Water Heater Energy and Cost Calculator
Work out the energy and cost to heat a tank of water. Enter the gallons, the cold inlet and hot outlet temperatures, your rate and the heater efficiency.
How to calculate water heating cost
- Enter the gallons of water you need to heat.
- Enter the cold inlet temperature and the target hot outlet temperature.
- Enter your electricity rate per kWh.
- Set the heater efficiency, then read the energy in kWh and the cost.
Examples
40 gallons from 50F to 120F
40 gal, 50F to 120F, $0.15/kWh, efficiency 1.0
70F rise, 23,352 BTU, about 6.84 kWh, roughly $1.03
Frequently asked questions
How much energy does it take to heat water?
It takes 1 BTU to raise 1 pound of water by 1 degree F. A gallon weighs 8.34 pounds, so 40 gallons up 70 degrees needs 23,352 BTU.
How do BTU convert to kWh?
Divide BTU by 3,412.142. So 23,352 BTU is about 6.84 kWh, which you then multiply by your electricity rate.
What inlet temperature should I use?
Cold supply water is often 45 to 60 degrees F depending on the season and region. A common target outlet is 120 degrees F.
How does efficiency change the result?
Energy is divided by the efficiency, so a lower figure means more energy and a higher cost. Electric resistance heaters are near 1.0.
Does this include standby or tank losses?
No. It covers the energy to raise the water temperature once. Real tanks also lose some heat while sitting idle.
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