WATER HEATER TEST PROCEDURE RULEMAKING: 

DEVELOPMENT TESTING PRELIMINARY REPORT 

ENERGY CONSERVATION PROGRAM FOR CONSUMER 

PRODUCTS AND CERTAIN INDUSTRIAL EQUIPMENT: 

Residential and Light Commercial Water Heaters 

November 2013 

U.S. Department of Energy 

Assistant Secretary 

Office of Energy Efficiency and Renewable Energy 

Building Technologies Program 

Appliances and Commercial Equipment Standards 

Washington, DC 20585
2

This Document was prepared for the Department of Energy 

by staff members of 

Navigant Consulting, Inc. and 

The National Institute of Standards and Technology 
3

WATER HEATER TEST PROCEDURE RULEMAKING:

DEVELOPMENT TESTING PRELIMINARY REPORT 

TABLE OF CONTENTS 

1. Introduction ............................................................................................................................. 6

1.1. Current Test Procedure ................................................................................................... 6

1.2. The Proposed Test Procedure ......................................................................................... 9

1.3. Tested Products ............................................................................................................. 11

2. Impact on First-Hour Rating of Storage Water Heaters ....................................................... 13

3. Impact on Maximum GPM Rating of Instantaneous Water Heaters .................................... 15

4. Impact on Energy Factor ....................................................................................................... 17

4.1. Storage Water Heaters .................................................................................................. 17

4.2. Instantaneous Water heaters ......................................................................................... 19

5. Effects of Proposed Test Procedure on Different Categories of Water Heater .................... 21

5.1. Storage Water Heaters .................................................................................................. 21

5.2. Instantaneous Water Heaters ......................................................................................... 22

6. Variance in Energy Factor Ratings for Water Heaters Under Different Draw Profiles ....... 23

6.1. By Water Heater Type .................................................................................................. 23

6.2. By Energy Source ......................................................................................................... 25

6.3. By Applicable Draw Profile.......................................................................................... 27

7. Summary ............................................................................................................................... 30
4

LIST OF TABLES

Table 1: 24-hour simulated use test draw profile criteria for storage water heaters ........................9

Table 2: 24-hour simulated use test draw profile criteria for instantaneous water heaters ..............9

Table 3: 24-hour simulated use test draw profiles for proposed test procedure ............................10

Table 4: Products used in residential water heater test report .......................................................11

Table 5: Averaged first-hour rating of storage water heaters under proposed test 

procedure as percentage of current first-hour rating, categorized by energy 

source and applicable draw profile ........................................................................21

Table 6: Averaged energy factor of storage water heaters under proposed test procedure 

as percentage of current energy factor, categorized by energy source and 

applicable draw profile ..........................................................................................21

Table 7: Averaged maximum gpm rating of instantaneous water heaters under proposed 

test procedure as percentage of current maximum gpm rating, categorized 

by energy source and applicable draw profile .......................................................22

Table 8: Averaged energy factor of instantaneous water heaters under proposed test 

procedure as percentage of current energy factor, categorized by energy 

source and applicable draw profile ........................................................................22

LIST OF FIGURES 

Figure 1: First-hour rating of storage water heaters under proposed test procedure as 

percentage of current first-hour rating, as function of current first-hour 

rating ......................................................................................................................13

Figure 2: First-hour rating of storage water heaters under proposed test procedure as 

percentage of current first-hour rating, as function of applicable draw 

profile .....................................................................................................................14

Figure 3: Maximum gpm rating of instantaneous heaters under proposed test procedure as 

percentage of current maximum gpm rating, as function of current 

maximum gpm rating .............................................................................................15

Figure 4: Maximum gpm rating of instantaneous water heaters under proposed test 

procedure as percentage of current maximum gpm rating, as function of 

draw profile established by the proposed maximum gpm rating test ....................16

Figure 5: Energy factor of storage water heaters under proposed test procedure as 

percentage of current energy factor, as function of current energy factor .............18

Figure 6: Energy factor of storage water heaters under proposed test procedure as 

percentage of current energy factor, as function of applicable draw profile .........18

Figure 7: Energy factor of instantaneous water heaters under proposed test procedure as 

percentage of current energy factor, as function of current energy factor .............19
5

Figure 8: Energy factor of instantaneous water heaters under proposed test procedure as 

percentage of current energy factor, as function of applicable draw profile .........20

Figure 9: Energy factor ratings of storage water heaters tested with different draw profiles 

(heat pump water heater S-HP-1 excluded) ...........................................................24

Figure 10: Energy factor ratings of storage heat pump water heater S-HP-1 tested with 

different draw profiles............................................................................................24

Figure 11: Energy factor ratings for instantaneous water heaters tested with different 

draw profiles ..........................................................................................................25

Figure 12: Energy factor ratings for water heaters using natural gas as an energy source ............26

Figure 13: Energy factor ratings for water heaters using oil as an energy source .........................26

Figure 14: Energy factor ratings for water heaters using electricity as an energy source .............27

Figure 15: Energy factor ratings for water heaters testing for point of use draw profile ..............28

Figure 16: Energy factor ratings for water heaters testing for low usage draw profile (heat 

pump water heater S-HP-1 excluded) ....................................................................28

Figure 17: Energy factor ratings for water heaters testing for medium usage draw profile ..........29

Figure 18: Energy factor ratings for water heaters testing for high usage draw profile ................29
6

WATER HEATER TEST PROCEDURE RULEMAKING:

DEVELOPMENT TESTING PRELIMINARY REPORT 

1. INTRODUCTION 

The American Energy Manufacturing and Technical Corrections Act (AEMTCA) requires DOE 

to establish a uniform efficiency descriptor for covered water heaters. (42 U.S.C. 6295(e)(5)) 

Consequently, the U.S. Department of Energy (DOE) initiated a rulemaking to consider 

amendments to its existing test procedures for covered residential and commercial water heaters. 

As part of this effort, DOE conducted a series of tests to assess the impact of proposed revisions 

and additions to the current DOE test procedures for residential water heaters and certain 

commercial water heaters. The purpose of the testing is to validate the proposed test method (78 

FR 66201) and examine the impact of the proposed test procedure revisions on the first-hour 

rating of storage water heaters, maximum gallons per minute rating of instantaneous water 

heaters, and energy factor of both storage and instantaneous water heaters. In addition, the test 

results were used to assess the variability in the energy factor based on the draw profile selected, 

as well as the impact of the proposed amendments on different types of water heaters. DOE 

collected and analyzed data on the energy factor, first hour rating (for storage water heaters), and 

maximum gallon per minute (max gpm, for instantaneous water heaters) of a number of different 

types of water heaters for this report, and considered the following impacts: 

 Impact of test procedure revisions and additions on first hour rating of residential storage 

water heaters 

 Impact on maximum gallon per minute of instantaneous water heaters 

 Impact on energy factor of all water heaters 

 Effects on different categories of water heater (e.g., gas-fired storage, electric storage, 

gas-fired instantaneous, etc.) 

 Variance in energy factor ratings of water heaters tested under different draw profiles 

(e.g., point of use, low usage, etc.) 

1.1. CURRENT TEST PROCEDURE

Residential Water Heaters 

The current DOE test procedure for residential water heaters (10 CFR 430, Subpart B, Appendix 

E) provides test protocols for storage water heaters to be tested for a first-hour and energy factor 

rating, and for instantaneous residential water heaters to be tested for a maximum gpm and 

energy factor rating. The first-hour rating test measures the volume of hot water that can be 

delivered by a storage water heater in a single hour, while the maximum gpm rating reflects the 

maximum flow rate at which an instantaneous water heater can continuously deliver hot water at 

a useful temperature. The energy factor rating test measures overall water heater efficiency 
7

(including active, standby, and cycling operation) over a 24-hour period at a specific set of rating 

conditions and single draw profile. 

Under current testing procedure, the ambient air temperature during all tests (first hour, max 

gpm, and energy factor) must be maintained between 65°F and 70°F, the inlet water temperature 

must be 58°F ± 2°F, and the thermostat must be adjusted to a setting that achieves a mean 

internal storage tank temperature of 135°F ± 5°F. 

For the first-hour rating test, the storage water heater is allowed to operate until it is at an 

average internal tank temperature of 135°F ± 5°F. Once the target tank temperature is achieved, 

the test begins and hot water is drawn at a rate of 3.0 gpm until the outlet temperature of the 

water exiting the storage tank decreases to 25°F less than the maximum observed outlet 

temperature. Subsequent draws begin when the thermostat acts to reduce the supply of heat 

energy to the storage tank and continue until the outlet temperature of the water exiting the 

storage tank decreases to 25°F less than the maximum observed outlet temperature for the given 

draw. This process is repeated for a total time of one hour. At the end of the hour, if a draw is in 

progress, that draw is allowed to complete normally (i.e., until the outlet temperature of water 

exiting the storage tank decreases to 25°F less than the maximum observed outlet temperature). 

If a draw is not occurring, a final draw is initiated and then terminated when the outlet water 

temperature reaches the same outlet temperature that the previous draw was terminated at. The 

first-hour rating is then calculated as the total volume of hot water drawn over this period (in 

gallons), and is a function of both the storage volume and water heater recovery rate. 

In the maximum gpm test, after the thermostat is adjusted to a set point that achieves an outlet 

temperature of 135°F ± 5°F, water is drawn from the instantaneous water heater for a total time 

of 10 minutes at the maximum possible flow rate while maintaining the target set point 

temperature. The maximum gpm rating is calculated as the total volume of water drawn over this 

period (in gallons) divided by ten minutes. 

The energy factor rating is determined from a 24-hour simulated use test. In this test a total of 

64.3 gallons of water are removed from the water heater at a rate of 3.0 gpm over six equal draw 

periods.a Initially, the water heater is operated at a set point that achieves an average internal 

temperature of 135°F ± 5°F for storage water heaters or provides an outlet temperature of 135°F 

± 5°F for instantaneous water heaters. At the start of the test, a volume of water equal to onesixth of 64.3 gallons is drawn. Another draw equal to one-sixth of 64.3 gallons is drawn at the 

start of the each subsequent hour and continues for a total of six draws. After the sixth draw, the 

water heater is left in standby mode until 24 hours have elapsed from the start of the test. The 

energy factor of the water heater is then calculated as the total energy contained in the delivered 

hot water divided by the total energy the water heater consumed during the 24-hour test period.

The energy factor is a function of several intermediate metrics, such as recovery efficiency and 

 

a

 If an instantaneous water heater cannot deliver water at 3.0 GPM and a temperature of 135°F±5°F, then the water 

flow rate is reduced such that the discharge temperature is 135°F±5°F and heater firing rate is maximized. 
8

standby loss, and is normalized for differences from the nominal test parameters that occur 

during testing.b

Commercial Water Heaters 

The current test procedure for commercial water heaters is specified at 10 CFR 431.106 and 

references the American National Standards Institute (ANSI) Z21.10.3-2011, “Gas Water 

Heaters, Volume III, Storage Water Heaters with Input Ratings above 75,000 Btu per Hour, 

Circulating and Instantaneous.” The DOE test procedure provides a method to determine the 

thermal efficiency and standby loss for gas-fired and oil-fired storage and instantaneous water 

heaters, and to determine the standby loss for electric storage and instantaneous water heaters. 

For determining thermal efficiency, the DOE test method requires that the thermostat first be 

adjusted so that the maximum mean tank temperature after cut-out is 140°F ± 5°F. Inlet water is 

supplied at 70°F ± 2°F and the ambient air temperature is maintained 75 °F ± 10°F. Water is 

drawn from the water heater and the flow rate of the water being drawn is adjusted until the 

temperature is a constant 70°F ± 2°F above the supply water temperature. Once the outlet 

temperature becomes constant, as determined by no variation in excess of more than 2°F over a 3 

minute period, the outlet water is diverted to a weighing container for exactly 30 minutes. Gas or 

oil and/or electrical consumption are metered over the 30 minute period, and the water is 

weighed at the end of the test. In addition, inlet and outlet water temperature measurements are 

recorded during the test, as well as the temperature, pressure, and heating value of the fuel and 

barometric pressure. Thermal efficiency is then calculated as the ratio of the energy in the 

delivered hot water to the total fossil fuel and electrical energy consumed during the test period. 

For determining standby loss, the DOE test method requires that the water heater be set up as 

described for the thermal efficiency test. The water heater is then put into operation and after the 

second cut-out the test begins. The test continues until either (1) the first cutout after 24 hours or 

(2) 48 hours if the water heater is not in the heating mode at that time, whichever happens first. 

Every 15 minutes during the test, the ambient air temperature and mean tank temperature are 

recorded, and at the end of the test the total fuel and/or electrical consumption is recorded. The 

standby loss (as a percent) is then calculated as the ratio of average hourly energy consumption 

to the heat content of the stored water above room temperature. For gas and oil water heaters, 

the standby loss percentage is then tabulated in Btu per hour. 

 

b

 Adjustments are made to account for the fact that the temperature difference between the storage tank and 

surrounding ambient air may not be the nominal 67.5°F due to the 10°F allowable variation in storage tank 

temperature (for storage water heaters) or discharge temperature (for instantaneous water heaters) and the 5°F 

allowable variation in ambient air temperature. Another adjustment is made to take into account that the temperature 

difference between the outlet and supply water may not be equivalent to the nominal value of 77°F due to tolerances 

in the inlet water temperature and allowable variation in the storage tank temperature (for storage water heaters) or 

discharge water temperature (for instantaneous water heaters). 
9

1.2. THE PROPOSED TEST PROCEDURE 

DOE has expanded the test procedure scope to include electric instantaneous water heaters, water 

heaters with between 2 and 20 gallons of storage volume, and gas-fired and oil-fired storage 

water heaters with storage volumes up to 120 gallons. The test method also covers certain 

commercial equipment that meet the definition of “light commercial” water heaters proposed in 

the notice of proposed rulemaking. Additionally, the proposed DOE method would lower the set 

point temperature to 125°F, rather than 135°F, while requiring water flow rates to vary for each 

draw during the 24-hour simulated use test. Test conditions for inlet water and ambient air 

temperature are still prescribed as 58°F and 67.5°F, respectively. 

For storage water heaters, the proposed first-hour rating test is generally conducted in the same 

manner as the current test procedure, but the target set point temperature is now 125°F and water 

draws are terminated when the outlet water temperature drops 15°F from its maximum value 

instead of 25°F. In addition, the result of the first-hour rating is then used to select the draw 

pattern used for the 24-hour simulated use test, summarized in Table 1 below.

Table 1: 24-hour simulated use test draw profile criteria for storage water heaters 

First hour rating greater than or 

equal to:

... And First Hour Rating less 

than...

Draw pattern to be used in 24-hour 

simulated use test

0 gal 20 Point of use

20 55 Low usage

55 80 Medium usage

80 No limit High usage

For instantaneous water heaters, the proposed maximum gpm rating test is generally the same as 

the current test, except for the decrease in water discharge temperature from 135°F to 125°F.c As 

in the first-hour rating test for storage water heaters, the result of the maximum gpm test is now 

used to select the draw pattern for the 24-hour simulated use test, summarized in Table 2 below.

Table 2: 24-hour simulated use test draw profile criteria for instantaneous water heaters 

Max GPM rating greater than or 

equal to:

... And max GPM rating less 

than...

Draw pattern to be used in 24-hour 

simulated use test

0 GPM 1.7 Point of use

1.7 2.8 Low usage

2.8 4.0 Medium usage

4.0 No limit High usage

 

c

 Under the proposed test, if an instantaneous water heater cannot deliver water at 2.0 GPM and 125°F ± 5°F, then 

its flow rate is reduced such that the discharge temperature is 125°F ± 5°F and its heater firing rate is maximized. 
10

Based on the performance of the storage water heater in the first-hour rating test or the 

instantaneous water heater in the maximum gpm test, the unit is classified into one of four 

categories to reflect its expected use in the field–point of use, low usage, medium usage, and 

high usage. Each category is subject to a unique draw profile, summarized in Table 3.

Table 3: 24-hour simulated use test draw profiles for proposed test procedure 

1. Point of Use Draw Pattern

Draw 

Number

Time During 

Test 

(hh:mm)

Volume 

(gallons)

Flow 

Rate 

(GPM)

1* 0:00 2.0 (7.6) 1 (3.8)

2* 1:00 1.0 (3.8) 1 (3.8)

3* 1:05 0.5 (1.9) 1 (3.8)

4* 1:10 0.5 (1.9) 1 (3.8)

5* 1:15 0.5 (1.9) 1 (3.8)

6 8:00 1.0 (3.8) 1 (3.8)

7 8:15 2.0 (7.6) 1 (3.8)

8 9:00 1.5 (5.7) 1 (3.8)

9 9:15 1.0 (3.8) 1 (3.8)

Total Volume Drawn Per Day: 10 gallons (38 L)

* Denotes draws in first draw cluster. 

2. Low Usage Draw Pattern

Draw 

Number

Time During 

Test 

(hh:mm)

Volume 

(gallons)

Flow 

Rate 

(GPM)

1* 0:00 15.0 (56.8) 1.7 (6.5)

2* 0:30 2.0 (7.6) 1 (3.8)

3* 1:00 1.0 (3.8) 1 (3.8)

4 10:30 6.0 (22.7) 1.7 (6.5)

5 11:30 4.0 (15.1) 1.7 (6.5)

6 12:00 1.0 (3.8) 1 (3.8)

7 12:45 1.0 (3.8) 1 (3.8)

8 12:50 1.0 (3.8) 1 (3.8)

9 16:15 2.0 (7.6) 1 (3.8)

10 16:45 2.0 (7.6) 1.7 (6.5)

11 17:00 3.0 (11.4) 1.7 (6.5)

Total Volume Drawn Per Day: 38 gallons (144 L) 

* Denotes draws in first draw cluster. 

3. Medium Usage Draw Pattern

Draw 

Number

Time 

During Test 

(hh:mm)

Volume 

(gallons)

Flow 

Rate 

(GPM)

1* 0:00 15.0 (56.8) 1.7 (6.5)

2* 0:30 2.0 (7.6) 1 (3.8)

3* 1:40 9.0 (34.1) 1.7 (6.5)

4 10:30 9.0 (34.1) 1.7 (6.5)

5 11:30 5.0 (18.9) 1.7 (6.5)

6 12:00 1.0 (3.8) 1 (3.8)

7 12:45 1.0 (3.8) 1 (3.8)

8 12:50 1.0 (3.8) 1 (3.8)

9 16:00 1.0 (3.8) 1 (3.8)

10 16:15 2.0 (7.6) 1 (3.8)

11 16:45 2.0 (7.6) 1.7 (6.5)

12 17:00 7.0 (26.5) 1.7 (6.5)

Total Volume Drawn Per Day: 55 gallons (208 L)

* Denotes draws in first draw cluster. 

4. High Usage Draw Pattern

Draw 

Number

Time 

During Test 

(hh:mm)

Volume 

(gallons)

Flow 

Rate 

(GPM)

1* 0:00 27.0 (102) 3 (11.4)

2* 0:30 2.0 (7.6) 1 (3.8)

3* 0:40 1.0 (3.8) 1 (3.8)

4* 1:40 9.0 (34.1) 1.7 (6.5)

5 10:30 15.0 (56.8) 3 (11.4)

6 11:30 5.0 (18.9) 1.7 (6.5)

7 12:00 1.0 (3.8) 1 (3.8)

8 12:45 1.0 (3.8) 1 (3.8)

9 12:50 1.0 (3.8) 1 (3.8)

10 16:00 2.0 (7.6) 1 (3.8)

11 16:15 2.0 (7.6) 1 (3.8)

12 16:30 2.0 (7.6) 1.7 (6.5)

13 16:45 2.0 (7.6) 1.7 (6.5)

14 17:00 14.0 (53.0) 3 (11.4)

Total Volume Drawn Per Day: 84 gallons (318 L)

* Denotes draws in first draw cluster. 
11

As with the current test method, the energy factor of the water heater is calculated as the total 

heat energy of delivered water divided by the total energy the water heater consumes throughout 

the 24-hour simulated use test. Energy consumption rates are also modified to take into account 

that the difference between storage tank and ambient temperature may not be the nominal 

57.5°F, and the difference between inlet and outlet water temperature may not be the nominal 

value of 67°F. 

1.3. TESTED PRODUCTS 

To validate the proposed test method and explore the impacts of the proposed test procedure on 

first-hour rating, DOE tested fifteen storage water heaters and six instantaneous water heaters. 

Table 4 lists the twenty-one units along with their relevant attributes used in this analysis. 

Table 4: Products used in residential water heater test report 

Water 

Heater ID

Heater 

Type

Energy 

Source

Rated Storage 

Volume (gal)

Rated Input Notes

S-NG-1 Storage Natural 

gas

40 40 kBtu/h

S-NG-2 Storage Natural 

gas

29 60 kBtu/h

S-NG-3 Storage Natural 

gas

75 70 kBtu/h

S-NG-4 Storage Natural 

gas

40 40 kBtu/h

S-NG-5 Storage Natural 

gas

40 40 kBtu/h

S-O-1 Storage Oil 32 104 kBtu/h

S-O-2 Storage Oil 32 104 kBtu/h

S-E-1 Storage Electric 30 4.5 kW

S-E-2 Storage Electric 50 4.5 kW

S-E-3 Storage Electric 80 4.5 kW

S-E-4 Storage Electric 4 1.5 kW Not covered by the current 

DOE test procedure

S-E-5 Storage Electric 6 2 kW Not covered by the current 

DOE test procedure

S-E-6 Storage Electric 2.75 1.5 kW Not covered by the current 

DOE test procedure
12

S-E-7 Storage Electric 80 4.5 kW

S-HP-1 Storage Heat 

pump*

50 4.5 kW

I-NG-1 Instantaneo

us

Natural 

gas

0 199 kBtu/h

I-NG-2 Instantaneo

us

Natural 

gas**

0 150 kBtu/h

I-NG-3 Instantaneo

us

Natural 

gas

0 175 kBtu/h

I-E-1 Instantaneo

us

Electric 0 3.5 kW

I-E-2 Instantaneo

us

Electric 0 12 kW

I-E-3 Instantaneo

us

Electric 0 28.8 kW Not covered by the current 

DOE test procedure

* Water heater S-HP-1 is electric- and heat pump-powered, and includes storage tank. 

** Note that propane gas is an alternative energy source for water heater I-NG-2. 
13

2. IMPACT ON FIRST-HOUR RATING OF STORAGE WATER HEATERS 

DOE tested fifteen storage water heaters for first hour rating under the proposed amended test 

procedure, including five natural gas-fired, two oil-fired, seven electric resistance-powered, and 

one heat pump-powered. For the twelve storage water heater models that are covered by the 

current DOE test procedure, DOE compared the measured first-hour ratings under the existing 

test procedure to the first hour ratings observed under the proposed revised test procedure, as 

shown in Figure 1 below.d

 Five out of the twelve saw their first-hour rating decrease from the 

current to the proposed test procedure, while the remaining seven water heaters saw their firsthour rating increase. On average, storage water heater measured first-hour ratings under the 

proposed test procedure are 103% of their current measured value. From Figure 1 below, the 

majority of water heaters see their measured first-hour rating change to between approximately 

90% and 110% of their measured rating under the current test method. 

Figure 1: First-hour rating of storage water heaters under proposed test procedure as 

percentage of current first-hour rating, as function of current first-hour rating 

DOE also investigated the change in measured first-hour rating of water heaters in different draw 

profile categories. Figure 2 below categorizes the twelve applicable storage water heaters into 

their corresponding draw profile based on first-hour rating test results under the proposed test 

procedure. It appears from Figure 2 that the measured first-hour rating of high usage water 

heaters increases from the current to proposed test procedure, while low usage and medium 

usage water heaters see their measured first-hour rating either drop or remain relatively constant. 

 

d

 Water heaters S-E-4, S-E-5, and S-E-6 do not have current first-hour or energy factor ratings since they have a 

storage volume between 2 and 20 gallons, and fall in a category not currently addressed by the DOE test procedure. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 20 40 60 80 100 120 140 160 180

First-hour rating under new test procedure as 

percentage of rating under current test

First-hour rating under current test procedure 

Natural gas Oil Electric Heat pump Line of equivalence
14

Figure 2: First-hour rating of storage water heaters under proposed test procedure as 

percentage of current first-hour rating, as function of applicable draw profile 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.0 1.0 2.0 3.0 4.0

First-hour rating under new test procedure as 

percentage of rating under current test

Applicable draw profile under new test procedure

Natural gas Oil Electric Heat pump Line of equivalence

Point of use Low usage Medium usage High usage
15

3. IMPACT ON MAXIMUM GPM RATING OF INSTANTANEOUS WATER 

HEATERS 

To determine the impact of the differences between the current and the proposed test procedures 

on the measured max gpm, DOE tested six instantaneous water heaters including three natural 

gas-powered and three electric-powered. Although one of the electric water heaters (I-E-3) is 

currently outside of the scope of the DOE test method for residential water heaters, DOE was 

able to perform the current max gpm test on that water heater without modification, and as such, 

included that unit in the comparison between the current and proposed test method.eSimilar to 

the analysis of first-hour ratings of storage water heaters in Section 2, DOE compared the change 

in measured maximum gpm of instantaneous water heaters under the proposed test procedure to 

the measured maximum gpm under the current test procedure. Figure 3 below plots the measured 

maximum gpm under the proposed test procedure as a percentage of the measured maximum 

gpm under the current test procedure. From this figure, the three electric instantaneous water 

heaters saw an increase in their measured maximum gpm rating of 14% on average, while the 

three natural gas instantaneous water heaters saw an increase of 13%.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 1 2 3 4 5 6 Maximum GPM rating under new test procedure as percentage of rating under current test 

Maximum gpm rating under current test procedure

Natural gas Electric Line of equivalence

Figure 3: Maximum gpm rating of instantaneous heaters under proposed test procedure as 

percentage of current maximum gpm rating, as function of current maximum gpm rating 

The instantaneous water heaters observed in this study are also categorized into their applicable 

draw pattern based on maximum gpm test results. The measured maximum gpm under the 

 

e

 The unit I-E-3 would be covered under the proposed revised test method. 
16

proposed test procedure as a percentage of the measured maximum gpm under the current test 

procedure is plotted as a function of the draw profile in Figure 4 below. As expected, the 

measured maximum gpm of instantaneous water heaters increases as the set point temperature 

drops from 135°F to 125°F from the current to proposed test procedure. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.0 1.0 2.0 3.0 4.0

Maximum GPM rating under new test 

procedure as percentage of ating under current test 

Applicable draw profile under current test procedure

Natural gas Electric Line of equivalence

Point of use Low usage Medium usage High usage

Figure 4: Maximum gpm rating of instantaneous water heaters under proposed test 

procedure as percentage of current maximum gpm rating, as function of draw profile 

established by the proposed maximum gpm rating test 
17

4. IMPACT ON ENERGY FACTOR 

DOE investigated the impact of the proposed test procedure on the energy factor of both storage 

and instantaneous water heaters. Based on the performance of the water heater in the proposed

first-hour rating or maximum gpm test (as shown in Sections 2 and 3), DOE subjected each 

water heater to the appropriate draw profile as specified by the proposed test method . DOE also 

subjected each water heater to at least one other draw profile to better understand how the energy 

factor of a specific water heater model varies across different draw profiles, the analysis of which 

is presented in Section 6. The additional draw profile(s) tested were the pattern directly above 

and/or below the nominal usage pattern that the unit would qualify for. For example, if a unit 

qualified for the high usage pattern based on its first hour rating, it was also tested using the 

medium usage pattern. In several cases, DOE performed additional experimental testing at draw 

patterns two levels above the nominal pattern (e.g., for a unit with a low usage nominal pattern, 

DOE also performed testing at the high usage pattern) to analyze the trend in the impact on 

measured energy factor across multiple draw patterns.f

4.1. STORAGE WATER HEATERS

The impact of the differences between the current and proposed test procedure on the measured 

energy factor was examined for all twelve of the storage water heaters to which the current test 

procedure is applicable.g As shown in Figure 5 below, the measured energy factor of six of the 

twelve storage water heaters increased under the proposed test method, while the measured 

energy factor of five water heaters decreased and one stayed constant. 

Results for storage water heaters are also categorized by their applicable draw profile identified 

using the measured first-hour rating under the proposed test procedure. From Figure 6, all water 

heaters subject to a low or medium usage draw profile experience a decrease in measured energy 

factor, while the majority of those water heaters subject to a high usage draw profile experience 

an increase in measured energy factor. This is to be expected, as the energy factor of storage 

water heaters is correlated to the total volume drawn from the 24-hour simulated use test. Since 

the high usage test under the proposed procedure draws a higher total volume of water than the 

current test procedure, one would expect the energy factor to rise. Conversely, the low and 

medium usage tests under the proposed procedure draw less water than required by the current 

test method, and one would expect their energy factors to fall. 

 

f Additionally, some water heaters were originally grouped into different draw profile bins than they are currently. 

This is because DOE adjusted the draw profile first-hour and maximum gpm limits after analyzing data made 

available mid-testing. Thus, more energy factor ratings were produced than necessary for some water heaters. For 

example, water heater S-NG-2 was tested under low, medium, and high usage draw patterns even though it currently 

qualifies for the high usage test, since it originally qualified for the medium usage test before DOE adjustments.

g This analysis excludes the change in energy factor for water heaters S-E-4, S-E-5, and S-E-6 since their small 

storage volumes (greater than 2 and less than 20 gallons) limit them to point of use applications and cannot be 

appropriately tested under the current test procedure.
18

Figure 5: Energy factor of storage water heaters under proposed test procedure as 

percentage of current energy factor, as function of current energy factor 

Figure 6: Energy factor of storage water heaters under proposed test procedure as 

percentage of current energy factor, as function of applicable draw profile 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

Energy factor under new test procedure as 

0 0.5 1 1.5 2 2.5

percentage of energy factor under current test

Energy factor rating under current test procedure

Natural gas Oil Electric Heat pump Line of equivalence

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.0 1.0 2.0 3.0 4.0

Energy factor under new test procedure as 

percentage of energy factor under current test

Applicable draw profile under new test procedure

Natural gas Oil Electric Heat pump Line of equivalence

Point of use Low usage Medium usage High usage
19

4.2. INSTANTANEOUS WATER HEATERS 

The change in energy factor for instantaneous water heaters due to the differences between the 

current and proposed test procedures is evaluated for the six available instantaneous water 

heaters. As noted previously, one of the instantaneous water heaters tested (I-E-3) is outside of 

the scope of the current test method. However, since the current test method could be run on that 

unit without modification, and since the unit is covered by the proposed revised test method, 

DOE included that unit for comparison. Two of the three gas-fired instantaneous water heaters 

saw a slight increase in their measured energy factor under the proposed test procedure, while all 

three electric-powered instantaneous water heaters saw a decrease, as shown in Figure 7. When 

isolated by applicable draw pattern in Figure 8 the results are more easily assessed, as the point 

of use water heater category shows a clearer decrease in measured energy factor than the low, 

medium, and high usage categories, which tend to instead stay relatively constant from the 

current to proposed test procedure. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 0.2 0.4 0.6 0.8 1 1.2

Energy factor under new test procedure as 

percentage of energy factor under current test

Energy factor rating under current test procedure

Natural gas Electric Line of equivalence

Figure 7: Energy factor of instantaneous water heaters under proposed test procedure as 

percentage of current energy factor, as function of current energy factor 
20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Energy factor under new test procedure as 

0.0 1.0 2.0 3.0 4.0

percentage of energy factor under current test 

Applicable draw profile under current test procedure

Natural gas Electric Line of equivalence

Point of use Low usage Medium usage High usage

Figure 8: Energy factor of instantaneous water heaters under proposed test procedure as 

percentage of current energy factor, as function of applicable draw profile 
21

5. EFFECTS OF PROPOSED TEST PROCEDURE ON DIFFERENT CATEGORIES 

OF WATER HEATER 

Since DOE expects the proposed changes in the test method to likely affect different categories 

of water heaters in different ways, DOE is presenting the average change in first-hour, maximum 

gpm, and energy factor ratings separately by type, applicable draw profile, and energy source. 

5.1. STORAGE WATER HEATERS 

Table 5 below shows the average change in measured first-hour rating of the twelve storage 

water heaters evaluated. The measured first-hour ratings for storage water heaters on average 

increased by 3%, with water heaters tested under the high usage draw pattern experiencing the 

most significant increase in measured first-hour rating and water heaters tested under the low 

usage draw pattern experiencing the most significant decrease. 

Table 5: Averaged first-hour rating of storage water heaters under proposed test 

procedure as percentage of current first-hour rating, categorized by energy source and 

applicable draw profile 

Natural gas Oil Electric Heat pump All

Point of use N/A N/A N/A N/A N/A

Low usage N/A N/A 105% 87% 96%

Medium usage 98% N/A 98% N/A 98%

High usage 111% 108% 101% N/A 107%

All 106% 108% 101% 87% 103%

First-Hour Rating by Energy Source Draw Profile

The average change in measured energy factor for the twelve storage water heaters is shown in 

Table 6 below. On average, the measured energy factor of water heaters tested under the high 

usage draw pattern increased by 8%, while water heaters tested under the medium and low usage 

draw patterns decreased by 4% and 11% on average, respectively. Again, this is expected as the 

energy factor is correlated to the total volume drawn during the 24-hour simulated use test for 

storage water heaters. 

Table 6: Averaged energy factor of storage water heaters under proposed test procedure as 

percentage of current energy factor, categorized by energy source and applicable draw 

profile 

Natural gas Oil Electric Heat pump All

Point of use N/A N/A N/A N/A N/A

Low usage N/A N/A 90% 89% 89%

Medium usage 94% N/A 100% N/A 96%

High usage 113% 98% 111% N/A 108%

All 107% 98% 100% 89% 102%

Energy Factor by Energy Source Draw Profile
22

5.2. INSTANTANEOUS WATER HEATERS 

Table 7 below shows the average change in the measured maximum gpm rating of instantaneous 

water heaters for different categories of applicable draw profile and energy source. The point of 

use and low usage electric categories saw increases of 14% and 13% on average for the 

measured maximum gpm, respectively, while the medium and high usage natural gas categories 

saw increases in measured maximum gpm of 14% and 9%, respectively. 

Table 7: Averaged maximum gpm rating of instantaneous water heaters under proposed 

test procedure as percentage of current maximum gpm rating, categorized by energy 

source and applicable draw profile 

Natural gas Electric All

Point of use N/A 114% 114%

Low usage N/A 113% 113%

Medium usage 114% N/A 114%

High usage 109% N/A 109%

Draw Profile

All 113% 114% 113%

Maximum GPM Rating by Energy Source

The average change in energy factor for instantaneous water heaters is shown in Table 8 below. 

The electric point of use, electric low usage, and natural gas medium usage categories experience 

decreases in energy factor of 23%, 4%, and 2% on average, respectively. The natural gas high 

usage category experienced a 3% increase in its energy factor, on average. 

Table 8: Averaged energy factor of instantaneous water heaters under proposed test 

procedure as percentage of current energy factor, categorized by energy source and 

applicable draw profile 

Natural gas Electric All

Point of use N/A 77% 77%

Low usage N/A 96% 96%

Medium usage 98% N/A 98%

High usage 103% N/A 103%

All 100% 83% 91%

Energy Factor by Energy Source

Draw Profile
23

6. VARIANCE IN ENERGY FACTOR RATINGS FOR WATER HEATERS UNDER 

DIFFERENT DRAW PROFILES

The water heaters tested by DOE in this report were subjected to at least one other draw profile 

that did not match its applicable draw pattern prescribed by the proposed test procedure based on 

the tested first hour rating (storage water heaters) or maximum gpm rating (instantaneous water 

heaters). As explained above, the additional draw profile(s) tested were the pattern(s) directly 

above and/or below the nominal usage pattern that the unit would qualify for. This allowed DOE 

to evaluate how different 24-hour simulated use test draw patterns affect the performance of 

different categories of water heaters. In this section, the variance in measured energy factor for 

water heaters tested under different draw profiles is observed for appropriate water heater 

categories. These include water heater type, energy source, and applicable draw pattern. 

6.1. BY WATER HEATER TYPE 

The observed water heater energy factor under the proposed test procedure is filtered by storage 

water heaters in Figure 9 and by instantaneous water heaters in Figure 11. Additionally, Figure 

10 shows the energy factor ratings of the storage heat pump water heater S-HP-1 under different 

draw profiles in a separate chart, since its energy factor is so much greater than normal heat 

pump water heaters that it would make trends observed in Figure 9 less obvious. From Figure 9

and Figure 10 below, the measured energy factor of storage water heaters (including heat pump 

water heater S-HP-1) increases as the draw profile moves from point of use through high usage. 

From Figure 11, the measured energy factor of instantaneous water heaters appears to follow a 

similar trend as storage water heaters, though potentially experiences a plateau from the low 

through high usage draw profiles. 
24

Figure 9: Energy factor ratings of storage water heaters tested with different draw profiles 

(heat pump water heater S-HP-1 excluded) 

Figure 10: Energy factor ratings of storage heat pump water heater S-HP-1 tested with 

different draw profiles 

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Medium usage High usage

Energy factor

Draw profile

S-NG-1 S-NG-2 S-NG-3 S-NG-4 S-NG-5 S-O-1 S-O-2

S-E-1 S-E-2 S-E-3 S-E-4 S-E-5 S-E-6 S-E-7

0

0.5

1

1.5

2

2.5

3

POU Low usage Med. usage High usage

Energy factor

Draw Profile

S-HP-1
25

0

0.2

0.4

0.6

0.8

1

1.2

Point of use Low usage Medium usage High usage

Energy factor

Draw profile

I-NG-1 I-NG-2 I-NG-3 I-E-1 I-E-2 I-E-3

Figure 11: Energy factor ratings for instantaneous water heaters tested with different draw 

profiles 

6.2. BY ENERGY SOURCE 

Changes in the measured energy factor of water heaters were then filtered by energy source. 

Figure 12 below isolates the change in the measured energy factor by natural gas-powered water 

heaters, and shows an increase in the measured energy factor from low through high usage draw 

profiles, as expected. Figure 13 and Figure 14 filter by oil-fired and electric water heaters, 

respectively, and show a similar trend as natural gas-fired water heaters.hThe same increasing 

trend is observed when isolating for the heat pump water heater S-HP-1, as shown previously in 

Figure 10 above. 

 

h The oil-fired water heater sample only contains storage water heaters since no oil-fired instantaneous water heaters 

were tested.
26

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Med. usage High usage

Energy factor

Draw profile

S-NG-1 S-NG-2 S-NG-3 S-NG-4 S-NG-5 I-NG-1 I-NG-2 I-NG-3

Figure 12: Energy factor ratings for water heaters using natural gas as an energy source 

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

POU Low usage Med. usage High usage

Energy factor

Draw profile

S-O-1 S-O-2

Figure 13: Energy factor ratings for water heaters using oil as an energy source 
27

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Med. usage High usage

Energy factor

Draw profile

S-E-1 S-E-2 S-E-3 S-E-4 S-E-5

S-E-6 S-E-7 I-E-1 I-E-2 I-E-3

Figure 14: Energy factor ratings for water heaters using electricity as an energy source 

6.3. BY APPLICABLE DRAW PROFILE 

Lastly, changes in the measured energy factor for water heaters were filtered by applicable draw 

profile – that is, the specific draw profile that the water heater qualified for given its performance 

in the first-hour or maximum gpm rating test. For example, Figure 15 plots the five water heaters 

that qualified for the point of use draw profile, yet were also tested under low usage draw profile 

conditions. In this figure, all five water heaters see significant increases in their measured energy 

factor when placed under the low usage draw profile. Figure 16 filters for water heaters that 

qualified for the low usage test, showing a marginal increase from point of use to low usage and 

from low to medium usage.i In addition, the heat pump (S-HP-1) water heater was also tested at 

the high usage pattern and shows a significant increase from medium to high usage, as observed 

in Figure 9 shown previously. Figure 17 filters by medium usage, and shows five water heaters 

that experience relatively marginal gains in measured energy factor. Figure 18 filters by high 

usage, and shows an obvious increase in measured energy factor. 

 

i

 Although the heat pump water heater S-HP-1 also qualified for the low usage draw profile, it is not included in 

Figure 16 since its energy factor ratings are so high that they would make trends observed for other water heaters 

less obvious. The energy factor ratings of the heat pump water heater at different draw profiles are instead available 

in Figure 9 above. 
28

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Med. usage High usage

Energy factor

Draw profile

I-E-1 I-E-2 S-E-4 S-E-5 S-E-6

Figure 15: Energy factor ratings for water heaters testing for point of use draw profile 

Figure 16: Energy factor ratings for water heaters testing for low usage draw profile (heat 

pump water heater S-HP-1 excluded) 

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Med. usage High usage

Energy factor

Draw Profile

I-E-3 S-E-1
29

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

POU Low usage Med. usage High usage

Energy factor

Draw profile

I-NG-2 I-NG-3 S-E-2 S-NG-1 S-NG-5

Figure 17: Energy factor ratings for water heaters testing for medium usage draw profile 

0

0.2

0.4

0.6

0.8

1

1.2

POU Low usage Med. usage High usage

Energy factor

Draw profile

I-NG-1 S-E-3 S-E-7 S-NG-2 S-NG-3 S-NG-4 S-O-1 S-O-2

Figure 18: Energy factor ratings for water heaters testing for high usage draw profile 
30

7. SUMMARY 

This report provides a preliminary assessment of the impact of proposed additions and revisions 

to the current test procedure for residential water heaters. These additions and revisions also 

apply to light commercial water heaters, which are defined as a new category of water heater in 

the notice of proposed rulemaking. Specifically, the impacts analyzed for this report include: 

 Impact of proposed test procedure revisions on measured first hour rating of storage 

water heaters, maximum gallon per minute of instantaneous water heaters, and energy 

factor of storage and instantaneous water heaters 

 Effects of the proposed test procedure revisions on different categories of water heater 

 Variance in measured energy factor ratings of units tested under different draw profiles 

Twenty-one water heaters were tested under the proposed test procedure, including fifteen 

storage and six instantaneous water heaters. The energy factor and first hour rating tests specified 

by the current test procedure are not applicable for three small storage water heaters, labeled in 

this study as S-E-4, S-E-5, and S-E-6, and thus comparisons between their measured energy 

factors under the current test procedure and the proposed test procedure cannot be made. 

For storage water heaters, DOE found that the measured first-hour rating under the proposed test 

procedure varied between 87 and 130% of the measured first-hour rating under the current test, 

with an average of 103%. The energy factor measured under the proposed test procedure as 

compared to that measured under the current test procedure varied by 89 to 128%, with an 

average of 102%. For instantaneous water heaters, DOE found that the maximum gpm rating 

under the proposed test procedure varied between 109 and 117% of the current rating, with an 

average of 113%. The energy factor measured by the proposed test procedure as compared to 

that measured under the current test procedure varied by 74 to 103%, with an average of 91%.

This report also analyzed effects of the proposed test procedure revisions on different categories 

of water heater. The type of water heater most affected by the change in test procedure as 

observed in this study was the instantaneous, electric, water heater that would be tested using the 

point of use draw pattern, which saw an average energy factor rating of 77% the current value. 

The majority of other water heaters had measured energy factor ratings of 90 to 110% of the 

measured energy factor under the current test method.

Lastly, this report evaluated how water heaters assigned to their nominal draw profile behaved 

when subject to different draw profiles. It was found in all cases that as the total volume of water 

drawn during the 24-hour simulated use test increased—that is, the draw profile increased from 

point of use through high usage—the measured energy factor of the water heater also increased. 

Different categories of water heaters experienced steeper climbs in energy factor from one test to 

another, the greatest being storage water heaters from medium to high usage, and both storage 

and instantaneous water heaters from point of use to low usage. 

DOE will continue to conduct additional tests in order to better understand how the proposed test 

procedure affects the measured first-hour, maximum gpm, and energy factor ratings as compared 

to the values measured under the current test.