FreeHVACCalculators

Start here

Loading calculators…

Menu

Water Heater Operating Cost Calculator (UEF)

The Uniform Energy Factor on a water heater’s label tells you how much energy it needs per unit of hot water. Combine it with your use and prices to get the yearly cost.

Method reviewed October 26, 2026. Version 1.0.0. How it works

Your inputs

Unit system

Printed on the EnergyGuide label and spec sheet. The default is only an example — enter your heater’s UEF.

The four DOE test usage patterns. The UEF on the label was measured at one of them (shown as the first-hour rating bin).

The DOE test heats 58 °F water to 125 °F (67 °F rise). Cold groundwater or a higher set point raises it.

US residential average: about $1.44/therm (EIA, Feb 2026).

Result

Yearly energy cost
$246
Average per month
$20.46

About $246 a year (171 therms) to heat 55 gallons a day with a UEF of 0.65.

Yearly energy use (therms)
171therms
Yearly energy use
17.05MMBtu
Hot water per day
55gal
Show the working
  1. Heat into the water per day = gallons × 8.24 lb/gal × 1.00 BTU/lb·°F × rise
    55 × 8.24 × 67 = 30,364 BTU
  2. Energy used per day = heat ÷ UEF
    30,364 ÷ 0.65 = 46,714 BTU
  3. Per year (× 365) in therms
    17,050,778 BTU ÷ 100,000 = 171 therms
  4. Yearly cost
    170.5 × $1.44 = $245.53

The method

The DOE test procedure heats water from 58 °F to 125 °F — a 67 °F rise — and uses one of four daily usage patterns: 10, 38, 55 or 84 gallons. The energy to heat the water each day is gallons × 8.24 lb per gallon × 1.00 BTU per pound per °F × the rise. Divide by the UEF for the energy the heater uses, multiply by 365, and convert:

  • Natural gas: ÷ 100,000 BTU per therm
  • Propane: ÷ 91,452 BTU per gallon
  • Electricity: ÷ 3,412 BTU per kWh

Comparing types

A higher UEF means less energy for the same hot water. Fuel-fired and electric-resistance heaters have UEFs below 1; heat pump water heaters move heat from the air rather than making it, so their UEFs are above 1. Compare costs with your own prices — the cheapest option depends on the price of each fuel where you live.

Heat pump water heaters cool the space they are in. In a heated basement or utility room, some of that heat comes back from your heating system in winter.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Water heater
Natural gas (tank or tankless)
Uniform Energy Factor (UEF)
0.65
Daily hot water use
Medium (55 gal/day)
Temperature rise (outlet − inlet)
67 °F
Natural gas price
1.44 $/therm

Result

Yearly energy cost
$246
Average per month
$20.46
Yearly energy use (therms)
171 therms
Yearly energy use
17.05 MMBtu
Hot water per day
55 gal

About $246 a year (171 therms) to heat 55 gallons a day with a UEF of 0.65.

Assumptions

  • Energy per year = 365 × gallons per day × 8.24 lb/gal × 1.00 BTU/lb·°F × temperature rise ÷ UEF, the form of the DOE test procedure’s annual energy equation.
  • Energy contents: 100,000 BTU per therm, 91,452 BTU per gallon of propane, 3,412 BTU per kWh (EIA).

Limitations

  • UEF was measured at one usage pattern and a 67 °F rise; at very different use or inlet temperature real efficiency shifts.
  • Heat pump water heater efficiency falls in cold rooms and when backup resistance elements run.
  • Excludes fixed utility charges.

Frequently asked questions

What is UEF?

The Uniform Energy Factor, the DOE’s measure of a water heater’s overall efficiency under its standard test procedure. It is printed on the EnergyGuide label and in product literature.

How much hot water does a household use?

The DOE test patterns range from 10 to 84 gallons a day; the medium pattern is 55 gallons. Your use depends on household size and habits — choose the closest pattern or enter your own.

Does the temperature setting matter?

Yes. A higher set point or colder incoming water increases the temperature rise and the energy used. Enter your own rise to see the effect.

Sources

  1. 10 CFR Part 430, Subpart B, Appendix E — uniform test method for consumer water heaters — U.S. Department of Energy, via eCFR (official API). Uniform Energy Factor (UEF) is the measure of water heater overall efficiency; inlet water 58 °F and delivery 125 °F; daily draws of 10, 38, 55 and 84 gallons for the very-small, low, medium and high usage patterns; annual energy uses 365 days, water density 8.24 lb/gal, specific heat 1.00 Btu/lb·°F and a 67 °F nominal temperature rise.
  2. Energy explained — British thermal units (Btu) — U.S. Energy Information Administration. 100,000 Btu per therm; 1,036 Btu/ft³ natural gas; 91,452 Btu/gal propane; 138,500 Btu/gal heating oil; 3,412 Btu/kWh.
  3. Electric Power Monthly, Table 5.6.A — average price to ultimate customers — U.S. Energy Information Administration. U.S. residential electricity price, 18.31 ¢/kWh in July 2026.
  4. U.S. Price of Natural Gas Delivered to Residential Consumers — U.S. Energy Information Administration. Monthly U.S. residential natural gas prices ($/Mcf).
  5. Heating Oil and Propane Update — U.S. Energy Information Administration. Weekly U.S. residential heating oil and propane prices during the heating season.

Spotted an error? Report a problem with this calculator — see our corrections policy.