions (ICC 2009).

In smaller, existing homes, makeup air provisions are rare. By design or by default, most exhaust 

ventilation systems force infiltration through building envelopes. This may not be ideal, but there 

is not widespread consensus on whether this practice is acceptable in any circumstance. Most 

professionals do agree, however, that these situations or configurations are far from ideal:

• Depressurizing the home can interfere with natural-draft combustion appliances.

• In a home with an attached garage, forced infiltration can enter a home through the garage.

With the air can come traces of car exhaust, fuel, or solvents that may be stored in the garage.

This potential problem was identified during tracer gas testing of a CCCRD home (CARB 

2011).

• In a home with a moist or moldy crawlspace or basement, makeup air coming through such a 

space may bring mold spores, humidity, or other undesirable pollutants.

• In some cases, depressurizing a home can exacerbate introduction of radon or soil gas 

through the foundation.

These can be serious issues, and in some of these situations exhaust ventilation—without 

makeup air provisions—should be avoided. In many cases, however, these issues can be 

addressed with common-sense solutions:

• Eliminate natural-draft combustion appliances.
9

• Meticulously air seal the garage from the living space and/or install ventilation in the garage 

that eliminates the positive pressure with respect to the living space.

• Create a well-sealed, dry, conditioned crawlspace or basement.

• Install a radon mitigation system if soil gas is a problem.

All homes require exhaust ventilation, if only intermittently (e.g., to meet local ventilation 

requirements of ASHRAE 62.2). The concerns above become somewhat more pressing when 

exhaust ventilation is used for whole-building ventilation and runs continuously.

2.5 Energy Implications

Mechanical ventilation systems have two key energy impacts:

• Electricity used to operate fans and ventilation equipment.

• Thermal energy required to condition OA introduced into the space.

Electrical fan energy varies widely. Typical range for bath exhaust fan power is 6–40 Watts.

Conventional HRV and ERV power consumption ranges from 40 to 200 Watts. The fan in a 

central air handler or furnace—used in some ventilation strategies—can use 200–700 Watts.

These are very general ranges, and power consumption certainly varies with air flow and system 

curves. Power consumption also, not surprisingly, varies with cost. Typically the lowest power 

ventilation products use fans with electronically commutated motors (ECMs) which often mean 

higher costs.

The second point—conditioning the introduced OA—is climate dependent. HRVs and ERVs can 

certainly mitigate this effect. The sensible effectiveness of ERV and HRV heat exchangers 

typically ranges from 55% to 85%. Again, the higher values typically come with a higher cost.

More extreme outdoor temperatures result in greater benefits from heat recovery. In humid 

climates, the latent transfer of ERVs can help significantly to manage the latent loads introduced 

by a ventilation system.

For CCCRD homes in Las Vegas, the energy-related specifications of the ventilation systems 

investigated—along with the modeled energy impacts—are outlined in Section 4.

2.6 Operation and Maintenance

One important—though sometimes overlooked—aspect of a ventilation system is the level of 

maintenance required. All mechanical systems require some maintenance, but maintenance 

required on ventilation systems can vary greatly. On one end of this spectrum, local bathroom 

exhaust fans have very modest maintenance requirements. Typical maintenance instructions 

are—at least once per year—to clean and/or wipe the exhaust fan grille, vacuum dust and dirt 

from the fan body, wipe the fan body clean, and replace the grille (Panasonic).

Some of the higher performing ERVs, by contrast, require quarterly checking or cleaning of 

filters, heat exchange media, and exterior duct terminations. While exhaust fan maintenance 

instructions may consist of four or five short bullets, instructions for checking and cleaning ERV 

components are typically several pages (UltimateAir 2006). This increased level of maintenance 

is not a design flaw; it is simply necessary with more complex systems.
10

CARB has worked with several builders and developers who are very sensitive to the level of 

maintenance required in their homes. Ventilation systems are often of special concern, as a 

malfunctioning ventilation system in a tight, efficient home can lead to moisture, mold, and other 

problems. If systems are not maintained, ventilation flow rates will often decrease over time—

eventually to a small fraction of the design rates. To minimize these risks, some builders actively 

choose ventilation systems with lower maintenance requirements. Lower-maintenance systems 

also tend to have lower first costs; this certainly factors into decision processes. Costs are 

discussed in Section 4.
11

3 What Systems Are Being Installed?

Through direct experience and literature reviews, CARB has documented trends in how 

mechanical ventilation is addressed when improving existing homes. Substantial information is 

available for two main types of home improvement efforts:

• Weatherization (or similar): typically lower cost, nonintrusive energy and IEQ 

improvements.

• Deep energy retrofits (or similar): usually much more intensive—and expensive—

improvements to existing homes. These are often custom projects and sometimes gut 

rehabilitation projects.

There is, of course, a wide spectrum of home improvement efforts, but these two areas currently 

have increased focus in the home energy improvement markets.

3.1 Weatherization and Similar Programs

The term weatherization can broadly refer to improving the energy and comfort performance of a 

home, but weatherization programs typically offer modest home improvements for lower income 

occupants. Generally speaking, these programs often include basic safety tests and diagnostics, 

air sealing, added insulation, efficient lighting, water saving measures, and possible appliance 

upgrades. Weatherization is usually performed on occupied homes, and the home improvement 

efforts are not usually extensive or intrusive.

How weatherization programs address ventilation certainly varies, but many programs use 

standards developed by the Building Performance Institute (BPI) or similar standards. The core 

BPI standard (BPI 2012b) references ASHRAE 62-89 (ASHRAE 1989). Such weatherization 

standards require whole-building ventilation only when natural infiltration is lower than a 

defined benchmark. This benchmark, referred to as the Building Airflow Standard (BAS) in BPI 

Standards, is the greater of:

• 0.35 air changes per hour (ACH)

• 15 CFM per occupant.

These values are converted to equivalent envelope leakages as measured with a blower door. For 

example, a 1,500-ft2

, 12,750-ft3, two-occupant, single-story home in Las Vegas would have a 

BAS of 74 CFM. When depressurizing with a blower door at 50 Pa, the BAS becomes 1,599 

CFM50 (see BPI 2012b for information on these calculations).

Following the BPI standards, when testing this example home a weatherization contractor should

follow this protocol:

• If blower door test show infiltration above 1,599 CFM50, no action need be taken concerning 

ventilation.

• If blower door tests show infiltration less than 1,599 CFM50 but higher than 1,119 CFM50

(70% of BAS), ventilation must be recommended.
12

• If blower door tests show infiltration less than 1,119 CFM50 (70% of BAS), a ventilation 

system must be installed as part of weatherization work.

The requirements are fairly clearly laid out, but most home performance and weatherization 

contractors are equipped to handle air sealing, insulating, lighting upgrades, etc. They are not 

equipped to handle HVAC improvements. In fact upgrading ventilation is outside the scope of 

many home performance programs (it is an IEQ measure, not strictly an energy-saving measure, 

and is therefore often outside the approved scope of services). With these caveats, the effective 

weatherization guidelines (with respect to ventilation) become:

• Do not air seal a home below the BAS value.

• If initial tests of a home show envelope leakage below the BAS, walk away from the home.

Although this is rarely publicized, in CARB’s experience this is the de facto rule for many 

weatherization and home performance programs. Building America goals require reaching for 

higher levels of efficiency and envelope tightness. To reach these higher levels, ventilation 

cannot be ignored. Fortunately, there seems to be a growing trend to address ventilation 

differently. Several agencies are aligning program rules with ASHRAE 62.2 or similar standards.

In response, BPI has announced adjusting its standards in 2013 (BPI 2012a).

3.2 Deep Energy Retrofits and Similar Projects

While weatherization programs often do not result in envelope tightness where standards would 

require whole-building ventilation, more intense energy improvement efforts—such as DERs—

certainly do achieve lower infiltration levels where whole-building ventilation is necessary.

There are several regional DER programs. One nation-wide (and beyond) effort is the “1000 

Home Challenge” sponsored by Affordable Comfort, Inc. (thousandhomechallenge.com). This 

initiative encourages reductions in home energy consumption of at least 70%. Achieving these 

reductions typically requires dramatic envelope improvements, HVAC system upgrades, 

efficient lights and appliances, and changes in occupant awareness and behavior. Good 

ventilation is critical in such tight envelopes.

A survey of the case studies on the 1000-Home Challenge site (ACI 2012) shows that more than

75% of DER projects incorporate HRVs or ERVs to provide whole-building ventilation. Cost 

information is not consistently available for these projects, but the scope of the home energy 

improvements shows that overall budgets are considerable. The higher budgets—along with the 

intensive nature of the energy improvements—allows for easier incorporation of more 

complicated HRV or ERV systems.

In Massachusetts, National Grid, one of the largest utilities in the state, recently sponsored a 

DER pilot project. Among the first three completed projects (with case studies available), two 

homes use ERVs and one uses a CFIS system (BSC 2010, BSC 2011a, BSC 2011b).
13

Figure 4. With significant space and ducting requirements, fully ducted ERV or HRV systems are 

often more practical in major renovation projects. 

3.3 Midrange Energy Improvement Efforts

The examples above—weatherization efforts and DERs—represent a fairly broad spectrum in 

home energy improvements. Building America goals target efforts somewhere in the middle of 

this range. Most DERs certainly meet Building America energy goals, but the high cost of most 

of these efforts limits widespread adoption or duplication. On the flip side, weatherization often 

addresses only the very low-hanging fruit; Building America is pushing for more significant 

energy improvements.

The CCCRD homes in Las Vegas fit squarely in the middle of this range: CCCRD has much 

more rigorous energy goals than most weatherization programs (HERS 50, though that is not 

consistently attained), but with smaller scope (and certainly budget) than many DER projects.

One of CARB’s efforts with CCCRD has been evaluating and helping to optimize its approach to 

ventilation.
14

4 Systems Evaluated and Cost Analysis

Below are descriptions of four ventilation systems considered for CCCRD homes along with

associated advantages, disadvantages, installation costs, and operating costs:

• Exhaust only

• CFIS (central fan-integrated supply)

• Ducted ERV or HRV

• Local ERV.

4.1 Exhaust Ventilation

Most exhaust fans in existing homes are not terribly efficient, quiet, or rated for continuous 

operation. In such cases, if exhaust ventilation is to be used as a whole-building ventilation 

strategy, exhaust fans must be replaced or added as appropriate.

CCCRD’s standard practice with local exhaust ventilation is to keep the fans in place when they 

are working adequately to provide local ventilation. However, it is rather rare to find local 

exhaust fans working properly. In some instances, CCCRD has replaced older bathroom exhaust 

fans with Panasonic WhisperGreen fans designed to run continuously to provide whole-building 

ventilation. The installed cost of these fans is approximately $400; this exhaust only strategy has

the lowest first-cost of all systems considered.

Figure 5. New bathroom exhaust fan installed in a CCCRD home

Power consumption of these fans is very modest—typically 6–8 Watts when exhausting 50 

CFM. Running continuously over an entire year, the fan would require 50–70 kWh of electric 

energy. Thermal impacts are discussed in Section 4.5.

The key advantages of the exhaust-only approach have already been mentioned: low first-cost, 

ease of installation, low maintenance, and modest operating cost. The drawbacks are:
15

• OA is not distributed evenly to all parts of the home. Past research has shown that when 

doors are open or when a forced-air heating or cooling system is operating, this point is moot.

As all CCCRD homes use forced-air heating and cooling systems (and typically new, 

properly sized, well-balanced systems), this was not a major concern.

• By depressurizing the home, there is potential to draw air from undesirable spaces. Because 

there is no atmospheric combustion appliance in the conditioned space, there is no risk of 

backdrafting or similar combustion problems. Most of these homes do, however, have 

attached garages, and rigorous sealing of the walls and ceilings of the garages is typically not 

in the project scope or budget. As CARB’s testing showed (CARB 2011), infiltration through 

the garage likely accounts for some portion of the makeup air from an exhaust system.

CCCRD has used exhaust-only ventilation in some homes, but concerns about drawing in air 

from garages—and about not achieving any heat recovery—have led them to explore other 

options.

4.2 Central Fan Integrated Supply

As all CCCRD homes have forced-air heating and cooling systems, CFIS was an obvious system 

to investigate. Its installed cost is relatively modest: approximately $650. CFIS addresses two 

concerns with exhaust ventilation: (1) drawing in contaminated air from the garage, and (2) not 

distributing OA throughout the home. The key detriment of CFIS is the electricity required to 

operate the air handler fan. Even with a very efficient fan—which may consume 300 Watts—

operating a CFIS system on a 50% duty-cycle would result in additional electricity use of 750–

1000 kWh/yr. This added operating cost—along with its associated impact on HERS indices—

was the reason CCCRD did not pursue this strategy.

Figure 6. Simple schematic of CFIS ventilation system

4.3 Ducted Energy or Heat Recovery Ventilator

In a hot, humid climate, an ERV is recommended as it will remove some of the moisture in the 

incoming airstream (transferring it to the relatively cool, dry exhaust stream). In a dry climate 
16

such as Las Vegas, this benefit is largely moot, and the choice between ERVs and HRVs is not 

always clear (Holladay 2009). In this arid climate, the indoor humidity (both relative and 

absolute) will usually be higher than the OA humidity. When this is the case, an HRV, 

recovering only sensible heat, will tend to reduce indoor humidity year-round. An ERV, on the 

other hand, will tend to retain some of this interior moisture. This may be a benefit or a 

detriment, depending on lifestyles and occupant behavior.

Installation costs of the systems, however, are quite similar. CARB and CCCRD estimated that a 

fully ducted ERV/HRV system (separate from the heating and cooling duct system) would cost 

$1,000–$1,500 to install in a single-story home. Installation requires supply and exhaust ducts to 

outdoors with exterior terminals as well as ducts and registers supplying and exhausting from 

several parts of the home. In the Las Vegas homes evaluated, most ducts would be installed in 

the attic; installation could be considerably more costly if portions of walls or ceilings were 

removed for installation.

This installation cost is separate from the cost of the core hardware: the HRV or ERV unit. These 

hardware costs can vary greatly. One more affordable HRV which CARB has seen used in 

several homes is the FanTech SH704. Although performance varies based on the installation and 

duct system, this delivers approximately 60 CFM, consumes 40 Watts, has a sensible recovery 

efficiency of 55%, and has an apparent sensible effectiveness of 63%. This unit costs 

approximately $450.

One of the more efficient—though more costly—ERVs that CARB has used on several projects 

is the Ultimateair Recoupaerator. This unit has variable-speed motors, and at 70 CFM it 

consumes approximately 40 Watts. This unit has a published sensible recovery efficiency of 

83%, apparent sensible effectiveness of 96%, total recovery efficiency of 55% (during cooling), 

and a list price of approximately $1,800.

HRVs and ERVs with ducted distribution address most ventilation performance issues:

• Balanced distribution avoids drawing in air from unknown or unsafe sources.

• Ducted distribution brings OA to all parts of the home.

• Heat recovery limits additional load on the heating and cooling systems.

Operating costs of HRVs are very dependent on climate and the benefits of heat recovery.

Operating a 40-Watt appliance on a 70% duty cycle consumes 245 kWh/yr. The thermal impacts 

for an example Las Vegas home are discussed in Section 4.5. In addition to costs, maintenance 

for these systems is not insignificant. Most HRV/ERVs have filters and/or media that need to be 

cleaned or replaced regularly; failure to do this can result in dramatic drops in performance (air 

flow rates, heat exchange efficiency, and equipment durability). 

The key drawbacks of these systems—and the reasons CCCRD did not actively pursue any of 

these options—are first cost and installation requirements. Depending on equipment chosen and 

configuration, such a system would cost $1,450–$3,300 for a single-story home. In a two-story 

home, if ducts were run from the attic to supply or exhaust from the first floor, installation costs 

would certainly be higher. The amount of this increase would vary greatly depending on the 
17

home layout, areas of wall board or ceilings, etc. needing to be removed and patched; and the 

scope of the renovation project.

4.4 Local Energy Recovery Ventilator

The final system considered by CCCRD, and the system CCCRD started to use quite often, is a 

new, local ERV. This product, the Panasonic WhisperComfort, is installed in a ceiling cavity. It 

requires one fresh air duct and one exhaust duct, both run to outdoor terminations. The fresh air 

is supplied to the home and the indoor air is exhausted from the ceiling-mounted unit.

The immediate concern for many is short-circuiting—fresh air immediately being exhausted as 

the delivery and exhaust locations are so close together. CARB’s testing of the unit, however, 

showed that this was not a significant concern (CARB 2011).

The WhisperComfort costs CCCRD $700–$800 to purchase and install. On its highest speed, the 

unit draws 23 Watts, exhausts 40 CFM, and supplies 30 CFM (both at 0.1 in. w.g.). Published 

heat recovery efficiencies are 66% during heating season (apparent sensible effectiveness) and 

36% during cooling (total recovery efficiency).

Figure 7. Images of Panasonic’s WhisperComfort ERV. At right, installed (with cover removed) in 

the ceiling of a CCCRD home

The unit is compact, relatively simple to install (especially in the top floor of a home where the 

attic is accessible), does not consume a large amount of electricity, and offers some heat 

recovery (although at modest efficiencies). There are several limitations to using this product for 

whole-building ventilation, some of which are evident from the specifications.

• The maximum exhaust flow rate is 40 CFM (the maximum supply is 30 CFM). There are few 

single-family, detached homes for which 40 CFM meets the whole-building ventilation rates 

prescribed by ASHRAE 62.2. Some CCCRD homes employing this strategy require two 

local ERVs.

• Unlike some of Panasonic’s exhaust fans, WhisperComfort units do not use ECMs. Rated 

flows are at 0.1-in. w.g., and relatively short, straight duct runs are important.
18

• The device avoids freezing and defrosting problems by switching to exhaust only when 

outdoor temperatures are below 20°F. When outdoor temperature is between 20° and 32°F, it

cycles between balanced and exhaust-only ventilation.

Continuous exhaust ventilation may lead to issues as discussed in Section 2.4, but issues 

would likely be much less severe with this ERV unit. Natural-draft combustion appliances 

have much better draft during cold weather, and introduction of pollutants (from garages, 

etc.) would be much less frequent than with dedicated exhaust-only systems. In Las Vegas, 

where the heating design temperature is 32°F, these concerns are trivial.

• As mentioned above, the unit’s design does not allow a significant amount of fresh air to 

short-circuit (and be immediately exhausted). CARB’s and NREL’s tracer gas testing 

confirmed this. However, this unit certainly is a local ventilator. It provides fresh air to one 

location; it does not actively distribute fresh air throughout a home.

Table 1. Overview of Whole-Building Ventilation Systems Evaluated and 

Considered in CCCRD Homes

System Power

Approximate 

Installed Cost

($)

Advantages Disadvantages

Exhaust Fan 

Operating 

Continuously

6 W 400

• Low first cost

• Simplest installation

• Low operating cost

• Lowest maintenance

• May draw air in 

from garage

• OA not actively 

distributed

CFIS

Depends on 

AHU, 250 W 

minimum

650

• Low first cost

• Simple installation

• Distributed OA

• High operating 

cost

Distributed 

ERV/HRV

Varies, at least 

40 W 1,450–3,300

• Distributed OA

• Heat recovery

• Potential for low 

operating cost

• High first cost

• More complex 

installation

• Highest 

maintenance

Local ERV 23 W 750 • Heat recovery

• Low operating cost

• OA not 

distributed

4.5 Cost Comparisons

To compare the costs of these ventilation systems in the context of this report, CARB has 

performed modeling on an example CCCRD home: 1,780 ft2, two-story, three-bedroom, with 

blower door tests showing infiltration of 810 CFM50. The home has a 92%-AFUE gas furnace 

and a 16-SEER air conditioner. In this example, all local ventilation systems (bathroom and 

kitchen) are assumed to be installed and operational (therefore they do not enter into wholebuilding ventilation cost analyses).

Per ASHRAE 62.2-2010, this home requires a whole-building ventilation capacity of 48 CFM.

Table 2 describes four systems evaluated along with approximate installed, operating, and 

annualized costs. Operating costs include fan electricity and additional space conditioning loads 
19

($0.109/kWh, $1.09/therm). Annualized costs include operating costs as well as annualized cost 

of the installed system over 15 years with a discount rate of 3%.

Table 2. Cost Comparisons for Several Ventilation Systems 

Considered in an Example Las Vegas Home

Whole-Building 

Ventilation 

System

Description Installed 

Cost

Annual 

Operating 

Cost

Annualized 

Cost

None For reference only $0 $0 $0

Exhaust Only

Panasonic WhisperGreen FV08VKS3 operating continuously at 

50 CFM, 7 W

$400 $30 $64

CFIS OA duct provides 80 CFM, set to 

run 15 h/day, AHU fan uses 300 W $650 $146 $200

Ducted HRV Fantech SH704 running 

continuously at 60 CFM, 40 W $2,250 $64 $252

Local ERVs

Two Panasonic WhisperComfort 

ERVs, each running continuously at 

30 CFM, 21 W each

$1,500 $61 $187

5 Conclusions

In the examples shown in Table 2, the low annualized cost of the exhaust-only system is striking.

Cost is not, however, the only criterion. The risk of drawing in air through attached garages is a 

significant concern. The lack of OA distribution—another common drawback to the exhaustonly approach—is a lesser concern with the forced-air heating and cooling systems in these 

homes. Of course, the forced-air heating and cooling system will operate only when there is a 

thermal load. Adding controls for intermittent mixing operation was not considered here, but this 

practice may have merit.

While the annualized cost of the CFIS system is quite comparable to that of the local ERV, the 

high energy consumption of this system eliminated it from consideration. The two ERV/HRV 

options have very similar operating costs, but the simpler installation and lower installed costs of 

the local ERV give this system an edge.

Moving forward, CCCRD has chosen to use the local ERV system in most of its renovation 

projects. The lack of fresh air distribution may be the largest drawback of this system, but this 

concern is reduced with forced-air heating and cooling systems in all homes.
20

6 Discussion

6.1 Other Projects and Climates

Section 2 attempted to present much previous and current work and to outline many issues 

related to ventilation systems. The authors hope that this information is useful to many users in 

many climates, but the focus of the study was on CCCRD homes in and near Las Vegas, Nevada.

The results could be considerably different for a single-family home in south Texas or for an 

apartment in Chicago.

There is a group of key questions that should be asked when selecting a whole-building 

ventilation system for an existing home. Several of these questions, and some example

implications, are presented here:

• What climate? The benefits of HRVs and ERVs will increase in extreme climates. In hot, 

humid climates, the latent load introduced by ventilation may influence design of other 

HVAC systems.

• What is the scope of the rehab/renovation project? More intensive projects may allow for 

more robust ventilation systems at more reasonable costs. In a gut rehab, it is usually much 

simpler to incorporate new duct systems. If renovations are more modest, any removal (and 

replacement) of ceilings or wallboard may increase costs considerably.

• Will any natural draft combustion appliances be inside the home’s pressure boundary?

This is a key concern for any exhaust ventilation.

• Is there a crawlspace, attached garage, or other attached space that may contain 

pollutants? This again may be a concern for exhaust ventilation

• What type of heating and cooling system? A forced-air heating and cooling system may 

reduce concerns related to non-distributed ventilation.

• What is the expected energy performance level of the home? Providing ventilation—and 

fresh air mixing or distribution—may be even more important in a very low-load, airtight

home.

In conjunction with questions about the project, the goals of the project should also be 

considered:

• What is the budget?

• What ventilation rates or standards or program requirements are targeted?

• How important is energy/operating cost? In relation to first cost?

• What maintenance levels are appropriate or acceptable?

There is no one-size-fits-all solution to ventilation, especially in existing homes. CARB plans to 

develop guidelines—useful to remodelers, contractors, and programs—for addressing ventilation 

in existing homes. The guidelines will step through these questions above, among others, and 

present viable ventilation system options along with the advantages, disadvantages, and costs 

that go with them.
21

6.2 Gaps and Additional Systems

All the ventilation systems discussed have advantages and disadvantages, and there’s rarely a 

“silver bullet” approach that solves all cost and performance concerns. In working with builder 

and manufacturer partners, CARB has identified several systems or product needs that might 

alleviate some concerns.

6.2.1 Larger Capacity Local Energy Recovery Ventilator

Test results of Panasonic’s WhisperComfort ERV were quite positive. One limiting aspect of the 

device is its flow rates: maximum exhaust rate is 40 CFM, maximum supply rate is 30 CFM.

Although 40 CFM can meet ASHRAE 62.2 whole-building ventilation rates for many twobedroom homes (up to 1,750 ft2

), three-bedroom homes and larger typically require higher flow 

rates.

Installing two local ERVs, as CCCRD does in many homes, is certainly a solution, and this 

practice helps to address concerns about OA distribution. But a larger capacity unit could 

significantly reduce costs in some scenarios. CARB believes that the capacity of this ERV is 

limited by its size; it is designed to fit in a floor cavity of 2 × 6 joists at 16 in. on center. Larger 

air flow capacity would require a bigger unit, larger dimensions, and larger ducts (likely moving 

to 6 in. diameter from 4 in.). The larger size may make such a unit impractical for many 

installations.

6.2.2 Energy Recovery Ventilator With Limited Ducting

Perhaps the biggest potential disadvantage of the local ERV is the lack of OA distribution. The 

Panasonic WhisperComfort exhausts from and supplies OA to a single location. There is no 

consensus among building scientists about the importance of distributing or mixing fresh air (see 

Section 2.3), but distributing OA more evenly is certainly preferred.

Panasonic has discussed the development of a modified version of the WhisperComfort: a 

ceiling-mounted unit that supplies air directly to the room below but exhausts air through a 4-in.

duct connection. By running this exhaust duct to one or two separate locations within the 

home—keeping pressure drop in mind—OA distribution or mixing could be dramatically 

improved. CARB had hoped to install and test a prototype of this system, but the product’s

development has been delayed.

6.2.3 Mixing

Several tracer gas studies (see Section 2.3) have shown that when a home’s central air handler 

operates for heating or cooling, concentrations of tracer gas “pollutants” are equalized 

throughout the home. Homes without forced-air heating or cooling (hydronic heating, mini-split 

heat pumps, etc.) are much more prone to variations in pollutant concentrations. Some of these 

same tests, however, have shown that a very modest level of distribution or “mixing” of air 

within the home can alleviate these concerns. In one study (CARB 2010), delivering 20–30 CFM

to each bedroom from a central living space dramatically reduced—nearly eliminated—

variations in tracer gas concentrations. CARB believes that more study is merited to determine 

what minimum levels of mixing are appropriate to alleviate IEQ concerns. Similarly, more study 

on how often a central forced-air heating/cooling system must operate—and at what flow rates—

to alleviate IEQ concerns would be very helpful in designing and selecting ventilation systems.
22

The term mixing is used here to describe simply moving conditioned, indoor air from one space 

to another. Conventional distribution, on the other hand, delivers heated, cooled, or fresh air 

directly to spaces in a home. Several Building America teams have been investigating the 

impacts of such mixing systems on temperature and comfort in homes with simple, nondistributed heating and cooling systems (ductless heat pumps, room heaters, etc.).

These mixing systems can be smaller and less costly than conventional distribution systems.

When thermal loads are small enough, local heating, cooling, and ventilation systems—

combined with mixing systems—can provide efficiency and comfort at much lower costs. CARB 

is investigating this further with several partners.
23

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