Zero Energy Ready Home 

Multifamily Case Study 

Analysis 

Jordan Dentz and Kunal Alaigh

Advanced Residential Integrated Energy 

Solutions Collaborative 

February 2016
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iii

Zero Energy Ready Home Multifamily Case Study Analysis 

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: 

Jordan Dentz and Kunal Alaigh 

Advanced Residential Integrated Energy Solutions Collaborative 

The Levy Partnership, Inc. 

1776 Broadway, Suite 2205 

New York, NY 10019 

NREL Technical Monitor: Stacey Rothgeb 

Prepared under Subcontract No. KNDJ-0-40347-05 

February 2016
iv

The work presented in this report does not represent 

performance of any product relative to regulated 

minimum efficiency requirements.

The laboratory and/or field sites used for this work are 

not certified rating test facilities. The conditions and 

methods under which products were characterized for 

this work differ from standard rating conditions, as 

described.

Because the methods and conditions differ, the reported 

results are not comparable to rated product performance 

and should only be used to estimate performance under 

the measured conditions.
v

Contents

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

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

Definitions.................................................................................................................................................. vii

Acknowledgments ................................................................................................................................... viii

Executive Summary................................................................................................................................... ix

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

1.1 Background...................................................................................................................................... 1

1.2 Zero Energy Ready Home Requirements ........................................................................................ 2

1.2.1 Relevance to Building America’s Goals............................................................................. 3

1.2.2 Research Questions............................................................................................................. 4

2 Technical Approach ............................................................................................................................. 5

3 Analysis ................................................................................................................................................. 6

3.1 Original Specifications..................................................................................................................... 6

3.2 Zero Energy Ready Home Compliance ........................................................................................... 7

3.3 Design Changes ............................................................................................................................. 10

3.3.1 Thermal Envelope............................................................................................................. 10

3.3.2 Domestic Hot Water Distribution Efficiency.................................................................... 10

3.3.4 Garage Exhaust Fan .......................................................................................................... 16

3.3.5 Equipment Sizing Reduction ............................................................................................ 16

3.3.6 Summary of Design Changes............................................................................................ 17

4 Modeling.............................................................................................................................................. 18

5 Results and Discussion..................................................................................................................... 23

5.1 Cost-Effectiveness......................................................................................................................... 23

5.2 Impacts and Trade-Offs ................................................................................................................. 23

6 Conclusions ........................................................................................................................................ 25

References................................................................................................................................................. 27

Appendix.................................................................................................................................................... 29
vi

List of Figures

Figure 1. Avalon Green III under construction......................................................................................... 2

Figure 2. New privately owned housing units authorized by building permits in permit-issuing 

places—national ................................................................................................................................... 2

Figure 3. Two-bedroom apartment—water heater relocation............................................................... 11

Figure 4. Two-bedroom townhome—water heater relocation.............................................................. 11

Figure 5. Townhome unit ductwork—revisions in red.......................................................................... 15

Figure 6. Apartment source energy use from BEopt ............................................................................ 19

Figure 7. Townhome source energy use from BEopt ........................................................................... 20

Figure 8. Apartment (single unit B4) annualized energy-related costs from BEopt.......................... 21

Figure 9. Townhome (single unit TC3) annualized energy-related costs from BEopt....................... 21

Unless otherwise noted, all figures were created by the ARIES team.

List of Tables

Table 1. ZERH Requirements..................................................................................................................... 3

Table 2. ENERGY STAR Reference Design Compared to Original Specification—

Thermal Envelope................................................................................................................................. 6

Table 3. Original Specification—Equipment ............................................................................................ 7

Table 4. UA of Original Specifications Compared to ZERH.................................................................... 7

Table 5. Major ZERH Mandatory Requirements Compared to Original Design.................................... 8

Table 6. Major Indoor airPLUS Mandatory Requirements Compared to Original Design ................... 9

Table 7. Improvement to Whole-Envelope UA with Added Exterior Rigid Insulation........................ 10

Table 8. Change in Vent and Heat Loop Piping Distance (in feet) and Cost Implications ................ 12

Table 9. Apartment DHW Zones .............................................................................................................. 13

Table 10. Apartment DHW Distribution Water and Energy Waste per Year........................................ 13

Table 11. Townhome DHW Zones (ZERH version) ................................................................................ 14

Table 12. Townhome DHW Distribution Water and Energy Waste per Year....................................... 14

Table 13. Space-Conditioning Equipment Sizing Reduction................................................................ 16

Table 14. Design Changes........................................................................................................................ 17

Table 15. Incremental Costs—Original Design to ZERH....................................................................... 18

Table 16. Additional Incremental Costs—ENERGY STAR Version 3 Baseline to ZERH ................... 19

Table 17. Utility Rates............................................................................................................................... 22

Table 18. Projected Annual Utility Bill Savings for the Original and ZERH Designs ......................... 22

Table 19. HERS Indices for Original and ZERH Designs ...................................................................... 22

Table 20. Total Incremental Costs from Original Design to ZERH....................................................... 23

Table 21. Total Incremental Costs from ENERGY STAR Version 3 Minimum Design to ZERH........ 23

Table 22. Impacts and Trade-Offs for Each Design Change................................................................. 24

Table 23. Inputs and Results—DHW Distribution Waste—Apartment ................................................ 30

Table 24. Inputs and Results—DHW Distribution Waste—Townhome ............................................... 31

Unless otherwise noted, all tables were created by the ARIES team.
vii

Definitions

AFUE Annual Fuel Utilization Efficiency

ARIES Advanced Residential Integrated Energy Solutions 

Collaborative Building America Team

BEoptTM Building Energy Optimization software

BTU British Thermal Unit

CFL Compact Fluorescent Lamp

CFM Cubic Feet per Minute

DHW Domestic Hot Water

DOE U.S. Department of Energy

EF Energy Factor

EPA Environmental Protection Agency

HVAC Heating Ventilating, and Air Conditioning

HERS Home Energy Rating System

IECC International Energy Conservation Code

IEQ Indoor Environmental Quality

MERV Minimum Efficiency Reporting Value

NYSERDA New York State Energy Research and Development Authority

PEX Cross-Linked Polyethylene

SEER Seasonal Energy-Efficiency Ratio

TO5 Task Order 5

UA Area-Weighted Average Thermal Conductivity

ZERH Zero Energy Ready Home
viii

Acknowledgments

The authors would like to express their gratitude to Mitchel Forlenza and Aaron Levy of 

AvalonBay Communities for their assistance in facilitating this study. The authors also thank 

Michael Gestwick and Stacey Rothgeb of the National Renewable Energy Laboratory, who 

oversaw this work on behalf of the U.S. Department of Energy’s Building America program.
ix

Executive Summary

The U.S. Department of Energy’s Zero Energy Ready Home (ZERH) recognition program builds 

upon the building science requirements of ENERGY STAR® Certified Homes, Version 3 and 

best practices tested by the Building America research and demonstration program. The 

objectives of the ZERH criteria are to increase energy efficiency, improve indoor air quality, and 

prepare homes so renewable power can cost-effectively offset most or all of their annual energy 

consumption.

Multifamily units (units in buildings with five or more apartments) comprise an increasingly 

important segment in the U.S. new housing market. Over the past 30 years, this segment has 

averaged 24% of residential building permits and since the recession in 2008 averages 34% of 

new residential building permits (U.S. Census Bureau n.d.). AvalonBay Communities is a large 

multifamily developer that worked with the U.S. Department of Energy’s Building America 

research team Advanced Residential Integrated Energy Solutions Collaborative (ARIES) to 

create a ZERH specification for a new development that was targeting ENERGY STAR 

certification.

ARIES undertook this research to analyze the cost, constructability, and energy implications of 

upgrading from ENERGY STAR to the ZERH specification for low-rise multifamily and 

attached housing units in climate zone 4. The effort serves as an example of what multifamily 

builders can achieve and evaluates the mainstream viability of ZERH building practices. The 

team used Building Energy Optimization (BEoptTM) software to select sample apartment units 

for energy modeling and cost analysis and to determine savings and construction cost increases 

compared to ENERGY STAR.

Starting from the original ENERGY STAR-compliant design (Version 3, Rev. 07), seven 

changes would need to be made in the sampled units to comply with ZERH criteria: 

• Increase the exterior rigid insulation thickness from 1⁄2 in. to 1 in. 

• Relocate the water heaters. 

• Bring the ducts into a dropped soffit in townhome units. 

• Upgrade to minimum efficiency reporting value 8 filters. 

• Add rodent screens to vents. 

• Protect and clean ducts. 

• Install an exhaust fan in the garage of each townhome unit. 

All these design upgrades could have been incorporated relatively easily any time before 

construction; however, the domestic hot water distribution and duct location changes would 

optimally be made during the design phase. Energy impacts of upgrading from the original 

design to ZERH included a reduction in source energy consumption of 2%–8% or 1.7–10.4 

MBtu/year. Because of local program requirements, the original design was already about 8% 

better than a design configured to minimum ENERGY STAR criteria. According to the BEopt 

analysis, annualized energy-related costs (the annual costs of all energy-related expenses 
x

including utilities, mortgages on equipment, etc.)1 of the ZERH design were approximately $12 

lower for the apartment and approximately $134 lower for the townhome than for the original 

design.

The residents pay for all utilities in these rental apartments, so the savings would accrue to the 

residents; the construction costs would be borne by the developer. The developer would be 

motivated to make these improvements only if they increased marketability, raised rents, 

increased occupant satisfaction, or reduced maintenance costs.

 1 BEopt calculates the annualized energy-related costs by annualizing the energy-related cash flows over the 

analysis period. Cash flows consist of mortgage or loan payments, replacement costs, utility bill payments, mortgage 

tax deductions (for new construction), and residual values. Costs, excluding mortgage or loan payments, are inflated 

based on the time they occur during the analysis period. The cash flows are annualized by determining the present 

worth of the cash flow by converting the total cost for each year to the value at the beginning of the analysis period

(NREL 2012).
1

1 Introduction

1.1 Background

The U.S. Department of Energy’s (DOE’s) Zero Energy Ready Home (ZERH) program 

recognizes builders for their leadership in increasing energy efficiency, improving indoor air 

quality, and making homes zero energy ready.

The program traces its roots to the DOE Builder’s Challenge program, which was substantially 

revised and updated in early 2012 and renamed the DOE Challenge Home program. In summer 

2014 it was again renamed the Zero Energy Ready Home program. It builds upon the building 

science requirements of ENERGY STAR® Certified Homes, Version 3 and best practices tested 

by the Building America research and demonstration program. ZERH also incorporates the 

Environmental Protection Agency’s (EPA’s) Indoor airPLUS and WaterSense programs 

(EPA 2013a). 

DOE Zero Energy Ready Homes are verified by a qualified third party and are intended to be at 

least 40%–50% more energy efficient than a typical new home that was built to code minimum. 

This generally corresponds to a Home Energy Rating System (HERS) Index Score in the low- to 

mid-50s depending on the home’s size and location. The objective of the ZERH criteria is a set 

of building performance specifications that are so energy efficient that renewable power can 

cost-effectively offset most or all the annual energy consumption (DOE 2015).

The ZERH program is still in its infancy; market penetration is relatively slight and multifamily 

participation is negligible (Nebbia 2014). This is not unexpected at this early stage for a program 

that is a step above the more well-established ENERGY STAR New Homes program.

Potential barriers to achieving greater participation in the ZERH program include cost and 

constructability issues, which may differ based on climate region and building type. This report 

analyzes the cost, constructability, and energy implications of upgrading from ENERGY STAR 

to the ZERH specification for low-rise multifamily and attached housing units in climate zone 4.

DOE’s Building America research team Advanced Residential Integrated Energy Solutions 

Collaborative (ARIES) partnered with AvalonBay Communities (a large national property 

development, property management, and general contracting company) to develop a ZERH 

specification for a new low-rise multifamily development in New York State. AvalonBay owns 

and manages 82,576 housing units in 276 developments across the country. Each year the 

company builds numerous multifamily developments that it then operates as rental communities.

Each development typically contains 100–400 apartment homes, townhomes, or some 

combination. The company has built or is developing nearly 50 Leadership in Energy & 

Environmental Design- or ENERGY STAR-certified communities to date. The development that 

was analyzed in this case study is “Green III” in Elmhurst, New York, which is targeting 

ENERGY STAR certification and incentives through the New York State Energy Research and 

Development Authority (NYSERDA) Low-rise Residential New Construction Program. 
2

Figure 1. Avalon Green III under construction

The multifamily segment is becoming increasingly important in the new housing market. 

Nationally, multifamily units (those in buildings with five or more apartments) comprised 34% 

of new home permits in 2013—the highest percentage since 1985. Over the past 30 years, this 

segment has averaged 24% of residential permits; the growth to the present ratio occurred since 

the 2008 recession (Figure 2) (U.S. Census Bureau 2008).

Figure 2. New privately owned housing units authorized by

building permits in permit-issuing places—national

1.2 Zero Energy Ready Home Requirements

DOE ZERH certification requires the home to qualify for EPA’s ENERGY STAR label (Version 

3) and EPA’s Indoor airPLUS label. ENERGY STAR Version 3 requires insulation based on the 

2009 International Energy Conservation Code (IECC). However, the ZERH program requires 

0.0

250.0

500.0

750.0

1,000.0

2009 2010 2011 2012 2013

Permits

1 unit 2 to 4 units 5 or more units

63%

3%

34%
3

following the provisions of the 2012 IECC. The ZERH program includes provisions for energy 

efficiency, comfort, durability, and indoor air quality (DOE 2012). Basic requirements for ZERH 

certification are included in Table 1 (DOE 2014a).

Table 1. ZERH Requirements

Area Mandatory Requirements

ENERGY STAR 

for Homes Certified under ENERGY STAR Certified Homes Version 3

Envelope Fenestration meets or exceeds latest ENERGY STAR requirements

Ceiling, wall, floor, and slab insulation meets or exceeds 2012 IECC levels

Duct System Ducts located within the home’s thermal and air barrier boundary

Water Efficiency

Hot water delivery systems shall meet efficient design requirements 

(requires that the hot water distribution system stores no more than 0.5 gal 

of water in any piping/manifold between the hot water source and any hot 

water fixture)

Lighting and 

Appliances

All installed refrigerators, dishwashers, and clothes washers are

ENERGY STAR certified.

80% of lighting fixtures are ENERGY STAR certified or ENERGY STAR 

lamps (bulbs) in minimum 80% of sockets

All installed bathroom ventilation and ceiling fans are

ENERGY STAR certified.

Indoor airPLUS

Certified under EPA Indoor airPLUS – includes provisions relating to 

moisture control; pests; radon; heating, ventilating, and air conditioning 

(HVAC); combustion pollutants; water management; and materials 

emissions (EPA 2013a).

Renewable Ready

Consolidated Renewable Energy Ready Home Checklist completed. 

Preparations for future photovoltaics array are required only if the location 

has at least 5 kWh/m2/day average daily solar radiation, the roof is not 

shaded, and sufficient roof area is oriented within 45° of south

(DOE 2015).

1.2.1 Relevance to Building America’s Goals

By developing a prototype ZERH design for a typical multifamily development, this project 

addresses the following questions posed in the DOE Statement of Need (DOE 2014b):

• Can DOE Challenge [now ZERH] specifications be used by production builders to 

reliably deliver 30% homes to market [i.e., homes 30% more energy efficient than code]?

• How much more does a Challenge Home [now ZERH] cost to build compared with 

ENERGY STAR?
4

1.2.2 Research Questions

This research will address the following questions:

1. What set of measures can successfully result in meeting ZERH specifications for a 

market rate multifamily project in climate zone 4? 

2. What changes are required to upgrade a multifamily development from ENERGY STAR 

to ZERH? What design and construction approaches can help streamline the move to 

ZERH production?

3. What are the resulting costs to upgrade a multifamily development from ENERGY STAR 

to ZERH? Can any construction cost savings be captured if equipment needs are 

reduced? 

4. What are the energy impacts of upgrading a multifamily development from ENERGY 

STAR to ZERH? Is it cost-effective as calculated via Building Energy Optimization 

(BEoptTM) modeling?
5

2 Technical Approach

The ARIES team took the following approach to answer the questions:

1. Analyze current specifications: Obtain plans and specifications for a planned 

multifamily development, compare them to the ZERH criteria, and identify required 

changes.

2. Develop proposed modifications: Collaborate with the developer to modify the 

specifications to develop a ZERH specification for the multifamily development.

3. Estimate upgrade costs: Estimate the costs of the ZERH upgrades compared to the 

current specifications.

4. Energy modeling: Create models of the original designand an ENERGY STAR Version 

3 minimum and ZERH versions of representative housing units using BEopt (to evaluate 

annualized energy-related costs) and REM/Rate (to confirm ENERGY STAR and ZERH 

compliance). 

The subject test case is a three-building addition to an existing 444-unit, 21-building 

development in Elmsford, New York. The three new buildings include 68 units: two apartment 

buildings of 30 units each and one eight-unit townhome building. 
6

3 Analysis

3.1 Original Specifications

The original development was designed to comply with ENERGY STAR Version 3 plus specific 

requirements imposed by NYSERDA to receive incentives under its Low-rise Residential New 

Construction Program. The additional NYSERDA requirements included minimum 90 annual 

fuel utilization efficiency (AFUE) space- and water-heating efficiency, minimum seasonal 

energy efficiency ratio (SEER) 14.5 cooling, maximum air infiltration of 0.30 CFM50/ft2 of 

enclosure surface area, and common area lighting and enclosure requirements (NYSERDA 

2014). The original specifications and applicable ENERGY STAR Version 3 reference home 

specifications are shown in Table 2 for thermal envelope and Table 3 for equipment.

Table 2. ENERGY STAR Reference Design Compared to Original Specification—Thermal Envelope

Feature

ENERGY STAR 

Version 3 Reference 

Home

Original Design—

Apartments

Original Design—

Townhomes

Slab Floor R-10 perimeter,

2 ft deep

R-15 rigid foam on slab 

over garage

R-10 perimeter,

2 ft deep

Framed 

Floor R-30 grade 1 N/A

R-30 fiberglass batt 

grade 1 above garage 

and terrace

AboveGrade Walls

R-13 fiberglass batt + 

R-3 rigid 2 × 4 

exterior walls

R-15 fiberglass batt + 

R-3 rigid 2 × 4 exterior 

walls

R-15 FG batt + R-3 

rigid 2 × 4 exterior 

walls

Windows U: 0.32 SHGC: No 

requirement U: 0.32 SHGC: 0.40 U: 0.32 SHGC: 0.40

Doors No requirement No opaque exterior 

doors to apartments R-4.4

Ceiling R-38 grade 1 R-38 fiberglass batt 

grade 1

R-30 fiberglass batt 

grade 1

Infiltration 5 ACH50

Maximum 0.30 CFM50/ft2 of enclosure surface 

area per the NYSERDA Low-rise Residential 

New Construction Program
7

Table 3. Original Specification—Equipment

Feature ENERGY STAR

Version 3 Reference Home Original Specification

Space Heating 90 AFUE or ENERGY 

STAR certified

Forced air system; heat provided by hot 

water coil from tankless water heater –

96% AFUE

Space Cooling SEER 13 (NYSERDA 

requires SEER 14.5) 14.5 SEER split-system air conditioner

Water Heating 0.61 energy factor (EF) for 

instantaneous (tankless) 0.96 EF tankless water heater

Whole-House 

Ventilation

Designed and tested to 

ASHRAE 62.2

ENERGY STAR-certified bathroom 

exhaust fan—continuous operation to 

ASHRAE 62.2

Appliances ENERGY STAR certified ENERGY STAR certified

Lighting Minimum 80% ENERGY 

STAR certified

Minimum 80% ENERGY STAR 

certified

3.2 Zero Energy Ready Home Compliance

A home may comply with ZERH requirements through either the performance or the prescriptive 

path. The ZERH performance path requires that the thermal enclosure area-weighted average 

thermal conductivity, known as UA, meet the requirements of the 2012 IECC. When considering 

U values, a lower number results in less heat transfer, so the designed UA must be equal to or 

lower than the UA that would result from the prescriptive 2012 IECC insulation values (this is 

the “equivalent UA approach” (ICC 2012). UA values were calculated for one sample townhome 

(plan TC3) and one sample apartment (plan B4A). Both the apartment and townhome required a 

slight improvement in UA (Table 4). Table 4 also shows the UA for the ENERGY STAR 

Version 3 reference home.

Table 4. UA of Original Specifications Compared to ZERH

ENERGY STAR Version 

3 Reference Design (using 

prescriptive IECC 2009 

insulation values)

Original Design

ZERH (using 

prescriptive IECC 2012 

insulation values)

Apartment 205 202.8 197.8

Townhome 299 286.1 278.6

ZERH also contains mandatory requirements that are not required by ENERGY STAR. A 

summary as it pertains to this project is shown in Table 5 and Table 6. A number of upgrades, 

including pest prevention, duct protection, filtration, garage exhaust, preoccupancy flush, duct 

location, and domestic hot water (DHW) distribution system efficiency, were required to meet 

these mandatory requirements.
8

Table 5. Major ZERH Mandatory Requirements Compared to Original Design

Item Requirement Original Design 

Complies?

Duct Systems

Ducts located within home’s thermal and air 

barrier boundary or encapsulate with spray 

foam and cover with blow-in cellulose/

fiberglass (some exceptions allowable)

No (townhomes);

Yes (apartments)

Water 

Distribution 

Efficiency

The DHW distribution system shall store no 

more than 0.5 gal of water in any piping/

manifold between the hot water source and 

fixture. In the case of occupant-controlled or 

occupancy sensor-based recirculation systems, 

the storage limit is measured from the point 

where the branch feeding the fixture branches 

off the recirculation loop, to the fixture.

No

Appliances All installed refrigerators, dishwashers, and 

clothes washers are ENERGY STAR certified Yes

Renewable 

Ready Renewable Energy Ready Home checklist

Not applicable for this 

location due to insufficient 

solar radiation
9

Table 6. Major Indoor airPLUS Mandatory Requirements Compared to Original Design

Item Requirement Original Design 

Complies?

Moisture Control Hard surface flooring in kitchens, baths, entry, laundry and utility rooms, and piping 

in exterior walls insulated with pipe wrap Yes

Pests Corrosion-proof rodent/bird screenings installed at all openings that cannot be 

sealed (exception: dryer vents) No

HVAC Systems

Duct systems protected from construction debris and no building cavities used as 

supplies or returns No

No air-handling equipment or ductwork installed in garage and continuous air 

barrier in adjacent assemblies Yes

Central forced air systems have minimum efficiency reporting value (MERV) 8 and 

no ozone generators in home No

Carbon monoxide alarms installed in each sleeping zone (e.g. common hallway) 

according to National Fire Protection Association 720 Yes

Multifamily buildings: Smoking restrictions implemented and Environmental 

Tobacco Smoke transfer pathways limited Yes

Townhomes: Door closer installed on all connecting doors; in homes with exhaustonly whole-house ventilation (e.g., bath fans), either a 70-CFM exhaust fan installed 

in the garage or pressure test conducted to verify the effectiveness of the garage-tohouse air barrier

No

Materials

Certified low-formaldehyde composite wood materials and structural plywood and 

oriented strand board PS1 or PS2 compliant Yes

Certified low- or no-volatile organic compound interior paints and finishes used Yes

Carpet, carpet adhesives Carpet and Rug Institute Green Label Plus and carpet 

cushion Carpet and Rug Institute Green Label Yes

Final Inspection HVAC system and ductwork verified to be dry and clean and new filter installed No

Home ventilated before occupancy No
10

3.3 Design Changes

3.3.1 Thermal Envelope

The ZERH design required an approximately 2%–3% reduction in UA. This could be achieved 

by improvements to any exterior surfaces—walls, slab/floors, ceiling/roof, or windows. 

Improvements to the ceiling/roof or floor/slab would not have affected lower and upper floor 

apartments, respectively, and the amount of additional insulation would not have been practical 

in all cases given the planned structure. Improvement to the window U-value would have forced 

the windows into another cost category and required using a different supplier, which was 

undesirable for the builder. Improvements to the walls were determined to be the most practical. 

The planned exterior wall construction was R-15 fiberglass batts in a 2 × 4 wall cavity plus R-3 

rigid exterior insulation. Upgrading the exterior rigid insulation to R-6 would provide the 

necessary improvement (Table 7). 

Table 7. Improvement to Whole-Envelope UA with Added Exterior Rigid Insulation

Original Design UA 

(R-3 insulating 

sheathing)

Original Design UA 

with R-6 Insulating 

Sheathing

Target UA for ZERH 

Compliance (using 

prescriptive IECC 2012 

insulation values)

Apartment 202.8 195.1 197.8

Townhome 286.1 272.6 278.6

3.3.2 Domestic Hot Water Distribution Efficiency

Neither sample unit complies with the ZERH DHW distribution efficiency requirements as 

originally designed; both have pipe runs that exceed the 0.5-gal storage limit from the water 

heater to the farthest fixture. 

Compliance could be achieved by adding an on-demand hot water recirculation system with 

occupancy sensors that activate the hot water when the occupant enters the room. This could be 

considered where moving the heater is not practical; however, the team decided to explore 

reducing the pipe water volume.

Reducing all DHW pipe runs to no more than 0.5 gal would require some combination of 

reduced pipe diameters (perhaps in conjunction with the use of a plumbing manifold system to 

maintain adequate flows) and/or plan revisions to bring the end fixtures and water heater closer 

together. The smallest impact on the designs would be to move the water heater to a more central 

location in the floor plan—ideally in a closet or service space. Typically the water heater (which 

also provides space heating via a hot water loop to the air handling unit) is located adjacent to an 

outside wall to minimize vent pipe length. Moving the water heater to a more central location 

would have the additional benefit of moving it closer to the air handling unit to reduce heat loop 

pipe runs and associated heat losses. Figure 3 and Figure 4 show the original and proposed 

locations of the water heaters in relationship to end-use fixtures and the air handling unit for the 

sample apartment and townhome, respectively. Table 8 quantifies the change in pipe and vent 

run distances that resulted from the relocation and the associated first costs (about $68 for the 

apartment and $110 for the townhome). Pipe length from the water heater to the fixtures would 

be decreased; however, the combustion vent length would increase (a 1⁄4-in./ft pitch to the outside 
11 

would be maintained). The length of the cold water main line may change to reach the new 

location; the gas regulator vent would have to be extended to the outside.

Figure 3. Two-bedroom apartment—water heater relocation

Figure 4. Two-bedroom townhome—water heater relocation
12

Table 8. Change in Vent and Heat Loop Piping Distance (in feet) and Cost Implications

Original Modified Difference Pipe Cost 

Difference 

($) Vent Heat 

Loop

DHW 

Pipe Vent Heat Loop

DHW 

Pipe Vent Heat Loop

DHW 

Pipe

Apartment 1 29 82 17 12 74 +16 –13 –8 +$67.95

Townhome 5 39 103 35 5 72 +30 –34 –31 +$110.20

Vent material cost: $4/ft. 

Heat loop and DHW pipe: $0.21/ft. of 1⁄2-in. diameter; $0.38/ft of 3⁄4-in. diameter; $1.10/ft of 1-in. diameter.

Regulator vent line (3/8-in. copper): $1/ft. 

The water heater can be moved from an exterior location to an interior closet with a sealed 

combustion/condensing heater, however, certain precautions are advisable. According to the 

2010 New York Plumbing Code any water heater that uses a solid or gas as a fuel cannot be 

installed within a bathroom, bedroom, or in a bedroom closet for which the only access is via a 

bedroom or bathroom. Only direct-vented water heaters are exceptions (ICC 2007). Other best 

practices include weather-stripping the door to the living space to prevent any combustion 

byproducts from infiltrating the living space and using fire-retardant cement backerboard in the 

closet. The local code official will have the final say about the permissibility of the new location.

The National Renewable Energy Laboratory’s DHW Draw Profile Generation tool is an Excel 

spreadsheet-based DHW event generator2 that can be used to simulate hot water draw events 

(Hendron et al. 2010). It can generate annual DHW use data with resolution from a 1-second to a 

6-minute time step and account for incoming cold water temperature variations by climate.

The tool was used to estimate the impact on water and energy consumption of the DWH 

distribution system redesign in response to the need to comply with ZERH criteria. LaGuardia, 

New York, climate data were used to generate an annual draw profile for a two-bedroom and a 

three-bedroom unit. The annual number of draws by fixture (or group of nearby fixtures, here 

termed a zone [Table 9]) was summed. Draws that occurred less than 10 minutes after a draw by 

the same fixture (or a fixture within the same zone) were eliminated, because the water was 

assumed to be still warm enough for use. The 10-minute threshold was determined by calculating 

the time for 125°F water to cool to 105°F in uninsulated .075-in.-diameter cross-linked 

polyethylene (PEX) pipe (see Appendix A for calculation details). Also, draws of shorter 

duration than the time the water would take to travel from the water heater to the primary fixture 

(assuming maximum flow rate for the respective fixture type per federal standards and the 

respective pipe diameter) were not counted, because full service temperature was assumed to be 

unnecessary for these draws. The dishwasher and washing machine draws were not counted, 

because ZERH does not impose this requirement on appliances (they do not typically wait for, 

and therefore waste, hot water); however, draws from these appliances were considered in the 

10-minute wait time (i.e., draws from fixtures in the same zones as these appliances were not 

counted if they followed them by less than 10 minutes).

 2 The DHW draw generator may be found at 

https://buildingsfieldtest.nrel.gov/domestic_hot_water_dhw_draw_profile_generation
13

Table 9. Apartment DHW Zones

Zone Fixtures

1 Kitchen sink, dishwasher

2 Master bathtub, master bath lavatories, master bath shower

3 Bathroom 2 bathtub, bathroom 2 shower, bathroom 2 lavatory, 

washing machine

4 Wet bar

Summing the resulting number of counted draws for the year for each hot water fixture zone and 

multiplying each by the pipe volume from the water heater to the fixture and by the ratio of hot 

to cold water as predicted by the draw calculator results in the annual water wasted while waiting 

for hot water. To calculate the energy in this wasted hot water, a temperature rise was determined 

for each draw based on the difference between the average incoming cold water temperature 

(from the National Renewable Energy Laboratory’s draw generator) and the 125°F supply 

temperature, and the efficiency of the water heater (0.96 EF). See Appendix A for the draw 

profile, associated assumptions, and energy calculations. The results of the calculations are 

provided in Table 10 and Table 12. 

Table 10. Apartment DHW Distribution Water and Energy Waste per Year

Zone

Counted 

Draws

Original Location ZERH Location

Water 

Savings

(gal)

Site Energy 

Savings

Pipe 

(kBtu)

Volume 

(gal)

Water 

Waste 

(gal)

Energy 

Waste 

(kBtu)

Pipe 

Volume 

(gal)

Water 

Waste 

(gal)

Energy 

Waste 

(kBtu)

1 2,773 0.54 1,118 643 0.44 896 515 291 128

2 788 1.08 342 197 0.48 204 117 331 79

3 447 0.66 280 160 0.33 137 78.7 190 82

4 535 0.66 448 257 0.22 191 109 230 148

Totals 4543 2,188 1,258 1,428 820 1,042 437

The original plumbing layout for the townhome included a long run of 1-in. diameter DHW pipe 

from the water heater through the unit to the center of the first floor, where it then divided into 

smaller branch lines. Because most of the DHW was in this common trunk line a simplifying and 

conservative (in the sense of estimating savings) assumption was made to group all fixtures into 

one zone for the original energy/water waste calculations; i.e., any draw from any fixture was 

considered to recharge the entire system. Therefore Table 11 and Table 12 show a single zone 

for the original location, and three zones for the compliant location. This results in slightly fewer 

counted draws for the original configuration than the ZERH location, because no draw that 

follows another draw by less than 10 minutes for any fixture in the townhome is counted.
14

Table 11. Townhome DHW Zones (ZERH version)

Zone Fixtures

1 Kitchen sink, dishwasher, master bathtub, master bath sink, master bath shower

2 Powder room sink, clothes washer

3 Bathroom 2 bathtub, bathroom 2 shower, bathroom 2 sink

Table 12. Townhome DHW Distribution Water and Energy Waste per Year

Zone

Counted 

Draws

Original Location Compliant Location

Water 

Savings

(gal)

Site 

Energy 

Savings

(kBtu)

Pipe 

volume 

(gal)

Water 

Waste 

(gal)

Energy 

Waste 

(kBtu)

Pipe 

Volume 

(gal)

Water 

Waste 

(gal)

Energy 

Waste 

(kBtu)

All 

(original 

design)

2,187 1.8 1,212 697 N/A N/A N/A

1 2,123 N/A N/A N/A 0.48 497 286

2 294 N/A N/A N/A 0.28 72 41

3 362 N/A N/A N/A 0.17 109 63

Totals 1,212 697 678 390 652 307

The annual energy and water savings that accrue from the water heater relocation is estimated to 

be 436 kBtu (5%) and 1,042 gal for the apartment and 307 kBtu (3%) and 652 gal for the townhome. If a recirculating system were used instead, the water and energy savings would differ.

This is a rough estimate, because the zoning of fixtures is imperfect and temperatures are 

idealized. Also, DHW radiative heat loss within the conditioned space contributes to space 

heating and exacerbates cooling loads. These interactive effects are not considered here but can 

be significant (they have been estimated at 20%–40% of DHW distribution energy savings for 

multifamily recirculating systems using pump controls (Dentz et al. 2015)). Despite these 

limitations, this is a reasonable range of energy and water savings from the ZERH DHW 

distribution efficiency requirement for these homes.

3.3.3 Ducts in Conditioned Space

A home must meet the following conditions to comply with ZERH: 

• No more than 10 ft of forced-air ducts may be outside the thermal and air barrier 

boundary, unless 

o The ducts are in an unvented attic (even if not conditioned with a supply register) 

or 

o For climate zone 4A ducts in a vented attic have a minimum R-8 duct insulation 

plus a minimum 1.5 in. of closed-cell spray foam insulation encapsulating the 

ducts and 
15

o the ducts are buried under at least 2 in. of blown-in attic insulation and 

o Total duct leakage is no more than 3 CFM25/100 ft2 of conditioned floor area. 

• In all cases the HVAC equipment must still be located within the home’s thermal and air 

barrier boundary. 

The ductwork for the apartment units was designed wholly within the conditioned space; the flat 

roofs enclose an unvented attic cavity with a dropped ceiling below. However, part of the duct 

system in the townhome passes through the unconditioned vented attic. 

The team determined that most practical approach to complying with these criteria in the 

townhome would be to bring the ducts into a furred-down soffit under the ceiling, rather than 

bringing in an additional subcontractor to apply the spray foam and relying on the lower duct 

leakage. This would require a soffit in the second-floor center hallway and master bedroom 

closet (Figure 5). The soffit framing cost was estimated at $100 extra per townhome, but the 

reduced ductwork was estimated to save $82.50; these costs are relatively low because of the 

high material volumes and production nature of the construction. 

Figure 5 is a conceptual schematic of the revised duct design—registers would need to be 

designed and located for proper air throw into the room and to avoid short-circuiting to return air 

pathways. Note that moving the supply registers away from their original location on the exterior 

walls above windows and to the interior walls could create comfort issues. As cold air infiltrates 

near window openings, occupants may feel a difference in temperature across the room. 

Improved envelope insulation and airtightness would be required to mitigate this issue. Other 

Building America teams have written extensively about compact air distribution systems

(Burdick 2013). 

Figure 5. Townhome unit ductwork—revisions in red
16

3.3.4 Garage Exhaust Fan

Because the townhomes have attached garages and use exhaust-only ventilation, provisions must 

be made to prevent contaminants in the garage from entering the home. This could be 

accomplished by equipping the garage with an exhaust fan vented directly outdoors with a 

minimum installed capacity of 70 CFM at an installed cost of $120 per fan. The fan can be wired 

for continuous operation or with automatic controls such as a motion detector that activates the 

fan whenever the garage is occupied and operates for at least 1 hour after the garage has been 

vacated. 

Alternatively, the garage-to-house air barrier can be tested for integrity. The test requires the 

garage (with all openings closed) to maintain a pressure difference greater than 45 Pascals with 

the home while the home maintains a 50 Pascal pressure difference with respect to the outdoors

(EPA 2013b).

The simplest and most reliable compliance option chosen for this analysis was a continuously 

operating exhaust fan. Although a verified garage-to-house air barrier would be preferable, it 

could not be guaranteed before construction; the additional cost to retrofit the fan 

postconstruction if the air barrier failed would be considerably higher than installing it at the 

start.

3.3.5 Equipment Sizing Reduction

The revised design peak heating and cooling loads as calculated with BEopt are about 25% lower 

than the original design for the townhome and about 10% lower for the apartment. Under 

ENERGY STAR Version 3, listed total cooling capacity must be 95%–115% of design total heat 

gain or next nominal size (generally in 0.5-ton increments for single-speed equipment). For 

warm air heating systems, the output capacity must be 100%–140% of calculated system load (or 

next nominal size), unless a larger size is dictated by the cooling equipment selection (EPA 

2013b). The ENERGY STAR-compliant townhome cooling equipment could be downsized from 

3 to 2.5 tons; heating equipment could be reduced effectively to the next smaller nominal 

equipment size as well, a 32 kBtu/h unit, to meet ZERH requirements (Table 13).

Table 13. Space-Conditioning Equipment Sizing Reduction

Heating 

(kBtu/h)

Cooling 

(tons)

Apartment

Original load 22.3 1.7

Original specified capacity 27.1 2

ZERH load 21.7 1.6

ZERH specified capacity 27.1 2

Capacity reduction 0 0

Townhome

Original load 36.2 2.69

Original specified capacity (next closest size) 57.4 3

ZERH load 28.5 2.01

ZERH specified capacity 32.4 2.5

Capacity reduction 25 0.5
17

3.3.6 Summary of Design Changes

The following table (Table 14) summarizes the design changes needed to comply with ZERH:

Table 14. Design Changes

Item Change

UA—Exterior Walls

Change from R-3 exterior rigid insulation to R-6 exterior rigid 

insulation. This change drives reductions in heating and cooling 

equipment sizing.

Domestic Water 

Heating Distribution 

Efficiency

Move water heaters to central location—increase vent length; 

decrease pipe length

Duct Protection Cover duct openings during construction and vacuum out ducts 

thoroughly before installing registers, grilles, and diffusers

Air Distribution 

System Design

Bring ducts into conditioned space by installing soffit in townhome 

second floor and installing a trunk duct down the center of the unit 

with short branch ducts to each room. Registers would be located in 

the interior walls rather than the sidewall.

Change from MERV 6 to MERV 8 filters for all air handling units

Attached Garages Install 70 CFM fan vented to outdoors

Pest Control Add rodent- and corrosion-proof screens to exhaust fans and 

combustion vent
18

4 Modeling

BEopt version 2.2.0.2 was used to create energy models of the original design, the ZERHcompliant, and a minimum ENERGY STAR-compliant version of the apartment and townhome 

to estimate source energy savings and evaluate annualized energy-related costs. Costs to upgrade 

from the original design to ZERH were obtained from subcontractors and estimates by the 

developer (Table 15). The BEopt cost database was used for costs of ENERGY STAR Version 3 

minimum specifications (Table 16). The costs in Table 16 would be added to those in Table 15 if 

using ENERGY STAR Version 3 minimum as the baseline.

Table 15. Incremental Costs—Original Design to ZERH

Item Design Change Incremental Cost/Savings

Exterior 

Walls

1-in. R-3 to 1.5-in. R-6 insulated 

sheathing

$1.04/ft2 exterior wall area, resulting in a 

$894 cost increase for the apartment and 

$1,284 increase for the townhome.

Domestic 

Water 

Heating

Relocated water heater—polyvinyl 

chloride pipe extension for both 

intake and exhaust; reduced water 

pipe and heat loop pipe lengths

$4/lf of length from outside wall plus $50 

labor per apartment. Saving from reduced 

heat loop and DHW pipe: $0.21/lf of 1⁄2 in.; 

$0.38/lf of .075 in.; $1.10/lf of 1 in. Net 

cost of $68/apartment and $110/townhome.

Duct 

Protection

Cover duct openings during 

construction and vacuum out ducts 

on completion

2 hours total per unit at $22/h = $44/unit

Air

Distribution 

System 

Design

Soffit in the townhome top floor. 

Trunk down center of apartment 

with registers in center rather than 

near sidewall

$100/townhome for additional framing; 

$82.50 savings for reduced ductwork 

($2.20/lf for 8-in. flex duct and $11/lf for 

12-in. × 12-in. fiberboard trunk duct); 

resulting in a negligible net increase of 

$17.50.

MERV 6 to MERV 8 filters for all 

air handling units $3 additional per filter

Attached 

Garages 70 CFM fan and labor $120 for townhomes only

Pest 

Control

Rodent- and corrosion-proof 

screens to exhaust fans and 

combustion vent

$5/vent or $20/apartment and 

$25/townhome

Equipment 

Size

Townhome air conditioner and 

heating coil downsize

$100 reduced cost for 3 to 2.5 ton air 

conditioner and $200 reduced cost for 57.4 

to 32.4 kBtu/h
19

Table 16. Additional Incremental Costs—ENERGY STAR Version 3 Baseline to ZERH

Item

ENERGY STAR 

Version 3 

Minimum

ZERH Incremental Costs

Cavity Insulation R-13 R-15 $0.06/ft2 exterior wall

Cooling Equipment SEER 13

SEER 14.5 

(NYSERDA 

requirement)

$123/unit

Space- and WaterHeating Equipment

0.92 EF tankless 

water heater

0.96 EF tankless 

water heater $67/unit

Projected annual source energy consumption was reduced by about 2% for the apartment and 8% 

for the townhome (Figure 6 and Figure 7) when comparing the original to the ZERH designs. 

This reduction is small because the original design was already superior to minimum ENERGY 

STAR requirements—by 8% for both the apartment and townhome—primarily due to the 

minimum space heating equipment efficiency requirement of 90 AFUE imposed by NYSERDA. 

Many of the additional ZERH design changes related to indoor air quality (and one for pest 

protection). The reduction in energy use from the as-built design was due to the upgrade in 

exterior rigid insulation from R-3 to R-6, relocation of the DHW heater and relocating ducting 

into conditioned space in the townhome. Adding garage ventilation in the townhome increased 

energy use there. The DHW distribution energy savings was factored into BEopt by adjusting the 

hot water fixture use fraction from 1.0 to 0.95 for the apartment and to 0.97 for the townhome.

Figure 6. Apartment source energy use from BEopt

0

10

20

30

40

50

60

70

80

90

100

ENERGY STAR V3

Minimum

Original Design ZERH

Source Energy Use (MBtu/year)

House Configuration

Source Energy Use - Apartment - 2 bedroom

Misc. (G)

Lg. Appl. (G)

Hot Water (G)

Heating (G)

Cooling (E)

HVAC Fan/Pump (E)

Lights (E)

Lg. Appl. (E)

Vent Fan (E)

Misc. (E)
20

Figure 7. Townhome source energy use from BEopt

In Figure 8 and Figure 9, the source energy savings compared to a baseline home (2009 IECC) 

and the annualized energy-related costs of three design specifications are presented: ENERGY 

STAR Version 3 minimum, the original design, and ZERH. The annualized energy-related costs 

account for the utility bill savings and the incremental construction costs associated with the 

upgrades. All the additional costs, including the non-energy-related upgrade costs required by 

ZERH were factored into this analysis. For the apartment, the BEopt annualized energy-related 

costs for the ZERH design are lower than the ENERGY STAR minimum and original design by 

$2 and $12, respectively. For the townhome the BEopt annualized energy-related costs for the 

ZERH design are lower than the ENERGY STAR minimum and original design by $79 and 

$134, respectively. For the apartment, adjusted source energy savings increased by 3.2% and 

1.4% for the ZERH compared to the ENERGY STAR minimum and original design, 

respectively. For the townhome, adjusted source energy savings increased by 9.5% and 5.8% for 

the ZERH compared to the ENERGY STAR minimum and original design, respectively. Utility 

rates used are shown in Table 17.

0

20

40

60

80

100

120

140

160

ENERGY STAR V3

Minimum

Original Design ZERH

Source Energy Use (MBtu/year)

House Configuration

Source Energy Use - Townhome - 3 bedroom

Misc. (G)

Lg. Appl. (G)

Hot Water (G)

Heating (G)

Cooling (E)

HVAC

Fan/Pump (E)

Lights (E)

Lg. Appl. (E)

Vent Fan (E)

Misc. (E)
21 

Figure 8. Apartment (single unit B4) annualized energy-related costs from BEopt

 

Figure 9. Townhome (single unit TC3) annualized energy-related costs from BEopt

BEopt Reference Home

2009 IECC

BEopt Reference Home

2009 IECC 

ENERGY STAR 

V3 minimum 

Original Design

ZERH

ENERGY STAR 

V3 minimum 

Original Design

ZERH
22

Table 17. Utility Rates

Utility Rate

Electricity $8/month + $0.13/kWh

Natural gas $8/month + $1.10/therm

The impact on the renters’ utility bills is shown in Table 18. In this case the savings accrue to the 

renters, not to the developer that incurred the additional costs. The projected HERS indices for 

the units are shown in Table 19.

Table 18. Projected Annual Utility Bill Savings for the Original and ZERH Designs

Utility Bill Savings for 

Original Design Compared to 

ENERGY STAR Version 3 

Minimum

Utility Bill Savings for ZERH 

Compared to ENERGY STAR 

Version 3 Minimum

Apartment $24 $41

Townhome $67 $164

Table 19. HERS Indices for Original and ZERH Designs

ENERGY STAR Version 3 

Minimum

Original 

Design ZERH

Apartment 71 58 58

Townhome 71 56 52
23

5 Results and Discussion

5.1 Cost-Effectiveness

One purpose of this analysis was to document the costs necessary to step up from the original 

design, which was compliant with ENERGY STAR Version 3, to ZERH for multifamily builder. 

Cost determines to a large extent the feasibility of implementing ZERH for this market segment. 

The overall costs to upgrade from the original design to ZERH are shown in Table 20. This 

development was only 68 units because it was an addition to a larger development. Therefore, 

the total project incremental costs were modest. Typical new developments range from 200 to 

400 units, so total additional costs could be hundreds of thousands of dollars in those cases. The 

incremental costs to upgrade from a hypothetical ENERGY STAR Version 3 minimum design to 

ZERH are shown in Table 21.

Table 20. Total Incremental Costs from Original Design to ZERH

Cost per Square 

Foot Floor Area

Cost for 

Sample Unit Cost per Buildinga

Apartment (B4) $0.77 $1,029 $17,506 (x2 buildings)

Townhome (TC3) $0.72 $1,304 $6,723

Total project $41,735 a Extrapolates exterior insulation costs per foot to entire building envelope; assumes all other incremental costs are 

equal for all apartments. 

Table 21. Total Incremental Costs from ENERGY STAR Version 3 Minimum Design to ZERH

Cost per Square

Foot Floor Area

Cost for 

Sample Unit Cost per Buildinga

Apartment (B4) $1.08 $1,444 $28,484 (x2 

buildings)

Townhome (TC3) $1.28 $2,319 $14,630

Total project $71,598 a Extrapolates exterior insulation costs per foot to entire building envelope; assumes all other incremental costs are 

equal for all apartments. 

The residents pay for all utilities in these rental apartments, so the savings would accrue to the 

residents; the construction costs would be borne by the developer. The developer would be 

motivated to make these improvements only if they increased marketability, raised rents, 

increased occupant satisfaction, or reduced maintenance costs. These factors are discussed in 

Section 5.2. 

5.2 Impacts and Trade-Offs

Of the seven upgrades required to comply with the ZERH requirements, four have energy 

impacts (one of which increases energy use), three relate to indoor environmental quality, and 

one to pests. The DHW distribution efficiency requirement reduces energy waste but also 

improves performance in the form of less wait time for hot water and reduced water waste. A 

discussion of other impacts of the changes is provided in Table 22.
24

Table 22. Impacts and Trade-Offs for Each Design Change

Item Improvement Area Impact/Trade-Off/Risk

Added Exterior 

Wall Insulation Energy

Improved wall performance in terms of comfort because interior surface temperatures will be 

higher in heating season. Although R-3 is sufficient to meet the International Residential Code 

requirements for insulated sheathing in zone 4 as indicated in Table R702.7.1 (ICC n.d.), R-6 

will provide added protection against moisture risks due to condensation within the wall. Vinyl 

siding attachment would not be adversely affected by the one inch insulation thickness, but 

greater thicknesses required in colder climates or heavier siding types may require longer 

fasteners or closer fastener spacing. Adhesively applied stone veneer may also be complicated 

by thicker exterior insulation, and concrete slab floors with exposed slab edges would require 

alternative details.

DHW 

Distribution 

Efficiency

Energy, DHW 

performance

This change will reduce wait time for hot water at most fixtures, reduce water heating energy, 

and save water. The smaller heat loop distance may also improve space heating efficiency. The 

plan change does eliminate an interior closet in exchange for a larger closet on the porch. 

Locating the water heater inside the apartment may complicate water heater maintenance, which 

previously would be done from an exterior porch rather than inside the apartment.

Duct Protection Indoor environmental 

quality

Preventing dust from entering the air distribution system and cleaning any that does enter is 

beneficial for indoor air quality, equipment operation, and filter longevity.

Ducts into 

Conditioned 

Space

Energy

This is an energy benefit. The reduced ceiling height in the townhome’s second-floor hallway 

and closet is a drawback of this design change. If windows are not upgraded to reduce 

infiltration and radiative heat loss, drafts and discomfort from windows that are no longer 

washed with conditioned air could cause residents to adjust thermostats upward in winter and 

downward in summer, offsetting some energy savings.

Filter Upgrade 

from

MERV 6 to 8

Indoor environmental 

quality

Air quality should be enhanced by the higher MERV filter. Some additional fan energy may be 

required to push air through the MERV 8 filter.

Attached 

Garage Exhaust 

Fan

Indoor environmental 

quality

The reduced risk of garage pollutants entering the home comes at a cost of additional fan energy 

required by the garage exhaust fan and additional maintenance for the fan. Because the fan is 

fairly quiet and located in the garage, it may not be noticed if it fails.

Pest Control 

Screens Pests Anticipated risks or trade-offs to installing these screens are minimal. However, they can 

become clogged by dust and debris depending on airflow. Regular cleaning may be necessary.
25

6 Conclusions

Four research questions were addressed by this analysis:

1. What set of measures can successfully result in meeting DOE ZERH specifications for a 

market-rate multifamily project in climate zone 4? 

The primary energy measures that achieve compliance with ZERH exceed ENERGY STAR 

Version 3 only slightly. The units analyzed complied with R-10 slab edge insulation, R-30 floor 

insulation (or R-15 over podium slab), R-15 wall cavity insulation, R-6 insulating sheathing, U0.32 windows, R-30 and R-38 ceilings, 96% efficiency water and space heating, and 13 SEER 

cooling. 

2. What changes are required to upgrade a multifamily development from ENERGY STAR 

to ZERH? What design and construction approaches can help streamline the move to 

ZERH production?

For the units in the sample project analyzed, relatively few items (seven) would need to be 

modified from the original design. The modifications are:

• Increase the exterior rigid insulation thickness from 1⁄2 in. to 1 in. 

• Relocate the water heaters. 

• Bring the ducts into a dropped soffit in townhome units. 

• Upgrade to MERV 8 filters. 

• Add rodent screens to vents. 

• Protect and clean ducts. 

• Install an exhaust fan in the garage of each townhome unit. 

All these design upgrades could have been incorporated relatively easily any time before 

construction; however, the DHW distribution and duct location changes would optimally be 

made during the design phase. The design changes (dropped soffit for townhome ducts and using 

closet space for water heaters) would be a major drawback for some developers—alternatives 

that have a lower design impact may be necessary.

If the development was starting at a baseline of ENERGY STAR Version 3 minimum, the 

following additional upgrades would be required: 

• Increase cavity insulation from R-13 to R-15. 

• Increase space and DHW heating tankless unit efficiency from 0.92 EF to 0.96 EF. 

• For NYSERDA incentives, increase the air-conditioner condenser efficiency from SEER 

13 to SEER 14.5.

3. What are the resulting costs to upgrade a multifamily development from ENERGY STAR 

to ZERH? Can any construction cost savings be captured as a result of reduced 

equipment needs?
26

The net costs to upgrade to ZERH are approximately $1,029 and $1,304 for a typical apartment 

and townhome, respectively. Extrapolating this to all three buildings would result in an 

approximately $42,000 increase in construction cost for all 68 units, or $0.57/ft2

. The full added 

costs were higher but savings from reduced piping and ductwork and equipment downsizing 

offset some of those costs. 

If the development was starting at a baseline of ENERGY STAR minimum, the net costs to 

upgrade to ZERH would be approximately $1,444 and $2,319 for a typical apartment and 

townhome, respectively. Extrapolating this to all 68 units would result in an overall upgrade cost 

of approximately $79,000 or about $1.09/ft2. Again, the fully added costs were higher but 

savings from equipment downsizing and reduced domestic hot water piping and ductwork offset 

these costs.

4. What are the energy impacts of upgrading a multifamily development from ENERGY 

STAR to ZERH? Is it cost-effective as calculated via BEopt modeling?

Upgrading from the original ENERGY STAR design to ZERH resulted in a projected 2%–8% 

reduction of source energy consumption, or 1.9–10.4 MBtu/year. This number is modest, in part 

because the original design was already 8% better than the ENERGY STAR minimum 

requirements in terms of source energy consumption. Annualized energy-related costs of the 

ZERH design were approximately $12 lower for the apartment and approximately $134 lower 

for the townhome compared to the original design.
27

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29

Appendix

Domestic Hot Water Distribution Waste Calculation 

Assumptions:

• Ignore draws of shorter duration than water flow time from the water heater to the 

highest-use fixture in the zone.

• Ignore draws less than 10 min after previous draw from the same fixture or fixture in 

same zone (based on pipe heat loss calculations from 125°F to 105°F in 0.75-in. pipe).

• Base waste on the counted number of qualifying events per fixture.

• Climate location: New York, LaGuardia.

• Tank temperature 125°F (DHW draw generator default value).

• Draw temperature 110°F (DHW draw generator default value).

• Wasted water is equivalent to the pipe volume from the water heater to the highest-use 

fixture in the zone.

• Wasted energy is equivalent to the Btu embedded in the wasted water volume, assuming 

temperature rise from mains water temperature (56°F) to 125°F divided by water heater 

efficiency (96%).

• Estimations of pipe volume from water heater to highest use fixture for purposes of 

estimating DHW waste assumes .075-in. diameter throughout.

Pipe Heat Loss Calculation 

Steady-state heat loss equation (University of British Columbia n.d.): θtarget = θenvironmental + 

(θ0 - θenvironmental)* e -kt

Where:

θenvironmental is wall cavity temperature (70°F)

θ0 is original water temperature (125°F)

θtarget is target water temperature (105°F)

After inputting known variables and solving for t, the time for water to cool from 125°F to 105°F 

is approximately 10 min.
30

Table 23. Inputs and Results—DHW Distribution Waste—Apartment

Zone 1 2 3 4

Fixtures in zone

Kitchen 

sink

dishwasher

M bathtub

M bath 

lavatories

M bath 

shower

Bath 2 

bathtub

bath 2 shower

bath 2 

lavatory

washing 

machine

Wet 

bar

Limit (min) based on heat loss calc .075-

in. uninsulated PEX 125 tank temp to 

105 useful temp

10 10 10 10

Duration minimum (seconds). Draws 

shorter than this will not yield hot water 

so hot water is presumably not needed 

(assume ZERH location has same 

duration limit as original location)

15.6 30.8 24.5 22.2

Counted draws 2,773 788 447 535

Average counted draws per day 7.60 2.16 1.22 1.47

Pipe length to highest-use fixture—

original case (kitchen sink) (ft) 20.6 40.7 32.4 29.3

Pipe length to highest-use fixture—

ZERH case (kitchen sink) (ft) 16.5 24.3 15.8 12.5

Pipe volume to highest-use fixture—

original case (kitchen sink) (gal); 

assumes 0.75-in. pipe

0.53 1.04 0.83 0.75

Pipe volume to highest-use fixture—

ZERH case (kitchen sink) (gal); assumes 

0.75-in. pipe

0.42 0.62 0.4 0.32

Total DHW waste—hot only (gal) 896 342 280 448

Total DHW use—hot only (gal) 5,381 7,764 515 2,792

% waste DHW 16.6% 4.4% 54.3% 16%

Total water use from hot water taps 

(gal) (includes cold water used to 

temper DHW at tap)

6,673 9,849 681 3,064

Total water waste (gal) from hot water 

taps 1,169 820 370 401

Flow rate highest-use fixture (gal/min 

based on federal standards)

(EPA 2014)

2.2 2.2 2.2 2.2

Pipe diameter to highest-use fixture (in.) 0.75 0.75 0.75 0.75

Flow speed highest-use fixture (ft/s) 

(TLV, Inc. 2015) 1.32 1.32 1.32 1.32
31

Table 24. Inputs and Results—DHW Distribution Waste—Townhome

Original ZERH

Fixtures in zone All 1 2 3

Limit (min) based on heat loss 

calculation .075-in. uninsulated PEX 

125 tank temperature to 105 useful 

temperature

All

Kitchen sink

Dishwasher

M bathtub

M bath sink

M bath shower

Powder

room 

sink

clothes 

washer

Bath 2 

bathtub

Bath 2 

shower

Bath 2 

Sink

Duration minimum (seconds). Shorter 

draws will not yield hot water so hot 

water is presumably not needed 

(assume ZERH location has same 

duration limit as original location)

10 10 10 10

Counted draws 43.3 43.3 43.3 4303

Average counted draws per day 2,187 2,123 294 362

Pipe length to highest-use fixture—

original case (kitchen sink) (ft) 5.99 5.82 0.81 0.99

Pipe length to highest-use fixture—

ZERH case (kitchen sink) (ft) 57.2 N/A N/A N/A

Pipe volume to highest-use fixture—

original case (kitchen sink) (gal); 

assumes 0.75-in. pipe

N/A 18.9 11.1 17.5

Pipe volume to highest-use fixture—

ZERH case (kitchen sink) (gal); 

assumes 0.75-in. pipe

1.46 N/A N/A N/A

Total DHW waste—hot only (gal) N/A 0.48 0.28 0.45

Total DHW use—hot only (gal) 1,212 497 72 109

% waste DHW 17,961 12,828 3,831 2,752

Total water use from hot water taps 

(gal) (includes cold water used to 

temper DHW at tap)

7% 4% 2% 4%

Total water waste (gal) from hot water 

taps 25,078 18,248 4,102 4,105

Flow rate highest-use fixture (gal/min 

based on federal standards) (EPA 

2014)

3,195 1,027 83 162

Pipe diameter to highest-use fixture 

(in.) 2.2 2.2 2.2 2.2

Flow speed highest use fixture (ft/s) 

(TLV, Inc. 2015) 0.75 0.75 0.75 0.75

Fixtures in zone 1.32 1.32 1.32 1.32
DOE/GO-102016-4735 ▪ February 2016

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