Water Heater Cost Calculator
Estimate what it costs to heat your hot water each day, month and year from your usage, incoming water temperature and energy price.
How it works
Heat = gallons × 8.34 × (set − inlet) BTU · Electric kWh = heat ÷ 3412 ÷ 0.95 · Gas therms = heat ÷ 100,000 ÷ 0.60 · Cost = energy × price
A water heater spends energy raising incoming water from its cold inlet temperature up to the tank set point, so both how much you use and how cold your supply is drive the bill. One BTU heats one pound of water one degree, and a gallon weighs 8.34 pounds, which gives the raw heat demand. Dividing by the fuel’s energy content and heater efficiency turns that heat into kWh or therms you actually pay for — electric resistance is nearly 95% efficient, while a standard gas tank wastes more up the flue.
Worked example
Using 64 gallons a day, heated from 55°F to 120°F (a 65°F rise), needs 64 × 8.34 × 65 ≈ 34,700 BTU. On electric resistance that is 34,700 ÷ 3412 ÷ 0.95 ≈ 10.7 kWh, and at $0.17/kWh about $1.82 a day — roughly $55 a month.
Frequently asked questions
Does lowering the set temperature save much?
Yes. Energy use is proportional to the temperature rise, so dropping from 140°F to 120°F on a 55°F inlet cuts the rise from 85°F to 65°F — about a 24% reduction in heating energy. 120°F is the common recommended balance of savings and scald safety.
Why is gas often cheaper than electric here?
Even though a gas tank is less efficient, natural gas usually costs far less per unit of heat than electricity. This estimate lets you compare directly by plugging in your own per-kWh and per-therm prices.
Does this include standby (tank) losses?
No — it estimates the energy to heat the water you draw. A storage tank also loses heat while idle, which a heat-pump or tankless unit reduces. Treat this as the usage-driven core of the bill.
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This calculator is for educational purposes. Double-check important results before acting on them.