What does a water heater cost to run?
Pick your state and appliance. The efficiency figure is not something you have to look up — it is derived from the class and capacity, and you can override it with the number on your own label.
For tanks, sets both the usage bin and the coefficient the federal minimum uses. Ignored for tankless units.
The starting value of 64 gallons a day is our assumption, not a published figure. Federal guidance treats 41 gallons a day or less as low use and around 86 as high use. Enter your own.
Assumed 55 °F to start, not a published figure; change it to your own.
Assumed 120 °F to start, the setting we chose; change it to yours.
Leave at zero to use the legal minimum for this class. A real appliance may beat it — the yellow label has its rating.
Cost to run for a year
$670
Single-valued: the federal minimum efficiency for this class is one number, so the only honest spread here is the sensitivity to how much hot water the household really draws, shown separately below.
About $56 a month. Draw a quarter less hot water and it is $502; draw a quarter more and it is $837. The state you pick can move it further: the same inputs give $503 a year in Idaho and $2,118 in Hawaii. Excluded: the standing charge on your bill, which you pay whether or not you heat any water.
| Step | Value |
|---|---|
| Temperature rise | 65 °F |
| Heat delivered to the water each year | 12,647 thousand Btu |
| Efficiency, federal minimum for this class | 0.91 |
| Fuel actually burned | 4,073 kilowatthours |
| Delivered price in Texas | 16.44¢ per kilowatthour |
| On a common energy basis | $48 per million Btu |
How that efficiency figure was reached: 0.9254 − (0.0003 × 50 gal) = 0.91 This is the floor the law sets for the class, not a rating for any particular appliance, and it is labelled sourced accordingly.
A published range for this appliance type puts annual running cost at $530 to $600 (historical cost estimate, archived copy dated August 8, 2025). Our figure is $670. If those are far apart, the hot-water volume, the efficiency floor and the state price used here may all differ from theirs; theirs are not stated.
The whole calculation, in three lines
Heating water is one of the few household energy questions with genuinely simple physics. A gallon of water weighs 8.329 pounds[1], and raising one pound of water by one degree Fahrenheit takes one British thermal unit. So the heat your household actually needs is gallons drawn, times 8.329, times the temperature rise, times 365 days. Nothing about the appliance enters yet — that is the heat the water demands regardless of what supplies it.
The appliance enters once, as a divisor. Divide the heat delivered by the uniform energy factor and you get the fuel actually burned, including everything lost through the tank wall while nobody is drawing. Then convert to whatever you are billed in: 3,412 Btu to the kilowatthour[2], 100,000 Btu to the therm[2], 91,452 Btu to the gallon of propane[2]. Natural gas needs one extra step because it is priced per thousand cubic feet and burned per therm: at 1,037 Btu per cubic foot[3], a thousand cubic feet is 10.37 therms.
That is the entire model. There is no fudge factor and no seasonal adjustment, which is worth knowing because it tells you exactly where the answer can be wrong: it can be wrong about how much hot water you draw, and it can be wrong about how closely a laboratory efficiency rating matches your real duty cycle. It cannot be wrong about the arithmetic.
Where the efficiency number comes from, and why it is a floor
This calculator derives an efficiency rating rather than asking for one. Federal standards state a minimum uniform energy factor as a formula in rated storage volume, selected by product class and by the usage bin the first-hour rating lands in. The tool picks the bin by treating the tank’s rated volume as its first-hour rating, and a tankless unit as if it were rated at forty gallons. That is our assumption, not a federal rule. It puts a fifty-gallon tank in the low-usage bin, whose minimum is lower than the medium bin’s, so the running cost reported is higher than a medium-bin rating would give.
The important caveat, and it is repeated beside the answer rather than buried here: a minimum is a floor. It is what an appliance is forbidden to be worse than, not what any particular appliance is. A real appliance may beat it. That is why the tool takes your own label figure and uses it instead when you have one, and why the estimate without it should be read as the cautious end rather than the expected outcome.
Heat pumps get a specific and honest treatment. Above fifty-five gallons the electric storage minimum is greater than 1.0, which resistance heating cannot physically reach, so those rows describe heat pumps and are used exactly as published. At or below fifty-five gallons the minimum is the resistance floor and says nothing about a heat pump at all — so there the site applies the published statement that a heat pump is 2 to 3 times as efficient as resistance[4], uses the midpoint of that range (our choice), shows the multiplication on screen, and labels the result derived rather than sourced. It is our arithmetic, not somebody else’s measurement, and the page says which.
What running cost does not capture
The same federal guidance notes that a heat pump water heater tends to cool the space it is in and will not operate efficiently in a cold space. It also requires a space that stays between 40 and 90 degrees year round with at least 1,000 cubic feet of air around the unit[4]. This site has no figure for how a heat pump performs outside those conditions, so none of its running-cost numbers apply there.
Published running-cost ranges are worth having as a sanity check even though they hide their assumptions. One cost guide, in an archived copy dated August 8, 2025, puts an electric tank at $530–$600 a year and a heat pump at $160–$190[5]. The tool prints its own figure next to whichever of those applies. If they are far apart, the hot-water volume, the efficiency floor and the state price used here may all differ from theirs; theirs are not stated.
National fallbacks, used only where a state figure genuinely does not exist: 18.44 cents per kilowatthour (U.S. average for May 2026, which EIA marks preliminary)[6], $15.34 per thousand cubic feet of gas (2025 annual average)[7], and $2.674 a gallon for propane (week ending March 30, 2026, excluding taxes)[8].
Questions people actually ask
How much does it cost to run a water heater per month?
It depends on your fuel, your state, your appliance and how much hot water you use. The tool above computes it from the heat your household draws, the legal minimum efficiency for that appliance class, and the published residential price where you live. On the tool's starting inputs an electric tank costs $503 a year in Idaho and $2,118 in Hawaii.
Why is a heat pump water heater so much cheaper to run?
Because it moves heat rather than making it. The federal guidance is that a heat pump water heater is 2 to 3 times as efficient as electric resistance, which is not an efficiency improvement in the ordinary sense: a resistance element cannot exceed one unit of heat per unit of electricity, and federal guidance says a heat pump can be two to three times as efficient.
Where do these energy prices come from?
Electricity is the May 2026 residential price for your state from EIA's archived July 2026 Electric Power Monthly, which EIA marks preliminary. Natural gas is the 2025 annual residential price per thousand cubic feet from EIA's release of September 30, 2026, converted to therms at 1037 Btu per cubic foot. Propane is the U.S. residential price from EIA's weekly series, so every state shows the same figure. These are historical prices, not today's rates. In that release six states have no annual figure, and the tool says so rather than borrowing a neighbour's.
Is this what my bill will say?
No, and nothing that works this way can be. Efficiency ratings are measured against a standard laboratory draw pattern, not your household, and your bill also carries a standing charge you pay regardless. Treat this as a comparison instrument — good for ranking two appliances on identical assumptions — rather than as a forecast.
Sources for the numbers above
- U.S. Geological Survey, Water Science School — Archived source dated August 16, 2026: https://web.archive.org/web/20260816183627/https://www.usgs.gov/water-science-school/science/water-density (checked 2026-08-06; re-checked 2026-10-05). The sentence has since been removed from the live page.
- U.S. Energy Information Administration — https://www.eia.gov/energyexplained/units-and-calculators/british-thermal-units.php (retrieved 2026-08-06)
- U.S. Energy Information Administration — https://www.eia.gov/tools/faqs/faq.php?id=45&t=8 (retrieved 2026-08-06) [one figure drawn from this source is derived — the arithmetic is shown on the methodology page]
- U.S. Department of Energy, Energy Saver (archived) — Archived source dated June 30, 2026: https://web.archive.org/web/20260630092818/https://www.energy.gov/energysaver/heat-pump-water-heaters (checked 2026-08-06; re-checked 2026-10-01)
- HomeGuide — Historical cost estimate — archived source dated August 8, 2025: https://web.archive.org/web/20250808205107/https://homeguide.com/costs/water-heater-installation-cost (checked 2026-08-06; re-checked 2026-10-05). The live page refused an automated check on 2026-10-05, so whether it still prints these figures is not known.
- U.S. Energy Information Administration — Historical figures — EIA Electric Power Monthly, July 2026 issue (archived), Table 5.6.A, May 2026 data, marked preliminary by EIA: https://www.eia.gov/electricity/monthly/archive/july2026.pdf (checked 2026-08-06; re-checked 2026-10-05). The live table has since moved on to later months and no longer shows these May 2026 values.
- U.S. Energy Information Administration — https://www.eia.gov/dnav/ng/hist/n3010us3a.htm (retrieved 2026-10-05)
- U.S. Energy Information Administration — https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=W_EPLLPA_PRS_NUS_DPG&f=W (retrieved 2026-08-06). Historical U.S. residential propane price: $2.674 per gallon, excluding taxes, for the week ending March 30, 2026. Re-verified October 25, 2026 in EIA’s historical series (release dated October 21, 2026). The rolling weekly table has moved on; this is not the latest price or a local delivery quote.