Water Heater Energy and Cost Calculator

It takes 1 BTU to raise 1 pound of water by 1 degree Fahrenheit. A US gallon weighs 8.34 pounds, so heating 40 gallons by 70 degrees needs 40 times 8.34 times 70, which is 23,352 BTU.

Divide the BTU by 3,412.142, the number of BTU in one kilowatt-hour. So 23,352 BTU is about 6.84 kWh, which you then multiply by your electricity rate to get the cost.

Cold supply water is often 45 to 60 degrees Fahrenheit depending on the season and your region, running colder in winter. If you are unsure, 50 degrees is a reasonable middle estimate for a rough figure.

A common household setting is 120 degrees Fahrenheit, which balances comfort, scald safety and energy use. Some raise it to 140 to fight bacteria, but that uses more energy and needs care to avoid scalding.

The energy is divided by the efficiency, so a lower figure means more energy in and a higher cost. Electric resistance heaters are close to 1.0, while other systems lose some heat and sit lower.

Yes. Switch the unit toggle to Celsius and enter both temperatures in Celsius. The tool converts them internally and shows the temperature rise back in the unit you selected.

No. It covers the energy to raise the water temperature one time. A real storage tank also loses heat while sitting idle and reheats to stay warm, so your monthly bill runs higher than a single heating cycle suggests.

The math is for electric heating priced per kilowatt-hour. You can approximate a gas heater by lowering the efficiency toward its energy factor, but for an accurate gas cost you would price therms of natural gas instead.

Your utility bill lists a price per kilowatt-hour, often between 10 and 30 cents in the US. Use your all-in rate including delivery charges for the most realistic cost.