7-i

CHAPTER 7. ENERGY AND WATER USE DETERMINATION

TABLE OF CONTENTS

7.1 INTRODUCTION ...............................................................................................................1

7.2 PER-CYCLE ENERGY AND WATER CONSUMPTION BY EFFICIENCY 

LEVEL.................................................................................................................................1

7.3 AVERAGE ANNUAL ENERGY AND WATER CONSUMPTION BY 

EFFICIENCY LEVEL.........................................................................................................6

7.4 VARIABILITY IN ANNUAL ENERGY AND WATER CONSUMPTION: 

WASHER CAPACITY AND USAGE TRENDS ...............................................................8

LIST OF TABLES

Table 7.2.1 Top-loading Standard-Capacity Residential Clothes Washers: Per-Cycle 

Energy and Water Use by Efficiency Level ............................................................4

Table 7.2.2 Front-loading Standard-Capacity Residential Clothes Washers: Per-Cycle 

Energy and Water Use by Efficiency Level ............................................................5

Table 7.2.3 Top-loading Compact Residential Clothes Washers: Per-Cycle Energy and 

Water Use by Efficiency Level................................................................................5

Table 7.2.4 Front-loading Compact Residential Clothes Washers: Per-Cycle Energy 

and Water Use by Efficiency Level.........................................................................5

Table 7.3.1 Top-loading Standard-Capacity Residential Clothes Washers: Annual 

Energy and Water Use by Efficiency Level ............................................................7

Table 7.3.2 Front-loading Standard-Capacity Residential Clothes Washers: Annual 

Energy and Water Use by Efficiency Level ............................................................7

Table 7.3.4 Top-loading Compact Residential Clothes Washers: Annual Energy and 

Water Use by Efficiency Level................................................................................8

Table 7.3.3 Front-loading Compact Residential Clothes Washers: Annual Energy and 

Water Use by Efficiency Level................................................................................8

LIST OF FIGURES

Figure 7.4.1 Trends in Washer Usage and Capacity ....................................................................9

Figure 7.4.2 Annual Usage Distribution for Top-Loading Clothes Washers.............................10

Figure 7.4.3 Annual Usage Distribution for Front-Loading Clothes Washers ..........................10

Figure 7.4.4 Dryer usage for Households with Top-loading Clothes Washers..........................11

Figure 7.4.5 Dryer usage for Households with Front-loading Clothes Washers .......................12
7-1

CHAPTER 7. ENERGY AND WATER USE DETERMINATION

7.1 INTRODUCTION

To perform the life-cycle cost (LCC) and payback period (PBP) calculations described in 

Chapter 8, DOE had to determine the savings in operating costs that consumers would derive 

from higher efficiency standards for clothes washers. DOE used consumer energy and water use 

data, along with energy and water prices, to develop the most significant component of consumer 

operating costs in the LCC and PBP analyses*. This chapter describes how DOE established the

annual energy and water consumption of residential clothes washers.

7.2 PER-CYCLE ENERGY AND WATER CONSUMPTION BY EFFICIENCY 

LEVEL

DOE establishes the annual energy and water consumption of clothes washers by 

multiplying the per-cycle energy and water use by the number of cycles per year. The per-cycle 

energy consumption associated with a given clothes washer has three components: energy used 

for heating the water, operating the machine, and drying the clothes. DOE adopted test 

procedures for clothes washers in a final rule published on October 18, 2005.1That DOE test 

procedure provides the following equations to calculate total per-cycle energy consumption of 

clothes washers.

T E

T

CYCLE ME D

e

HE CW   

Where: 

CWCYCLE = total (without off-mode energy use) per-cycle energy consumption of 

clothes washer,

HET = per-cycle energy consumption for heating water [kilowatt-hours 

(kWh)/cycle)],

e = efficiency of electric water heater (100%) or gas water heater (75%),

MET = per-cycle machine energy consumption for operating washer (kWh/cycle), 

and

DE = per-cycle energy consumption for removing moisture from test load [i.e., 

dryer energy consumption (kWh/cycle)].

The following equation from the current DOE test procedure calculates the per-cycle 

energy consumption for removing moisture:

 

* Maintenance and repair costs are the other contributors.
7-2

DE LUF W  LUFavgWavg LUF W RMC 4%DEF DUF _

max max min min

Where:

LUF = load usage factor, 

W = weight of test load [pounds (lb)/cycle],

RMC = moisture content that remains after washing (lb),

DEF = nominal energy required for a clothes dryer to remove moisture from clothes 

(0.5kWh/lb), and

DUF = dryer usage factor, a percentage of washer loads dried in a clothes dryer (0.91).

For clothes washers with manual fill control systems, only the LUFmax and LUFmin terms 

are used. For clothes washers with adaptive fill control systems, all three terms are included. The 

values of W and LUF can be found in the current test procedure.

When considering gas drying, DOE multiplies the dryer energy consumption by a gas 

correction factor to account for the additional energy a gas dryer requires relative to an electric 

dryer. The following equation determines per-cycle energy consumption for gas drying.

DG = GCF × DE

Where:

DG = per-cycle energy consumption for gas dryer to remove moisture from test 

load, i.e., dryer energy consumption (kWh/cycle), and

GCF = gas correction factor = 1.12.2

DOE previously used a modified energy factor (MEF) and a water factor (WF) to 

establish the energy and water efficiencies of clothes washers. The following equations 

determine the MEF and WF:

CWCYCLE

C

MEF =

C

Q

WF T=

Where:

C = container capacity [cubic feet (cu ft)], and

QT = per-cycle water consumption for cold wash/cold/rinse [gallons (gal)/cycle].
7-3

The previous test procedure was revised to include non-active mode energy use.3This 

analysis takes those revisions into account by using the revised integrated energy and water 

factors defined below. 

IMEF = C / (CWcycle +cyclic off-mode energy)

The cyclic off-mode energy is expressed in units of kWh/cycle and obtained by dividing 

the annual off-mode energy use by the number of wash cycles per year. 

The integrated water factor is defined below.

IWF = Qt / C

Where:

Qt = Total weighted per-cycle water consumption for all wash cycles

C = Capacity

As discussed in the Engineering Chapter, DOE analyzed specific energy efficiency levels 

for top- and front-loading standard-capacity and compact residential clothes washers. Table 7.2.1

and 7.2.2 show the efficiency levels for standard-capacity residential clothes washers and their 

corresponding per-cycle energy and water use. Since the capacity varies with efficiency level 

there is a column including that volume variable (“Vol. ft3”). Both MEF and IMEF are also 

listed. The IMEF can be used to calculate total kWh/cycle, which can be broken down further 

into machine, dryer, and water heating energy. For example, in the table for top-loading washers 

the volume of 3.09 cubic feet divided by an IMEF of 0.84 results in a total kWh/cycle of 3.67

kWh, which also equals the sum of machine, dryer and water heating energy per cycle. Tables 

7.2.3 and 7.2.4 show the efficiency levels and the corresponding per cycle energy and water use 

for the two compact product classes.

Per-cycle energy use is disaggregated into energy used for heating the water, operating 

the machine, and drying the clothes. DOE determined the per-cycle clothes drying energy use by 

using RMC values contained in the cost/efficiency data from the engineering analysis. DOE 

obtained the per-cycle machine energy use from the cost/efficiency data set. After obtaining the 

per-cycle energy use for drying the clothes and operating the machine, DOE determined the percycle water-heating energy use. First DOE determined the total per-cycle energy use (the washer 

container volume divided by the IMEF) and then subtracted from it the per-cycle clothes-drying, 

standby, and machine energy use. The water-heating energy use assumes the use of an electric 

water heater. DOE determined the per-cycle hot water use by dividing the per-cycle waterheating energy use by an assumed temperature rise of 75 oF (21.1 oC) and a specific heat of 

0.0024 kWh/gal-oF (4.186 joule/gram-oC). DOE determined the total water use by multiplying 

the IWF by the washer container volume.
7-4

Some of the variables in the following four tables were calculated using average values. 

These average values are not used in the LCC analysis described in Chapter 8. The IMEF 

includes off-mode energy use and requires using an average value for washer usage (295 

cycles/year). An average dryer usage factor of 0.91 is used to calculate dryer energy use and this 

also impacts the calculation of water heater energy use; therefore, average values for these two 

quantities are shown in the two tables. When carrying out the LCC analysis, washer usage is 

selected from households in RECS. This methodology is described in Chapter 8.

Table 7.2.1 Top-loading Standard-Capacity Residential Clothes Washers: Per-Cycle 

Energy and Water Use by Efficiency Level

Level Vol

(ft3)

Watts MEF*IMEF

* IWF

(gal/cu ft)

RMC 

(%)

Energy Use (kWh/cycle)

Machine Dryer Water 

Heat+

Hot 

Water

gal/cycle

Baseline 3.09 0.00 1.26 0.84 9.92 51.9% 0.279 2.16 1.24 6.90

1 3.38 0.00 1.40 0.98 9.92 53.6% 0.281 2.43 0.74 4.13

2 3.38 0.00 1.72 1.29 8.44 48.8% 0.228 1.69 0.69 3.85

3 3.76 2.30 1.80 1.34 7.95 37.9% 0.082 1.41 1.26 7.02

4 3.76 1.70 1.80 1.34 7.95 37.9% 0.082 1.41 1.26 7.02

5 3.76 0.08 1.80 1.37 7.95 37.9% 0.082 1.41 0125 4.92

6 3.86 0.08 2.00 1.57 6.47 36.6% 0.082 1.38 0.99 5.50

7 3.96 0.08 2.26 1.83 4.96 36.6% 0.077 1.41 0.67 3.74

8 4.34 0.08 2.47 2.04 4.10 34.8% 0.082 1.39 0.66 3.67

* cubic feet/kWh/cycle + based on use of electric water heater
7-5

Table 7.2.2 Front-loading Standard-Capacity Residential Clothes Washers: Per-Cycle 

Energy and Water Use by Efficiency Level

Level Vol

(ft3)

Watts MEF*IMEF* IWF

(gal/cu ft)

RMC 

(%)

Energy Use (kWh/cycle)

Machine Dryer Water 

Heat§

Hot 

Water

gal/cycle

Baseline 3.00 2.30 1.72 1.37 8.31 41.4% 0.113 1.31 0.69 3.86

1 3.00 1.70 1.72 1.39 8.31 41.4% 0.113 1.31 0.69 3.82

2 3.00 0.08 1.72 1.41 8.31 41.4% 0.113 1.31 0.70 3.88

3 3.00 0.08 1.80 1.49 7.80 41.4% 0.113 1.31 0.60 3.31

4 3.30 0.08 2.00 1.66 6.26 41.6% 0.163 1.42 0.40 2.22

5 3.41 0.08 2.20 1.84 4.73 38.6% 0.154 1.34 0.36 1.99

6 3.60 0.08 2.40 2.02 4.42 38.7% 0.164 1.41 0.20 1.13

7 3.83 0.08 2.60 2.20 4.01 36.2% 0.167 1.37 0.21 1.14

8 3.90 0.08 2.89 2.46 3.39 35.9% 0.155 1.38 0.04 0.25

Table 7.2.3 Top-loading Compact Residential Clothes Washers: Per-Cycle Energy and 

Water Use by Efficiency Level

Level Vol

(ft3)

Watts MEF*IMEF* IWF

(gal/cu ft)

RMC 

(%)

Energy Use (kWh/cycle)

Machine Dryer Water 

Heat§

Hot 

Water

gal/cycle

Baseline 1.50 0.0 0.77 0.59 14.4 58 0.30 1.35 0. 90 4.98

1 1.59 0.0 1. 62 0.86 14.4 58 0.10 1.35 0.40 2.24

2 1.59 2.3 1.81 1.15 12.0 45 0.10 0.87 0.34 1.90

Table 7.2.4 Front-loading Compact Residential Clothes Washers: Per-Cycle Energy and 

Water Use by Efficiency Level

Level Vol

(ft3)

Watts MEF*IMEF* IWF

(gal/cu ft)

RMC 

(%)

Energy Use (kWh/cycle)

Machine Dryer Water 

Heat§

Hot 

Water

gal/cycle

Baseline 1.5 2.30 1.60 1.03 8.8 45 0.10 1.02 0.27 1.49

1 1.5 0.08 1.72 1.13 8.3 45 0.10 1.02 0.20 1.13
7-6

7.3 AVERAGE ANNUAL ENERGY AND WATER CONSUMPTION BY 

EFFICIENCY LEVEL

To determine the average annual energy and water consumption for a clothes washer, 

DOE multiplies the per-cycle energy and water consumption by the number of cycles per year. 

Because the predominant application of residential clothes washers is single-family housing 

units, including condominiums and mobile units, DOE considered only those applications in 

determining the number of clothes washer cycles per year. Other applications may include 

lodging establishments (e.g., some hotels and motels), but those are a minor part of the market 

compared to single-family housing units. DOE therefore believes it is not necessary for the 

analysis to accurately characterize residential clothes washer usage for applications other than 

single-family and multi-family housing units. In the LCC analysis, rather than using national 

averages, DOE determines clothes washer use by using a distinct value from RECS for each 

household.

DOE uses the following equation to calculate the annual energy consumption in each 

RECS household that is attributable to residential clothes washers. 

CWANNUAL = CWCYCLE × N

Where:

CWANNUAL = total annual energy consumption by clothes washers,

CWCYCLE = total per-cycle energy consumption by clothes washers (C/IMEF), and

N = individual household annual clothes washer use (loads per year).

DOE used the following equation to calculate the annual water consumption of 

residential clothes washers. 

CWANNUAL WATER = CWCYCLE WATER × N

Where:

CWANNUAL WATER = total annual water consumption by residential clothes washers, and

CWCYCLE WATER = total per-cycle water consumption by residential clothes washers.

The average annual energy and water consumption shown in Tables 7.3.1 through 7.3.4 

reflect an annual usage of 295 cycles per year. This is the average usage obtained from RECS 

2005. The total annual energy consumption reflects the use of an electric dryer and electric water 

heater. Total annual energy use equals Volume divided by IMEF multiplied by 295. This includes 

the non-active mode energy use. To convert electric water heating energy to gas or oil water 

heating energy use first convert kWh to Btu then divide by 0.75 to account for the efficiency of 

the water heater.
7-7

Table 7.3.1 Top-loading Standard-Capacity Residential Clothes Washers: Annual 

Energy and Water Use by Efficiency Level

Level IMEF*

IWF

(gal/cu

ft)

Annual Energy Use Annual 

Water Use

Total Machine Dryer Water 

Heat

(kWh) (kWh) (kWh) (kWh) (1000 gal.)

Baseline 0.84 9.92 1085 82 637 366 9.04

1 0.98 9.92 1019 83 717 219 9.89

2 1.29 8.44 770 67 499 204 8.41

3 1.34 7.95 831 24 416 372 8.82

4 1.34 7.95 826 24 416 367 8.82

5 1.37 7.95 808 24 416 368 8.82

6 1.57 6.47 725 24 407 294 7.36

7 1.83 4.96 639 23 416 200 5.79

8 2.04 4.10 629 24 410 195 5.25

Table 7.3.2 Front-loading Standard-Capacity Residential Clothes Washers: Annual 

Energy and Water Use by Efficiency Level

Level IMEF*

IWF

(gal/cu 

ft)

Annual Energy Use Annual 

Water Use

Total Machine Dryer Water 

Heat

(kWh) (kWh) (kWh) (kWh) (1000 gal.)

Baseline 1.37 8.31 644 33 386 205 7.36

1 1.39 8.31 637 33 386 203 7.36

2 1.41 8.31 626 33 386 207 7.36

3 1.49 7.80 596 33 386 177 6.90

4 1.66 6.26 585 48 419 118 6.10

5 1.84 4.73 546 45 395 106 4.76

6 2.02 4.42 525 48 416 61 4.69

7 2.20 4.01 513 49 404 60 4.53

8 2.46 3.39 467 46 407 14 3.91
7-8

Table 7.3.4 Top-loading Compact Residential Clothes Washers: Annual Energy and 

Water Use by Efficiency Level

Level IMEF*

IWF

(gal/cu 

ft)

Annual Energy Use Annual 

Water Use

Total Machine Dryer Water 

Heat

(kWh) (kWh) (kWh) (kWh) (1000 gal.)

Baseline 0.59 14.4 750 90 398 262 6.37

1 0.86 14.4 545 30 398 117 6.76

2 1.15 12.0 408 30 257 102 5.63

Table 7.3.3 Front-loading Compact Residential Clothes Washers: Annual Energy and 

Water Use by Efficiency Level

Level IMEF*

IWF

(gal/cu 

ft)

Annual Energy Use Annual 

Water Use

Total Machine Dryer Water 

Heat

(kWh) (kWh) (kWh) (kWh) (1000 gal.)

Baseline 1.03 8.8 430 30 301 80 3.89

1 1.13 8.3 392 30 301 61 3.63

7.4 VARIABILITY IN ANNUAL ENERGY AND WATER CONSUMPTION: 

WASHER CAPACITY AND USAGE TRENDS

Clothes washer usage measured in cycles per year varies from one household to another 

and therefore, so do energy and water use. The magnitude of the annual usage has been 

decreasing while the average capacity of washers has been increasing. Figure 7.4.1 shows washer 

capacity using AHAM data plotted with usage data. Capacity has increased by about 14% from 

1993 to 2005 while usage has decreased by about 17%4(RECS data) over the same time period. 

Assuming that any given household washes a fixed volume of clothes each year, this decrease in 

usage indicates that on average, larger amounts of clothes are being washed in each load.

The test procedure provides measurement methods for washers with and without load 

sensors. For washers with load sensors the test procedure gives the greatest weighting to a 

measurement with average loads (which means averaging maximum and minimum water fill 

results). This approach might result in calculated water and energy use that is unrealistically low 

if larger capacity washers tend to be filled with near maximum loads rather than average loads.
7-9

Figure 7.4.1 also shows washer usage decreasing over time. DOE has plotted results from 

analysis of RECS data and also market survey data. Both data sets show declining usage. The 

most recent average usage values from RECS 2005 and the market survey data show 295 and 

309 cycles per year, respectively. Each study has an advantage and a disadvantage in how they 

were conducted. The market survey study has actual point values for the weekly washes whereas 

the RECS study uses intervals. On the other hand, the market survey study household size 

distribution does not match the Census values for household size as well as the RECS study. 

Household size affects washer usage. The market survey data set has fewer single-person 

households and more multiple-person households. That can lead to a higher average usage value 

as is the case for market survey data relative to RECS 2005. The RECS 2005 household size 

distribution is close to that for the latest Census Bureau sampling and the American Housing 

Survey (AHS). 

Figure 7.4.1 Trends in Washer Usage and Capacity

DOE used RECS 2005 to determine the clothes washer usage in cycles per year for each 

household sampled in the LCC analysis. Figures 7.4.2 and 7.4.3 show the probability distribution 

of annual wash cycles for each product class. The average weighted usage is 295 cycles per year 

for top-loading clothes washers and 320 cycles per year for front-loading washers.

Annual Wash Cycles / Average 

Wash Tub Capacity

305

295

406

380

308

359

326

280

300

320

340

360

380

400

420

1981 1985 1989 1993 1997 2001 2005

Clothes Washer Cycles per Year

2.4

2.6

2.8

3

3.2

3.4

Tub Capacity (cu. ft)

RECS Market Survey Data Capacity
7-10

Figure 7.4.2 Annual Usage Distribution for Top-Loading Clothes Washers

Figure 7.4.3 Annual Usage Distribution for Front-Loading Clothes 

Washers
7-11

DOE also used RECS 2005 to determine the probability distribution of the dryer usage 

factors (DUF) for each household sampled. Figures 7.4.4 and 7.4.5 show the probability 

distribution of DUFs for both product classes. The vast majority of households use their dryers 

after every wash load.

Figure 7.4.4 Dryer usage for Households with Top-loading Clothes Washers
7-12

Figure 7.4.5 Dryer usage for Households with Front-loading Clothes 

Washers

DOE used the RECS household samples with their associated annual energy usage and 

DUF to conduct the LCC and PBP analyses. See chapter 8 for more details on the LCC and PBP 

analysis.
7-13

REFERENCES

 

1 U.S. Department of Energy–Office of Energy Efficiency and Renewable Energy. Energy 

Conservation Programs for Consumer Products: Final Rule; technical amendment. Federal

Register. October 18, 2005. 70 FR 60407. 

2 Biermayer, P.J. Preliminary Engineering Analysis for Clothes Washers. 1996. Lawrence 

Berkeley National Laboratory: Berkeley, CA. Report No. LBNL-47889, Appendix D. 

October.

3 U.S. Office of the Federal Register. Title 10, Code of Federal Regulations, Part 430–Energy 

Conservation Program for Certain Commercial and Industrial Product, Subpart B, Appendix 

JI—Residential Clothes Washers. 2010. Washington, D.C.

4

Energy Information Administration. Residential Energy Consumption Survey 2005. 

http://www.eia.doe.gov/emeu/recs/contents.html