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Sources for the Laundry Calculator

 last updated April 2011

This page shows where I got my figures for my deluxe laundry calculator, and is probably of interest to nobody. This page exists only so that I can properly "show my work".  If you're looking to calculate your own laundry costs, or want tips on saving money on laundry, then the actual laundry page will be much more useful.

Shame on laundry machine manufacturers

No U.S. manufacturer bothers to list how much water or energy their models use on a per-load basis.  Shame on them.  Laundry calculations would be a lot easier if the manufacturers deigned to provide this very basic information about the products they make.

General figures & notes

Sample price of electricity ($0.15/kWh). My cost of electricity page.
Average price of gas ($1.23/therm).
Dept. of Energy, avg. for 2009. 1 MCF=10.25 therms, so divide $/MCF by 10.25 to get $/therm
Average price of water, excluding sewer/wastewater ($2.72/thousand gallons).
EPA (PDF), 2000, p. 29  You might also be interested in the cost per state, 2003.
Average price of wastewater ($2.72/thousand gallons). USA Today (2007) says that wasterwater is pretty much equal to water costs
Total avg. price of water+wastewater ($5.44/thousand gallons). Sum of above two figures.

Hot wash temperature: (106F/41C). From the manual for the Asko WL6511 (p. 18).  Note that old machines don't regulate the temperature, and just use the incoming hot water temp.  Most washer makers don't bother to disclose the water temperatures used, shame on them.
Warm wash or rinse temperature: (88F/31C). From the manual for the Asko WL6511 (p. 18).  An LG model I found uses 86F.  Older machines don't regulate the temp. and just mix hot+cold blindly to get warm.
Cold temperature: (-). Some machines heat cold water to a minimum level to make sure detergents dissolve properly.  The calculator assumes the cold water isn't heated.
Temperature of groundwater (57F).  Varies from 35-77F in the U.S.  Eyeballing a temperature map, adjusting for population centers, 57F seems like a good average.

Wh to heat a gallon of water by 1F (0.00263).
From my
water heaters page.
Therms to heat a gallon of water by 1 (0.00014). From my water heaters page.
Loads of laundry per year (392). EPA.

Top-Loader figures

kWh per load, machine only (0.256). Modesto Irrigation Dist. An EPA Excel Spreadsheet gives 0.21 and the Multi-Housing Laundry Assoc. gives 0.30 kWh. I'm taking the middle figure.
Cost of electricity per load (4). 15/kWh x 0.256 kwh = 3.84.

Gallons per load (40). California Energy Commission. MHLA gives 34 gallons.
Cost of water per load (22). $5.44/1000 x 40 = 21.76.

Portion of water in wash vs. rinse cycle (50/50). EnergyGuide.
Portion of water that's hot, on hot setting (100%). Educated guess.  Top-loaders generally don't heat the water, they rely on the water coming through the hot water line to already be heated. (Repair Clinic)
Portion of water that's hot, on warm setting (50%). Educated guess.
Gallons of hot water for Hot/Warm setting (30). 20 gallons hot for wash, 10 gallons hot for rinse
Gallons of hot water for Warm/Warm setting (20). 10 gallons hot for wash, 10 gallons hot for rinse
Gallons of hot water for Warm/Cold setting (10). 10 gallons hot for wash

Electricity Savings per year by switching from Hot/Cold to Cold/Cold ($152). 20 gallons hot x 49F rise x 0.00263 Wh/1F/gallon x $0.15/kWh x 392 loads per year

Therms to heat a gallon of water from 57 to 130F, i.e. 73F (0.01022). 73 x 0.00014 therms (from "General", above)

Front-Loader figures

Premium for front-loader purchase ($100).  According to in April 2010, comparing the cheapest front-loader to the cheapest top-loader.
Energy savings vs. top-loader (30-85%).
EPA , excluding small washers (less than 3 cu. ft.) to be fair.  That's 120-560 kWh/yr. vs. 800 kWh/yr.
Water savings vs. top-loader (40-75%).
EPA , excluding small washers (less than 3 cu. ft.) to be fair.  That's 10-24 gallons vs. 40 gallons.
Gallons per load (14.7). Oct. 2008 spreadsheet downloaded from the EPA's clothes washers page.
Gallons per wash cycle (12.2).
The average front-loader uses 14.7 gallons of water according to the EPA, above.  An old version of the user manual for the Asko WL5611 said it uses 14.3 gallons total and 2.4 gallons for the Rinse cycle, which would be 11.9 gallons for the Wash. The Wash is thus 83.2% of the total water. So I figure a typical front-loader uses 14.7 gallons x 83.2% = 12.2 gallons. From there I apply the kWh and therms to heat water as per the earlier sources.
Cost of water per load (8). 14.7 gallons x $5.44/1000

kWh per load, machine only (0.26). I've been completely unable to find this information, so I used the same figure as for a top-loader, which should be fairly similar, since the real energy savings from a front-loader is in using less water and thus using less energy to heat the water. Not a single manufacturer of Energy Star washers in the U.S. bothers to publish how much electricity its washers use per cycle. Shame on them. Anyone who's got a front-loading washer and a watt-hour meter, please wash a load in cold and let me know how much it used.
Cost ef electricity per load (4). 15/kWh * 0.26

Source of hot water. Front-loaders sold in the U.S. generally have both hot and cold water connections, so the home water heater is doing the water-heating.  European front-loaders generally have only a cold water connection, so the washer is heating the water, electrically.  The calculator assumes a U.S.-style washer. U.S. washers do generally control the temperature, for both front- and top-loaders, though not all do.  (e.g., in Maytag & Whirpool some models do and some don't; one Frigidaire model I found regulates the wash temp but not the rinse.)  I checked user manuals in 4/2010 for a plethora of U.S. manufacturers to confirm all the above.

Heat rise for Hot setting (49F). 57F (from "General", above) to 106F
Heat rise for Warm setting (31F). 57F (from "General", above) to 88F
Cost of extra electricity for Hot wash (25). 12.7 gallons x 49F x 0.00263 kWh/gallon/1F (from "General", above) x 15/kWh.
Cost of extra electricity for Warm wash (16).
12.7 gallons x 31F x 0.00263 kWh/gallon/1F x 15/kWh.
Cost of extra electricity for Warm rinse (3).
2.5 gallons x 31F x 0.00263 kWh/gallon x 15/kWh.

Cost of gas per Hot wash (11). 12.7 gallons x 49F rise x 0.00014 therms/gallon/1F x $1.23/therm.
Cost of gas per Warm wash (7).
12.7 gallons x 31F rise x 0.00014 therms/gallon/1F x $1.23/therm.
Cost of gas per Warm rinse (1). 2.5 gallons x 31F rise x 0.00014 therms/gallon/1F x $1.23/therm.

Reduction in drying time vs. top-loader (7%). Oak Ridge Natl. Laboratory, 1998

Dryer figures

Electric dryers.  Here are the various figures I found, with the sources in parentheses:

  1. 3.0 kWh per load (MID)
  2. 3.3 kWh per load (MLA; this is what I use in the calculators)
Note that you can't use the label on an electric dryer to figure the amount of energy used, because the heating element isn't on the whole time during the drying cycle.

Gas dryers, electric component.  Here are various figures for the amount of electricity required to spin the drum.

  1. 0.21 kWh per load (from my own measurement of a standard-size Kenmore gas dryer for a 45-minute cycle; this is what I use in my calculators)
  2. 0.30 kWh per load (Modesto Irrigation District, PDF)
  3. 0.50 kWh per load (MLA)
In my test, the load dropped from 325 watts at the start to 260 by the end of the cycle, because as the clothes got drier they got lighter and so it took less energy to spin the drum.

Gas dryers, gas.  I found various figures for therms per load for clothes dryers:

  1. 0.17 therms/load (MLA)
  2. 0.20 therms/load for 5.8 cf dryer (Metropolitan Utilities District, PDF)
  3. 0.22 therms/load (City of Ukiah; this is what I use in my calculators)
  4. 0.25 therms/load for 7.3 cf dryer (Metropolitan Utilities District, PDF)
  5. 0.28 therms/load (RG&E)
I also found various figures for the BTUs per hour for dryers:
  1. 18,500 BTUs per hour (JLC)
  2. 20,000 BTUs per hour  (Minnesota Energy, Metropolitan Utilities District for 5.8 cf dryer)
  3. 25,000 BTUs per hour (Metropolitan Utilities District for 7.3 cf dryer)
  4. 35,000 BTUs per hour (King County, Mark Heard Fuel, Engineering Toolbox)
  5. 52,000 to 70,000 BTUs per hour, for a comercial dryer (Planet Laundry)
1 therm = 100,000 BTUs, so 18,500 to 35,000 BTUs per hour is 0.185 to 0.35 therms per hour.  For a 45-minute load, that's 0.14 to 0.26 therms, which is right in line with the therms per load figures above.
Some readers complained that the figures above assume that the dryer is operating at full-blast all the time.  But my understanding is that gas dryers do operate at full-blast all the time, and if you choose a lower heat setting, then it simply takes longer for your clothes to dry, so you wind up using the same amount of energy either way.  Besides, my reading of some of the sources above is that they're truly reporting the energy use per hour, meaning that they're already accounting for any decreased output rate.

Dryer capacity.  On 3/31/11 I looked at every dryer on and most had drums between 5.7 to 8.0 cubic feet, though some were as large as 8.0 cf, and there were a few ultra-compact models in the 3.4 to 3.6 cf range.  Note that the dryer size doesn't affect the energy use per load very much, because a load of wet clothes is going to take X amount of heat to remove regardless of the dryer's drum size (assuming that the dryer is big enough to move sufficient air through the clothes).

Gas vs. Electric market share.  About 77% of U.S. dryers are electric, vs. 23% for gas. (EPA, 2001)

Links to related info


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