Measure Guideline: Heat 

Pump Water Heaters in 

New and Existing Homes

C. Shapiro, S. Puttagunta, and D. Owens

Consortium for Advanced Residential Buildings 

(CARB)

February 2012
NOTICE

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

any agency thereof. The views and opinions of authors expressed herein do not 

necessarily state or reflect those of the United States government or any agency 

thereof.

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Measure Guideline: Heat Pump Water Heaters in New

and Existing Homes

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by:

Carl Shapiro, Srikanth Puttagunta, and Douglas Owens

Steven Winter Associates, Inc.

of the

Consortium for Advanced Residential Buildings (CARB)

50 Washington Street

Norwalk, CT 06854

NREL Technical Monitor: Cheryn Engebrecht

Prepared under Subcontract No. KNDJ-0-40342-02

February 2012
[This page left blank]
iii

Contents

List of Figures ............................................................................................................................................ iv

List of Tables ............................................................................................................................................... v

Definitions................................................................................................................................................... vi

Foreword.................................................................................................................................................... vii

Acknowledgements .................................................................................................................................. vii

Progression Summary............................................................................................................................. viii

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

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

1.2 What Are Heat Pump Water Heaters? .................................................................................2

2 Cost and Performance ......................................................................................................................... 3

2.1 Performance Metrics...........................................................................................................3

2.2 Energy and Cost Savings.....................................................................................................3

2.3 What Affects Performance?.................................................................................................5

2.3.1 Hot Water Usage......................................................................................................5

2.3.2 Ambient Temperature ..............................................................................................8

2.3.3 Interaction with Space Conditioning Systems.........................................................9

2.3.4 Inadequate Space .....................................................................................................9

2.4 Dehumidification Potential ................................................................................................10

2.5 Reliability and Safety.........................................................................................................10

3 HPWH Implementation Details .......................................................................................................... 11

3.1 Selecting the Best Location for a HPWH ..........................................................................11

3.1.1 Space Requirements...............................................................................................11

3.1.2 Conditioned or Unconditioned Space? ..................................................................12

3.2 Proper Installation and Maintenance .................................................................................14

3.2.1 Managing Condensate............................................................................................14

3.2.2 Heat traps...............................................................................................................15

3.2.3 Mixing Valves and Setpoint Temperature .............................................................16

3.2.4 Filter Maintenance .................................................................................................16

3.2.5 Typical Maintenance (for HPWH or ERWH) .......................................................17

References................................................................................................................................................. 19

Appendix A: Measure Implementation Checklist................................................................................... 21

Appendix B: HPWH Installation Checklist (leave behind with unit)..................................................... 23
iv

List of Figures

Figure 1. HPWH operation.......................................................................................................................... 2

Figure 2. Efficiency and electricity usage as a function of hot water demand..................................... 6

Figure 3. Majority heat pump usage to meet demand............................................................................. 7

Figure 4. Majority electric resistance usage to meet demand................................................................ 7

Figure 5. Efficiency of a 50-gal HPWH operating in heat pump mode .................................................. 8

Figure 6. Electricity usage for heat pump and lower element vs. inlet air temperature...................... 9

Figure 7. HPWH installed with adequate clearances............................................................................. 12

Figure 8. Improper HPWH with air discharge facing wall ..................................................................... 12

Figure 9. HPWH installed in boiler room ................................................................................................ 14

Figure 10. Condensate problems from improper installation .............................................................. 15

Figure 11. Proper HPWH installation ...................................................................................................... 15

Figure 12. HPWH without heat traps ....................................................................................................... 15

Figure 13. HPWH with heat traps............................................................................................................. 15

Figure 14. Heat pump water heater with mixing valve .......................................................................... 16

Figure 15. Dirty filter: Finger rubbed against filter to show accumulation of dirt.............................. 17

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

List of Tables

Table 1. 2005 RECS Data Sample of Households with ERWHs (Franco et al. 2010)............................ 1

Table 2. Key Specifications of Some HPWHs Currently Available in the U.S. Market......................... 1

Table 3. Comparison of Water Heaters by Fuel Type.............................................................................. 4

Table 4. HPWH vs. ERWH (U.S. Government EnergyGuide Labels)...................................................... 4

Table 5. Expected Annual Energy Savings by House Size..................................................................... 5

Table 6. Weight, Volume, Clearances, and Operating Temperatures for Various HPWH models .... 11

Table 7. Impact of Placing HPWH in Conditioned Space on Space Conditioning Usage ................. 13

Table 8. Time/Temperature Relationships in Scalds (Shriners Burn Institute) .................................. 16

Table 9. Water Heater Maintenance Schedule ....................................................................................... 17

Unless otherwise noted, all tables were created by the CARB team.
vi

Definitions

CARB Consortium for Advanced Residential Buildings

COP Coefficient of Performance

DHW Domestic Hot Water

EF Energy Factor

ERWH Electric Resistance Water Heater

GE General Electric

IECC International Energy Conservation Code

NREL National Renewable Energy Laboratory

ROI Return On Investment

SPB Simple Payback Period
vii

Foreword 

Heat pump water heaters (HPWHs) promise to significantly reduce energy consumption for domestic hot 

water (DHW) over standard electric resistance water heaters (ERWHs). While ERWHs perform with 

energy factors (EFs) around 0.9, new HPWHs boast EFs upwards of 2.0. High energy factors in HPWHs

are achieved by combining a vapor compression system, which extracts heat from the surrounding air at 

high efficiencies, with electric resistance element(s), which are better suited to meet large hot water 

demands. Swapping ERWHs with HPWHs could result in roughly 50% reduction in water heating energy 

consumption for 35.6% of all U.S. households.

This Building America Measure Guideline is intended for builders, contractors, homeowners, and policymakers. While HPWHs promise to significantly reduce energy use for DHW, proper installation, 

selection, and maintenance of HPWHs is required to ensure high operating efficiency and reliability. This 

document is intended to explore the issues surrounding HPWHs to ensure that homeowners and 

contractors have the tools needed to appropriately and efficiently install HPWHs.

Section 1 of this guideline provides a brief description of HPWHs and their operation. Section 2

highlights the cost and energy savings of HPWHs as well as the variables that affect HPWH performance, 

reliability, and efficiency. Section 3 gives guidelines for proper installation and maintenance of HPWHs, 

selection criteria for locating HPWHs, and highlights of important differences between ERWH and 

HPWH installations.

Throughout this document, CARB has included results from the evaluation of 14 heat pump water heaters 

(including three recently released HPWH products) installed in existing homes in the northeast region of 

the United States.

Acknowledgements 

This guideline is the product of a collaborative effort. The authors acknowledge the funding and support 

of the US Department of Energy’s Building America Program and our utility sponsors: National Grid, 

NSTAR, and Cape Light Compact. Special thanks to Keith Miller and Andrew Wood of National Grid, 

Richard Moran of NSTAR, and Margaret Song of Cape Light Compact. 
viii

Progression Summary

Determine the interaction with 

cooling and heating equipment: 

Hot climates will have a net cooling 

benefit, while cold climates will 

have a net heating penalty (see 

Sections 2.3.3 and 3.1.2). 

Generally, homes in climate zones 

1 and 2 have a net cooling benefit.

If Installing in Conditioned 

Space

Assess Available Location:

• Sufficient room volume

• Adequate ambient 

temperature

• Noise will not interfere 

with living spaces

• Drain is available for 

condensate collection

If Installing in Semi-/UnConditioned Space

Select Available Location:

• Sufficient room volume

• Noise will not interfere with 

living spaces

• Drain is available for 

condensate collection

Fails

Passes Install as directed

Consider alternative high 

efficiency water heater options, 

or evaluate the efficiency 

impact of minimized heat pump 

operation. Fails

If Installing in an Attached 

Garage

Select Available Location:

• Drain is available for 

condensate collection

Hot Climate Cold/Mixed 

Climate

Passes

Fails

Fails
1

1 Introduction

1.1 Background

Heat pump water heaters (HPWHs) promise to significantly reduce energy consumption for domestic hot 

water (DHW) over standard electric resistance water heaters (ERWHs). While ERWHs perform with 

energy factors (EFs) around 0.9, new HPWHs boast EFs upwards of 2.0. High energy factors in HPWHs

are achieved by combining a vapor compression system, which extracts heat from the surrounding air at 

high efficiencies, with electric resistance element(s), which are able to help meet large hot water 

demands. Water heating is the third largest contributor to residential energy consumption, after space 

heating and space cooling (EERE 2011). Swapping ERWHs with HPWHs could result in roughly 50% 

reduction in water heating energy consumption for 35.6% of all households nationally, as shown in Table 

1.

Table 1. 2005 RECS Data Sample of Households with ERWHs (Franco et al. 2010)

Census Region

Fraction of Households 

with ERWH by Region

Northeast 17.1%

Midwest 26.7%

South 58.8%

West 21.5%

National 35.6%

While HPWHs are not new, products designed for the residential market have achieved minimal market 

penetration in the past, primarily because past products were produced by smaller, niche-market 

manufacturers, encountered reliability issues, and operated with limited market infrastructure. Although 

HPWHs were first commercialized in the 1980s, they were typically add-ons to existing ERWHs, which 

required specialized knowledge for installation and often required both an HVAC contractor and a 

plumber to install the system. The development of drop-in HPWHs allowed for easy installation by a 

single trade (Tomlinson 2002).

Recently, major manufacturers, such as General Electric (GE), Rheem, AO Smith, and Stiebel-Eltron, 

have introduced “drop-in” HPWHs (Table 2). The development of these models has been fueled by the 

large electric water heater replacement market and ENERGY STAR® certification of many HPWHs, 

which often allows for state, federal, local, and utility rebates, tax credits, and other incentives. 

Furthermore, the new federal water heater standard, which takes effect in 2015, mandates EFs around 2.0 

for all new electric storage water heaters with capacities greater than 55 gallons (Federal Register 2010). 

This regulation effectively mandates that water heaters be HPWHs in applications with large hot water 

demands and the need for electric storage water heaters. 

Table 2. Key Specifications of Some HPWHs Currently Available in the U.S. Market

Model

Capacity 

(gal)

Energy 

Factor

First Hour 

Rating 

(GPH)

GE GeoSpring 50 2.35 63.0

AO Smith Voltex 60 / 80 2.33 68.0 / 84.0

Stiebel Eltron Accelera300 80 2.51 78.6

Rheem EcoSense 40 / 50 2.00 56.0 / 67.0

AirGenerate ATI 50 / 66 2.39 / 2.40 60.0 / 75.0
2

1.2 What Are Heat Pump Water Heaters?

In residential applications, the most common water heater appliances are electric resistance with storage 

tank (ERWH), natural gas with storage tank, and tankless natural gas. HPWHs are designed as 

replacements for standard ERWHs and are able to achieve higher energy factors by adding an additional 

heating mechanism to existing ERWH designs. The primary heating mechanism is a heat pump 

refrigeration cycle (like those in a refrigerator or air conditioner, but operating in reverse) that transfers 

heat from the surrounding air to the water stored in the tank (Figure 1). Auxiliary electric resistance 

elements are also included for reliability and quicker recovery. Unlike most previous models, most

current HPWHs are truly hybrids: They integrate a heat pump and electric resistance element(s) into a 

single storage tank.

Figure 1. HPWH operation

The heat pumps can heat water in the storage tanks at high efficiencies, but the heat pumps have heating 

capacities lower than those of traditional electric resistance elements. Typical 4.5-kW electric resistance 

elements can reliably heat over 20 gallons of water per hour (GE 2011), whereas the heat pump has a 

longer heating rate (GE claims 8 gallons per hour at 68°F air temperature). The efficiency of a HPWH 

will vary considerably based on several operating parameters, such as inlet water temperature, tank 

temperature, inlet air temperature, and temperature set point. 

These units often have several modes of operation, such as hybrid mode, heat pump mode, and electric 

resistance mode. The names of these modes differ by manufacturer, but most models include some 

combination of the above. The hybrid mode uses both the electric resistance element(s) and the heat pump 

to meet demand, but uses the heat pump whenever possible to maximize the efficiency of the unit. Heat 
3

pump mode includes only heat pump operation, which improves the efficiency of the unit, but reduces the 

recovery capacity of the water heater. Electric resistance mode works like a traditional ERWH and can be 

used when the ambient temperature of the space is inadequate or there is a problem with the heat pump.

2 Cost and Performance

Using HPWHs is a potentially cost-effective method of substantially reducing energy use for DHW when 

compared to use of electric resistance water heaters. Section 2.2 explores the energy and cost savings of 

HPWHs, while Section 2.3 explores the variables that affect the overall performance of HPWHs. Sections 

2.4 and 2.5 discuss the dehumidification potential, reliability, and safety of HPWHs.

2.1 Performance Metrics

The efficiency of residential electric water heaters in the United States is measured and reported using the

energy factor (EF) value. The energy factor represents the efficiency of the electric element and tank 

losses under a consistent, 24-hour test procedure. In this procedure, 64.3 gallons of water are drawn from 

the tank in six equal draws spaced one hour apart. The temperature of the drawn water must be 135±5 ̊F 

and the ambient temperature is 67.5 ̊F. The energy factor is simply the ratio of energy output to energy 

input during the test procedure (Burch and Erickson 2004; Federal Register 1998).

Since the energy factor is defined under the specific test conditions outlined above, for a unit that operates 

under real-world conditions or conditions different than the standard test, the coefficient of performance 

(COP) is the term used here to describe the efficiency of the unit under the measured conditions. Like EF, 

COP is the unit-less ratio of energy output to energy input during its operation.

When comparing energy use of water heaters using different fuels, EF or COP can be misleading because 

energy use is only measured at the home and does not include energy lost to extraction, conversion, or 

transmission of the energy. Therefore, water heaters using different fuels should be compared using a 

different metric. While energy usage is usually measured in site energy, which is the energy used at the 

home and is typically measured at a utility meter in units of kWh (electricity), therms (natural gas), or 

gallons (fuel oil or propane), a better metric for measured energy usage is source energy, which is the sum 

of energy used at the home and the energy lost to extraction, conversion, or transmission. Site energy 

easily can be converted to source energy using a site-to-source ratio (Deru and Torcellini 2007) for the 

given fuel. 

When comparing water heaters that use different fuels, this guideline will use two metrics: cost to deliver 

each unit of water heating energy ($/delivered mmBTU) and “source COP,” which is the efficiency of 

converting source energy into water heating energy. These metrics include the efficiency of extraction, 

conversion, and transmission.

2.2 Energy and Cost Savings

Traditional ERWHs are an inefficient and expensive form of water heating. As shown in Table 3 , electric 

resistance water heating has the lowest source COP and the highest cost per mmBTU of delivered water 

thermal energy. On the other hand, HPWHs have efficiencies and operating costs similar to natural gas 

storage water heaters, making HPWHs an excellent choice for homeowners who currently use an electric 

resistance, fuel oil, or propane water heater and do not have access to natural gas. Replacement of natural 

gas water heaters with HPWHs is not recommended in heating dominated climates because HPWHs will 

increase the load on the space heating system without a similar benefit to the space cooling system.
4

Table 3. Comparison of Water Heaters by Fuel Type

Water Heater 

Type

Storage 

Tank

Site-to-Source 

Ratio Fuel Cost EF Source COP

$/Delivered 

mmBTU

Electric 

Resistance Tank 3.365 $0.1126/kWh 0.90 0.27 $36.67 

Heat Pump Tank 3.365 $0.1126/kWh 2.00 0.59 $16.50 

Fuel Oil Tank 1.158 $2.8/gal 0.59 0.51 $34.22 

Natural Gas Tank 1.092 $1.1633/therm 0.59 0.54 $19.72 

Natural Gas Tankless 1.092 $1.1633/therm 0.82 0.75 $14.19 

Condensing 

Natural Gas Tankless 1.092 $2.03/gal 0.94 0.86 $12.38 

Propane Tank 1.151 $2.03/gal 0.59 0.51 $37.40 

Marketed as replacements for electric resistance units, HPWHs promise to save considerable electric 

energy and money over traditional ERWHs. According to the U.S. government EnergyGuides for a 50 

gallon ERWH with an EF of 0.90 and a HPWH with an EF of 2.35, a HPWH could save 2,684 kWh per 

year for an average family (Table 4). These water heaters are considerably more expensive to install than 

traditional ERWHs, but electric savings will likely save more money over the course of the water heater’s 

life. Table 4 shows the installation and annual operating costs, according to the National Renewable 

Energy Laboratory’s (NREL) National Residential Efficiency Measures Database and the U.S.

government Energy Guide labels. 

Table 4. HPWH vs. ERWH (U.S. Government EnergyGuide Labels)

Water Heater

Annual Electric 

Usage

(kWh)†

Installation 

Cost*

Annual 

Operating 

Costs†

HPWH (50 gal, EF = 2.35) 1,856 $2,100 $198

ERWH (50 gal, EF = 0.90) 4,879 $590 $520

* NREL National Residential Efficiency Measures Database

† US Government Energy Guide Labels

Two methods of evaluating the cost effectiveness of energy efficiency measures are simple payback 

(SPB) and return on investment (ROI). The SPB period is the ratio of incremental initial cost (dollars) to 

annual energy savings (dollars/year).

The ROI is the ratio of net proceeds to the investment costs.
5

Using the costs and savings in Table 4, the SPB period for HPWHs is 4.7, and the ROI is 113%.

2.3 What Affects Performance?

Although the cost and energy savings discussed in the sections above are quite compelling, real world 

savings of each individual HPWH may be vastly different than those described above. Unlike 

conventional ERWHs, the efficiency of HPWHs is hard to predict and strongly dependent on hot water 

usage patterns (see Section 2.3.1) and ambient temperature (see Section 2.3.2). Furthermore, HPWH 

operation may impact the space conditioning equipment, increasing heating loads and decreasing cooling 

loads (see Section 2.3.3). Inadequate space and ambient temperature will also markedly reduce HPWH 

efficiency (see Sections 2.3.4 and 2.3.4).

2.3.1 Hot Water Usage

The primary driver of the efficiency and energy usage of a HPWH is hot water demand (e.g. gallons used 

per day). As with traditional ERWHs, standby losses reduce overall efficiency, particularly at lower hot 

water demands. Unlike ERWHs, however, HPWHs experience a reduction in efficiency as electric 

resistance heating is required to meet larger hot water demands. 

There are two ways in which hot water consumption affects efficiency. Electricity consumption certainly 

increases with overall water consumption (i.e. average gallons used per day). However, electric 

consumption is even more dependent upon the intensity of hot water use. As the data below show, during 

intense, high-volume hot water draws, a hybrid HPWH will often operate in electric resistance mode. 

Electric resistance can provide more hot water faster, but it also consumes at least twice the electricity 

when compared to heat pump mode.

Figure 3 shows one day’s worth of data where a HPWH uses the heat pump to satisfy all hot water needs. 

Figure 4 shows the same HPWH relying exclusively on the electric resistance elements to meet demand 

Supporting Research

Field evaluations suggest that a 50-gallon HPWH has the potential to save a typical home 1,500 to 2,200 

kWh per year, which represents a 45%-65% reduction in electricity usage for domestic hot water. These 

results are not comparable to U.S. government estimates because they reflect varying household usage 

patterns and, in some cases, the operation of the electric resistance element that reduces overall efficiency. 

Utilizing a TRNSYS model, actual household usage data for a new 50-gallon HPWH were compared to a 

typical 50-gallon ERWH with an EF of 0.92. The expected lifetimes of these units are 10 years, and 13 

years, respectively. Using the Building America Standard Benchmark DHW Schedules for 1, 2, 3, 4 and 5 

bedrooms (Hendron et al. 2010), expected annual energy savings for 1, 2, and 3+ bedroom houses are 

between 1,750 and 2,200 kWh per year (Table 5). 

Table 5. Expected Annual Energy Savings by House Size

Number 

of 

Bedrooms

Average 

Daily Hot 

Water 

Usage 

(Gallons)

Expected 

Annual 

Energy 

Savings 

(kWh)

Annual 

Utility 

Bill 

Savings

Return on 

Investment

Payback 

Period 

(years)

1 35 1,750 $221 46% 6.6

2 45 2,000 $260 72% 5.8

 3+ 55 2,200 $286 89% 5.3
6

for a day with the same total hot water demand (70 gallons). Each data point in these charts is the 

totalized consumption over a 15 minute period. The first figure has a distribution of demand across the 

day, while the second day has large, concentrated draws during the afternoon and evening.

Supporting Research

Overall efficiency peaks around 20-30 gallons per day and decreases with increased demand due to an 

increase in hot water electric resistance element use. Overall electric usage strictly increases with 

domestic hot water demand. Figure 2 shows the average COP and electricity used for one HPWH model 

monitored during CARB’s HPWH evaluation. These curves are smoothed fits to daily data and are meant 

to show the effect of hot water usage on efficiency and electricity usage.

Figure 2. Efficiency and electricity usage as a function of hot water demand

0 10 20 30 40 50 60 70 80 90 100

0

0.5

1

1.5

2

2.5

Average COP

Daily Hot Water Usage (gallons/day)

0 10 20 30 40 50 60 70 80 90 100

0

4

8

12

16

20

Average Electricity Used (kWh/day)

Average COP

Average Electricity Used
7

Figure 3. Majority heat pump usage to meet demand

Figure 4. Majority electric resistance usage to meet demand

0

200

400

600

800

1000

1200

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

HW Used (Gallons)

Energy Used (Wh)

HW Use Upper Elelment Lower Element Heat Pump

0

200

400

600

800

1000

1200

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0:00 2:00 4:00 6:00 8:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 0:00

HW Used (Gallons)

Energy Used (Wh)

HW Use Upper Elelment Lower Element Heat Pump
8

2.3.2 Ambient Temperature

The efficiency of a HPWH increases substantially with increased ambient temperature (i.e. the air 

temperature of the space where the HPWH is located). Heat pumps become much more efficient 

when the heat source (in this case the ambient air) becomes warmer. Warmer air also reduces standby 

losses.

The HPWHs will only operate in heat pump or hybrid mode if the ambient temperature of the air 

entering the water heater is between ~45°F and ~110°F. When the temperature of the incoming air 

drops below the minimum temperature, the HPWH will switch into electric resistance mode, 

reducing the efficiency of the unit. In practice, the temperature of the space must be several degrees 

above the minimum temperature due to the cooling effect of the heat pump operation, which drops 

the temperature of the space. On the lower end of this temperature range, system efficiency can be 

compromised due to: 

• Increased electric resistance back-up heating

• Decreased hot water output

• Decreased hot water temperature rise.

Supporting Research

Figure 5 shows the effect of ambient temperature on the expected performance of a HPWH operating in 

heat pump mode. Higher ambient temperatures result in considerably higher COPs. At increased water 

use levels, an increase in ambient temperature from 50°F to 80°F results in an increase in COP of 

approximately 0.5.

Figure 5. Efficiency of a 50-gal HPWH operating in heat pump mode 

0 10 20 30 40 50 60 70 80 90 100

0

0.5

1

1.5

2

2.5

3

3.5

4

DHW Demand (Gallons/Day)

Coefficient of Performance

Daily Values

50°F

60°F

70°F

80°F

Ambient Temperature (°F)

45

50

55

60

65

70

75

80

85
9

2.3.3 Interaction with Space Conditioning Systems

As mentioned above, HPWHs transfer heat from the ambient air to water; this means HPWHs can have a 

significant impact on the heating and cooling load of a building if the HPWH is installed in conditioned 

space. HPWHs may reduce the ambient temperature 2F°-6°F when in operation (Stiebel- Eltron 2010), 

though this is heavily dependent on HPWH run time and the space in which the HPWH is located. Often,

HPWHs are touted as providing free energy due to COPs greater than 1.0, but when located within the 

building envelope, heat moved into the storage tank by a heat pump typically needs to be replaced by the 

home’s heating system. HPWHs can extract between 4 and 11 MMBTU/year of energy from the 

surrounding space. In hot climates, locating the HPWH in attached garages is an excellent way to 

optimize water heating performance without concern for the cooling effect of the unit.

2.3.4 Inadequate Space

The HPWH must be able to extract sufficient energy from the surrounding air, and the energy available in 

the air is primarily a function of the size of the space. Therefore, HPWHs must be installed in rooms with 

adequate volume to ensure efficient operation (see manufacturer literature for space requirements). 

Adequate clearances must be provided to allow for proper airflow and maintenance (see Section 3.1.1). If 

a unit is installed in an area with insufficient space, the space can experience a dramatic reduction in 

temperature during HPWH operation.

Supporting Research

As shown in Figure 6, heat pump operation dropped the ambient temperature by over 4°F, from 49°F to 

near 45°F, which is the minimum allowable ambient temperature for this unit. Colder air temperatures 

forced the electric resistance elements to turn on to meet hot water demand.

Figure 6. Electricity usage for heat pump and lower element vs. inlet air temperature

0

200

400

600

800

1000

1200

1400

43.0

44.0

45.0

46.0

47.0

48.0

49.0

50.0

Electricity Usage (Wh)

Inlet Air Temperature (F)

Inlet Temperature Heat Pump Energy Lower Element
10

2.4 Dehumidification Potential

Because HPWHs remove heat from the ambient air using a heat pump refrigeration cycle, they also

remove moisture from the air. The water vapor in the air will condense as it passes across the HPWH’s 

evaporator coils and, as a result, will provide dehumidification. This has the potential to reduce the need 

for dehumidifiers in damp spaces, such as unconditioned basements. Although the dehumidification is not

predictable, because it relies on operation of the HPWH, the HPWH can reduce the energy consumed by 

dehumidifiers in these spaces.

2.5 Reliability and Safety

Integrated (or “drop-in”) HPWHs are a relatively new technology that was first commercialized in the 

early 2000s. Earlier models were “add-on” configurations that heated the water outside of the storage 

tank. Unfortunately, the first commercialized, integrated HPWHs experienced problems with reliability 

and safety. 

Although the higher complexity of HPWHs over standard ERWHs may lead to greater reliability issues, 

so far modern HPWHs do not seem to be experiencing the same reliability issues that plagued earlier 

models. An accelerated durability test of older HPWH models performed at Oak Ridge National 

Laboratory found no long term reliability issues with these models (Baxter and Linkous 2004). These 

early results suggest that modern HPWHs may last as long as traditional ERWHs under extended 

operation.

Supporting Research

At one test site, the HPWH was installed in a location with inadequate space and showed a significant 

reduction in efficiency. The HPWH was installed in a small, unconditioned basement mechanical 

room with a door that was kept closed. The mechanical room’s area was approximately 440 ft3

, 

significantly less than the required 750 ft3 for the unit, contained a washer and dryer, and was used 

for storage. The overall COP of the unit was 30% lower than the expected COP of a HPWH installed 

with adequate space.

Supporting Research

In 2004, evaluation of an early integrated HPWH, the WatterSaver HPWH, demonstrated effective COPs, 

but some consistent drawbacks with the systems and their daily operation were identified, such as 

excessively hot water temperature. Monitoring showed that water temperature near the top of the tank 

often reached more than 150°F, partly because of excessive tank stratification – water temperatures near 

the top could be 50°F higher than temperatures near the bottom. In fact, high-temperature switches in 

many of the systems shut down the water heaters completely (high-temp safety switches are designed to 

turn off water heaters when temperatures reach 170°F). Control boards were also replaced because of 

problems with exposure to hot and humid conditions. Ultimately, because of the problems with installed 

performance and a nonexistent service infrastructure, this product is no longer on the market.

Monitoring of the current 14 HPWHs, however, has shown no issues with safety to date. Only one 

unit experienced a heat pump failure shortly after installation, but was quickly repaired by an 

authorized service provider. Upon failing, the unit switched from hybrid mode to electric mode and, 

as a result, the home did not experience a loss of hot water. Furthermore, all of the HPWHs under 

evaluation have yet to display problems with excessive or inadequate hot water temperatures.
11

3 HPWH Implementation Details

As noted in the introduction, hybrid heat pump water heaters are new to the mainstream market. Installing 

contractors should be aware that installation of these units is not as straightforward as a standard electric 

resistance water heater. Heat pumps require special attention to the air space (to ensure adequate air flow) 

around the unit and require condensate collection and removal. Installers may not be familiar with these 

units or heat pump models in general, and it can be difficult to install these units in existing homes. 

3.1 Selecting the Best Location for a HPWH

Selecting an appropriate location for a standard ERWH is relatively straightforward. Any space large 

enough for the water heater, piping, and servicing can be appropriate for an ERWH. However, HPWHs 

require special consideration as they require more space (see Section 2.3.4) and weigh more than 

traditional ERWHs. The added weight of these units, due to the heat pump components, may mean that

two or more people are required to move and install the unit. Furthermore, the best location must be 

chosen with respect to the interaction with the space conditioning equipment, the ambient temperature of 

the space, and noise (see Section 3.1.2). For reference, Table 6 lists the weight, volume, clearance, and 

operating temperature requirements for several current HPWH models (this is presented as an example; 

for accurate information, refer to up-to-date literature for specific HPWHs).

Table 6. Weight, Volume, Clearances, and Operating Temperatures for Various HPWH models

Model

Dry 

Weight 

(lbs)

Wet 

Weight 

(lbs)

Minimum 

Room 

Volume 

(ft3)

Minimum Clearances HP Inlet Air

Operating 

Temperature

(°F)

Air 

Inlet

Air 

Outlet Front Rear Top

GE 190 602 700 7" 7" 5.5" 5.5" 14" 45-120

Rheem 197 576/680 1,000 N/A N/A N/A 2" 8" 40-120

AO 

Smith

332*/

410*

827/

1,069 750 3' 5' 2' 6" None 45-109

StiebelEltron 287 952 500 16" 15.75" 8" 8" 16" 42-108

* shipping weight

3.1.1 Space Requirements

The HPWHs require more space than traditional 

ERWHs because of their additional height, 

weight, required air volume, and clearance 

requirements; HPWHs are generally taller and 

heavier than traditional ERWHs. Measures to 

manage condensate, such as placing the unit on 

blocks (see Section 3.2.1), may further increase 

the height requirements of HPWHs. The 

additional weight of the unit, particularly larger 

capacity models, may require reinforcement of 

the floor to ensure structural soundness.

Because HPWHs extract energy from their 

surrounding environment (see Section 1.2), 

enough air volume and adequate clearances must 

be provided to allow for proper operation of the 

unit. Improperly placed HPWHs are significantly 

HPWH Space Requirements Checklist

 Does the room meet the volume requirements of the 

unit (> 750 ft3

)?

 Are the ceilings high enough to accommodate the 

extra height of the HPWH?

 Is there adequate space to allow maintenance of the 

heat pump components?

 Can the HPWH be placed in the room such that 

there is sufficient clearance for airflow around the 

unit?

 Is there enough clearance for removal and cleaning 

of the air filter?

 Is the floor able to support the additional weight of 

the HPWH?
12

less efficient than properly installed units (see Section 2.3.4). Generally, HPWHs must be installed in a 

room with a volume of at least 750 ft3

, which corresponds to a 10 ft by 10 ft room with 7’6” ceilings. 

Furthermore, HPWHs require larger clearances for proper operation. Air entry and discharge must be free 

of obstructions to provide proper air circulation and ensure a continuous supply of fresh air. Figure 7

shows a properly installed HPWH with adequate clearances at the air entry and discharge, while Figure 8

shows a poorly installed unit with the air discharge directed towards a wall. Added clearances are also 

required for removal and cleaning of the air filter and for servicing of the unit. Piping installation must be 

carefully considered to prevent the pipes from blocking the air filter or maintenance panels. 

Figure 7. HPWH installed with adequate 

clearances

Figure 8. Improper HPWH with air discharge 

facing wall

3.1.2 Conditioned or Unconditioned Space?

When selecting an appropriate location for a HPWH, the interaction with the heating and cooling system 

must be closely considered. As mentioned in Section 2.3.3, HPWHs extract heat from the surrounding air 

and therefore increase heating loads and decrease cooling loads when installed in conditioned spaces. An 

analysis of the total impact on heating and cooling source energy usage (Table 7) reveals that for the vast 

majority of the United States, there is a net potential heating penalty on source energy usage for space 

conditioning. Cities in climate zone 2 may have a net potential cooling benefit. If the decision is made to 

relocate an interior water heater to a semi-conditioned space (i.e. garage or basement), consideration 

needs to be given regarding the impact on distribution system performance and hot water waiting times.
13

Table 7. Impact of Placing HPWH in Conditioned Space on Space Conditioning Usage

City

Climate 

Zone HDD65 CDD65 Potential Impact

Atlanta, GA 3A 2,694 1,841 Heating Penalty

Baltimore, MD 4A 4,567 1,228 Heating Penalty

Boston, MA 5A 5,621 750 Heating Penalty

Chicago, IL 5A 6,311 842 Heating Penalty

Denver, CO 5B 5,942 777 Heating Penalty

Houston, TX 2A 1,414 3,001 Cooling Benefit

Orlando, FL 2A 544 3,379 Cooling Benefit

Phoenix, AZ 2B 941 4,557 Cooling Benefit

San Francisco, CA 3C 2,708 142 Heating Penalty

Seattle, WA 4C 4,729 177 Heating Penalty

Conditioned Space

In climates with a net heating penalty, it is not advisable to place HPWHs in conditioned space without 

further exploring the potential impact. In locations with potential cooling benefit, HPWHs may be placed 

in conditioned space, although special consideration must be used when deciding the best location for the 

HPWH. Although these units have a potential to reduce overall space conditioning loads, the cooling 

from these units may lead to over-cooling of the space because the operation of the unit is not controlled 

by a thermostat. Follow these guidelines when choosing a proper location for the HPWH:

• Never place the unit close to a thermostat, as this may result in improper heating or cooling 

of the home. 

• Never place the unit near the kitchen. Oils from cooking can ruin the unit.

• Place the unit in a location that is not sensitive to 

colder temperatures.

• Make sure to meet the manufacturer’s space 

requirements (e.g. Section 3.1.1). Do not place the 

unit in a closet unless the closet door has a 

louvered door. Even with a louvered door, locating 

the HPWH in a closet will likely reduce overall 

performance of the unit.

• Noise may be an issue because the HPWH uses a 

compressor and fan to move air through the unit. 

Do not place the unit near bedrooms or other 

noise-sensitive locations. 

Unconditioned Space

In most U.S. climates, HPWHs can be placed in unconditioned or semi-conditioned spaces. Semiconditioned spaces are spaces that are inside the thermal boundary, but not directly heated or cooled. The 

most common semi-/unconditioned locations are garages and basements. Crawlspaces are generally too 

short for HPWHs, and HPWHs are typically not recommended to be placed in attics (because of potential 

for water leaks, weight of unit, ambient temperature that fluctuates outside the heat pump’s operating 

range, etc.).

When installing a HPWH in a room 

with a furnace, ensure that the unit 

does not interfere with operation of 

the furnace. Air flows inside the room 

will change as a result of HPWH 

installation.
14

Interesting Fact

At one site in CARB’s evaluation of 14 HPWHs, the unit was 

placed in an unfinished basement in the mechanical room next to 

the boiler. The waste heat from the boiler increased the ambient 

temperature of the room in the winter, meaning that the room 

was 70°F or warmer throughout winter. The waste heat improves 

the efficiency of the HPWH and minimizes the impact of the 

HPWH on the space heating loads of the house.

The primary consideration for unconditioned spaces is the size of the room (see Section 3.1.1) and the 

ambient temperature of the space. The minimum temperature of the space should not be below 50°F. 

Operation of the HPWH will result in a significant drop in ambient temperature, and such a drop may 

result in an air temperature below the minimum recommended operating temperature in heat pump mode

(see Section 2.3.2). HPWHs with electric resistance modes may be placed in colder basements, but the 

HPWH will not operate at its rated efficiency during colder months. In more temperate climates, the 

attached garage can be a suitable location, as long as plumbing lines are not too long and can be properly 

insulated. In colder climates, however, the basement will likely have the highest temperature of all 

unconditioned spaces.

 

Figure 9. HPWH installed in boiler room

3.2 Proper Installation and Maintenance

Good installers of HPWHs pay close attention to 

condensate management (Section 3.2.1), heat traps 

(Section 3.2.2), and mixing valves (if applicable, 

Section 1.1.1). Proper maintenance includes inspection 

of the condensate lines and regular cleaning of the air 

filter. Installations should always comply with local 

and state codes.

3.2.1 Managing Condensate

As warm, moist air travels over the evaporator coils of a HPWH, some moisture in the air will condense,

and the resulting condensate is removed from the unit through a condensate drain line. This condensate 

must be effectively removed to prevent damage to the unit. While manufacturer’s condensate 

requirements vary slightly, in the simplest configuration a hose is connected to the condensate line and 

properly pitched toward a drain in the floor. If a suitable drain is not available, a condensate pump must 

be installed to ensure that condensate is properly removed. Based on contractor feedback, a 240V 

condensate pump is recommended for this application to avoid potential call backs related to tripped 

ground-fault circuit interrupter (GFI) outlets used to power 120V condensate pumps. 

HPWH Installation Checklist

 Place the unit on blocks

 Install a drain pan

 Install a condensate pump, if applicable

 Install heat traps to prevent thermosiphoning

 Install a mixing valve, if applicable
15

To protect the unit from a condensate line failure or other condensate issue, HPWHs should be installed 

on blocks with a drain pan. These precautions prevent the unit from sitting in water and ensure that the 

condensing water is properly transferred to a drain.

Drain pans are used to capture overflow due to condensate pump failure, piping failure, and condensate 

line obstructions. Because HPWHs are relatively new to the mainstream market, the installers may not be 

aware of the need for drain pans. Given the low cost, all HPWHs should have a drain pan installed. 

Concrete blocks are often used to raise the bottom of the unit above the lip of the drain pan which 

prevents the bottom of the unit from resting in water (and possibly corroding should a leak occur). Figure 

10 shows a HPWH that does not properly remove condensate away from the unit into the drain. The unit 

ended up sitting in water due to a kinked condensate line. Figure 11 shows a proper HPWH installation, 

where the unit is set on blocks in a drain pan and a condensate pump is used. 

Figure 10. Condensate problems from 

improper installation

Figure 11. Proper HPWH installation

If the condensate line becomes clogged or kinked, the drain hose must be removed and cleared of any 

debris. The owner should periodically inspect and clear any debris from the condensate line to prevent 

condensate overflow.

3.2.2 Heat traps

Heat traps should be installed on all hot water systems to prevent thermosiphoning, which is the transfer 

of heat from the storage tank down the cold or hot water lines. Thermosiphoning reduces the efficiency of 

the unit by increasing the standby losses to the environment. Figure 12 shows a HPWH installed without 

heat traps, while Figure 13 shows a properly installed HPWH with heat traps.

Figure 12. HPWH without heat traps Figure 13. HPWH with heat traps
16

3.2.3 Mixing Valves and Setpoint Temperature

With any water heater that generates relatively high water temperatures a mixing valve should be installed 

to minimize the risk of burns or scalding (see Table 8). If a HPWH generates temperatures above 125F°-

130°F (or if the temperature is likely to be set above this), a mixing valve should be installed (Figure 14).

Table 8. Time/Temperature Relationships in Scalds (Shriners Burn Institute)

Temperature Time to Produce a Serious Burn

120 More than 5 minutes

125 1.5 – 2 minutes

130 About 30 seconds

135 About 10 seconds

140 Less than 5 seconds

145 Less than 3 seconds

150 About 1.5 seconds

155 About 1 second

 

Figure 14. Heat pump water heater with mixing valve

Just as a high water temperature could result in scalding, a low temperature could result in the growth of 

the bacterium Legionella, which causes lung infections. This bacterium thrives in warm water, but 

temperatures over 119°F will minimize Legionella growth. Temperatures above 122°F will kill 90% of 

the bacteria in 80-124 minutes, and temperatures above 140°F will kill 90% of the bacteria in 2 minutes 

(WHO 2007). Temperatures around 120°F (but not less than 119°F) are the recommended temperature set 

point to minimize scald potential and reduce standby losses while maintaining water quality. If the 

vacation mode of a water heater is used (or temperature setpoint lowered), ensure that the unit is given 

adequate time to recover to a temperature higher than 122°F for several hours upon return from vacation 

before using the hot water.

3.2.4 Filter Maintenance

If a HPWH has an air filter, the filter must be regularly cleaned to ensure that the unit runs at peak 

efficiency. In Figure 15, a HPWH with a dirty air filter is shown. On some units, the air filter is removed 

from the top of the unit, and therefore extra clearance must be provided to ensure that the unit’s filter can 

be properly cleaned.

Mixing Valves

The hot water outlet temperature may 

change over the course of the year, 

increasing during the summer as the mains 

temperature increases. 

HPWH Piping Issues

The inlet and outlet pipes of most ERWHs 

enter the top of the unit. Due to the inclusion 

of the heat pump at the top of the unit, some 

HPWHs have different locations and 

orientations of the water lines. In Figure 14, 

the water lines enter the unit at the side and 

are placed horizontally. This orientation will 

likely require additional plumbing.

Furthermore, the air filter in some units is 

placed near the water piping. As a result, the 

installer must pay close attention to the 

piping installation to avoid obstructing the 

air filter.
17

Figure 15. Dirty filter: finger rubbed against filter to show accumulation of dirt

3.2.5 Typical Maintenance (for HPWH or ERWH)

In addition to cleaning the air filter, both HPWHs and ERWHs require regular maintenance to ensure 

proper operation and extend the life of the unit. Table 9 lists the required maintenance items for water 

heaters and the recommended timing.

Table 9. Water Heater Maintenance Schedule

Maintenance Item When? Why?

Check temperature pressure relief 

valve Yearly Ensure proper operation

Discharge water from tank Monthly Prevent hard water deposits from 

accumulating

Inspection by qualified service 

provider Yearly Ensure proper operation
18

Check Temperature Pressure Relief Valve

Lift and release the lever handle on the temperature pressure relief valve (check manual for 

location).

Ensure lever moves freely.

Allow several gallons to flow through the discharge line to an open drain.

Discharge Water from Tank

Suspended solids in tap water may settle at the bottom of a water heater’s tank. To ensure that these solids 

do not collect at the bottom of the tank, a few quarts of water should be drained from the drain valve of 

the tank every month. See the section below for instructions for draining the tank. 

Draining the Tank

Note: Drainage hose should be rated for at least 180°F. Otherwise, turn off power to water heater and 

open hot water faucet until the water runs cold.

Shut off power to the water heater.

Turn off cold water supply.

Open a hot water faucet to allow air to enter the tank.

Attach a hose to the drain valve on the water heater and direct 

the stream of water to a drain.

Open the relief valve.

Drain water heater.

Close relief valve.

Disconnect hose from valve.

Turn on cold water supply.

Keep hot water faucet open until water runs through the faucet.

Close hot water faucet.

Turn on power to the water heater.

Inspection by Qualified Service Provider

Periodically contact a qualified electric appliance repair service provider to inspect the operating controls, 

heating elements, anode rod, and wiring.

Helpful Tip

Even new electrical 

appliances may make 

hissing or singing sounds 

during operation. 

However, if these noises 

increase excessively, the 

electric resistance elements 

may need cleaning. 

Contact a qualified 

installer or plumbing 

contractor to inspect the 

unit.
19

References

Amarnath, K. R.; Trueblood, C. (2010). “Heat Pump Water Heaters: Laboratory and Field 

Evaluation of New Residential Products.” Proc. Summer Study on Energy Efficiency in 

Buildings (1); American Council for an Energy-Efficient Economy; pp. 12-23.

AIL Research, Inc. (2001). “Northeast Utilities Heat Pump Water Heater Field Test: 30 Crispaire 

Installations.”

AIL Research, Inc. (2002). Nyle Heat Pump Water Heat Evaluation

A.O. Smith (2010). “VoltexTM Hybrid Electric Heat Pump Water Heater Installation Instructions 

and Use & Care Guide.”

Baxter, V.; Linkous, R. (2004). “Heat Pump Water Heater Durability Testing – Phase II.” Oak 

Ridge, TN: Oak Ridge National Laboratory; ORNL/TM-2004/111.

Burch, J.; Erickson, P. (2004). “Using Data to Derive Simulation-Model Inputs for Storage-Tank 

Water Heaters.” Portland, OR: Proceedings of the Solar 2004 Conference. pp. 393-398

[CARB 2010] Consortium for Residential Buildings (2010). “Retrofitting America: A 1970s 

Home Energy Efficiency Analysis.” 

http://carb-swa.com/articles/homepage/RetrofittingAmerica_1970sHomeAnalysis.pdf

Deru, M; Torcellini, P (2007). Source Energy and Emission Factors for Energy Use in Buildings. 

Golden, CO: National Renewable Energy Laboratory.

[EERE 2011] U.S. Department of Energy, Energy Efficiency and Renewable Energy; “Table 

2.1.5 2008 Residential Energy End-Use Splits, by Fuel Type (Quadrillian Btu).” Building Energy 

Data Book; http://buildingsdatabook.eren.doe.gov/TableView.aspx?table=2.1.5; Date Access: 

July 17, 2011.

Federal Register, (2010). Vol. 75, No. 73 p. 20114 10CFR 430. 

Federal Register, (1998). Vol. 63, No. 90 p. 25995 10CFR 430. 

Franco, V.; Lekov, A.; Meyers, S.; Letschert, V. (2010). “Heat Pump Water Heaters and 

America Homes: A Good Fit?” Proc. Summer Study on Energy Efficiency in Buildings (9); 

American Council for an Energy-Efficient Economy; pp. 68-79.

[GE 2010] General Electric (2010). “Owner’s Manual & Installation Instructions.” 49-50254 10-

09 JR

[GE 2011] General Electric (2011). “Water Heater FAQs: How long should my GeoSpring water 

heater run in order to reheat the water in the water heater?” http://www.geappliances.com/heatpump-hot-water-heater/water-heater-faq.htm#recoveryTime Accessed 25 April 2011

Glanville, P., and D. Kosar, 2011. Building America Industrialized Housing Partnership IISubtask 2.2.3: Efficient Hot Water and Distribution Systems Research. Gas Technology Institute 
20

project number 20970. and also, Pacific Gas & Electric Company, 2010. Laboratory Evaluation 

and Field Testing of Residential Heat Pump Water Heaters. PG&E Applied Technology Services 

Test Report #:491-10.04.

Hendron, B.; Burch, J.; Barker, G. (2010). “Tool for Generating Realistic Residential Hot Water 

Event Schedules.” New York, NY: SimBuild 2010. 

[IECC 2009] International Code Council, Inc. (2009). 2009 International Energy Conservation 

Code. Country Club Hills, IL.

[ORNL 2002] Oak Ridge National Laboratory (2002). “Field Tests of a ‘Drop-In’ Residential 

Heat Pump Water Heater.”

[PGEC 2009] Pacific Gas and Electric Company (2009). “Energy Performance Analysis for Heat 

Pump Water Heaters.” Application Assessment Report #0916.

Rheem (2009). “Use & Case Manual: Electric Residential Heat Pump Water Heaters.”

Stiebel-Eltron (2010). “Operating and Installation Manual: DHW Heat Pump Water Heater 

Accelera® 300.”

[SWS] National Renewable Energy Laboratory (2011). “Workforce Guidelines for Home Energy 

Upgrades.”

Tomlinson, J. J. (2002). “All Pumped Up: New heat pump water heaters consume half the energy 

of conventional electric-resistance ones.” Home Energy; November/December 2002; pp. 30-35.

Tomlinson, J. J.; Rice, C.K.; Baskin, E. (2005). “Integrated Heat Pumps for Combined Space 

Conditioning and Water Heating.” 8th IEA Heat Pump Conference Paper.

[WHO 2007] World Health Organization (2007). “Legionella and the Prevention of Legionellosis.” 

Yates, D. (2010). “Keep selling heat pump water heaters after tax credit expires.” Contractor 

Mag; http://contractormag.com/columns/yates/selling-pump-water-heateers-0610; June 9, 2010 

Accessed 25 April 2011.

Zogg, R. (2002). “Residential Heat Pump Water Heater Technology and Markets Seminar.” 

December 4-5, 2002; Portland, OR.
21

Appendix A: Measure Implementation Checklist

1. Select the best type of location for the HPWH. Determine the interaction with 

cooling and heating equipment. Should the unit be placed in conditioned space, semi-

/unconditioned space, or in an attached garage? Hot climates will have a net cooling 

benefit, while cold climates will have a net heating penalty (see Sections 2.3.3 and 3.1.2). 

Generally, homes in climate zones 1 and 2 have a net cooling benefit. For climate zones 1 

and 2, installation in an attached garage of unconditioned space may be appropriate.

2. Select available location. Can the HPWH be installed in the selected location? If the 

location does not meet the requirements then consider a new location or an alternative 

high efficiency water heater option, or evaluate the efficiency impact of minimized heat 

pump operation. 

Sufficient room volume ( 750 to 1,000ft3) YES NO

Adequate ambient temperature ( > 50°F) YES NO

There is sufficient space to meet clearance 

requirements YES NO

Noise will not interfere with living spaces YES NO

Drain is available for condensate removal YES NO

3. Can the floor support the unit? If not, reinforce as necessary.

4. Removal of older equipment (if applicable). In the case of existing home retrofits,

follow accepted industry procedures and practices as listed in the Standard Work 

Specification (SWS): 

a. Remove old water heater and associated components.

b. Seal any unused chimney openings.

c. Remove unused oil tank, lines, and associated equipment.

5. HPWH installation. Follow the guidelines for installation as listed in the Standard Work 

Specification (SWS). These requirements are as follows:

a. Repair any existing water leaks before installation.

b. Seal any penetrations to the exterior of the home created by the installation of the 

equipment.

c. Install an emergency drain pan a minimum of 4” above floor. Connect a 3⁄4” drain 

line or larger to tapping on pan and run to drain or pumped to daylight.

d. If needed, install a stainless steel bladder expansion tank will on the cold water 

side using a direct connection with no valves between the storage tank and 

expansion tank.
22

e. Correct temperature and pressure relief valve will be installed according to 

manufacturer specifications. Temperature and pressure relief valve discharge tube 

will terminate within 6” of the floor, or as prescribed by local code.

f. Install di-electric unions according to manufacturer specifications.

g. Discharge temperature will be set to not exceed 120° or as prescribed by local 

code.

h. Commissioning will be in compliance with manufacturer specifications and 

relevant industry standards. The following will be checked once the system has 

been filled and purged:

• Safety controls 

• Combustion safety and efficiency

• Operational controls

• Water leaks

• Local code requirements.

i. Occupants will be educated on the safe and efficient operation and maintenance of 

the system, including: 

• Adjustment of water temperature and target temperature per local code

• Periodic drain and flush 

• Expansion tank and backflow preventer ( no occupant maintenance 

required).

In addition to the requirements outlined by the SWS, remember to install the following items 

for HPWHs:

a. Place the unit on blocks.

b. Install a drain pan.

c. Install a condensate pump, if applicable.

d. Install heat traps to prevent thermosiphoning.

e. Install mixing valves, if needed.
23

Appendix B: HPWH Installation Checklist (leave behind with unit)

Home Address:____________________________________ City:______________ State:_____

Is the site suitable for a HPWH? Adequate Ambient Temperature ( > 50oF)

Condensate Drain Available

Noise will not Interfere with the Living Space

What HPWH is being installed? Manufacturer ____________________

Model # ____________________

Tank Size ______ Gallons

Are minimum requirements met? Sufficient Room Volume ( > ______ ft3)

Minimum Clearances:

Air Inlet ( > ______ in)

Air Outlet ( > ______ in)

Front ( > ______ in)

Rear ( > ______ in)

Top ( > ______ in)

Is the floor able to support the weight of the HPWH?

How is the system configured? Location of HPWH Semi-/Un-Conditioned 

Conditioned

Garage

Attic

HPWH Operation Mode Hybrid Mode

Heat Pump

Electric Resistance

Temperature Set Point 

(120 °F recommended) ______ o

F

Condensate Pump

Heat Trap

Mixing Valve

Maintenance How often should filter be 

cleaned? Every ______ Months

* Blanks to be filled out per manufacturer’s minimum specifications for model to be installed.
DOE/GO-102012-3456 ▪ February 2012

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.