Water Heater Running Cost Calculator
Water heating is typically the second-largest line on a home energy bill. This compares the three main types honestly, including the standby loss most calculators leave out.
Rates and assumptions reviewed · see every source
How this is calculated
Heating water is simple physics. One US gallon weighs 8.34 lb, and raising 1 lb of water by 1°F takes 1 BTU. So:
BTU/day = gallons × 8.34 × temperature rise
kWh/day = BTU ÷ 3,412 ÷ efficiency, plus standby loss
Efficiencies used: electric resistance 95%, heat pump 300% (it moves heat rather than making it), gas storage tank 60% once flue and standby losses are counted.
Standby loss: the bill you pay for nothing
Your tank holds 40–80 gallons at 120°F all day, every day. Heat leaks out through the insulation continuously, and the heater keeps topping it back up.
On a modern well-insulated tank that is roughly 0.6 kWh a day. On a 15-year-old tank in an unheated garage it can exceed 2 kWh. At 18.3¢/kWh that older tank burns $134 a year keeping water hot that nobody uses — including every day you are on holiday.
Cheapest fix available: an insulating blanket costs $20–40 and cuts standby loss 25–45% on an older tank. It typically pays for itself within a year. Do not fit one to a newer tank that is already well insulated, and never cover the top of a gas unit or block its air intake.
The three options compared
| Type | Annual running cost | Installed cost | Life |
|---|---|---|---|
| Electric resistance tank | $550–750 | $900–1,800 | 10–12 yrs |
| Heat pump water heater | $180–260 | $2,200–3,500 | 13–15 yrs |
| Gas storage tank | $280–420 | $1,100–2,200 | 8–12 yrs |
| Gas tankless | $230–350 | $2,500–4,500 | 18–20 yrs |
3-person household, 65°F rise, $0.1834/kWh, $1.55/therm.
The honest verdict
If you have electric water heating, a heat pump model is close to a no-brainer. Roughly a third of the running cost, three-to-five year payback, and federal tax credits often cover a chunk of the difference. The only real barriers are space and where the cool exhaust air goes.
If you have gas, stay with gas unless you are already electrifying the house. Gas water heating is cheap to run at current rates, and switching to a heat pump saves little while costing a lot.
Tankless is a comfort purchase, not a financial one. Endless hot water and a reclaimed closet are genuine benefits. The energy saving alone rarely repays the installation.
Free changes worth making today
- Set the tank to 120°F. Saves 6–10% versus the 140°F many units ship at, and reduces scald risk.
- Fix dripping hot taps. One drip per second wastes roughly 1,600 gallons of heated water a year.
- Fit low-flow showerheads. Cuts hot water use 25–40% with little noticeable difference.
- Insulate the first six feet of hot pipe. A few dollars, small but permanent saving.
Common questions
What is standby loss and why does it matter?
A storage tank keeps 40–80 gallons hot around the clock, and heat continuously leaks through the insulation. Reheating that lost warmth costs money even during a week away from home. On an older tank it can be 1–2 kWh a day — $60–130 a year for hot water nobody used. Tankless heaters have almost none, which is a real part of their appeal.
Is a heat pump water heater worth the extra cost?
Usually yes, if you have electric water heating now. A heat pump model uses roughly a third of the electricity of a resistance tank, saving $300–500 a year for perhaps $1,200–2,000 extra installed — a three-to-five year payback on a unit lasting 13–15 years. Two caveats: they need about 700 cubic feet of surrounding air space, and they cool and dehumidify that space, which is a bonus in a garage and a nuisance in a finished basement.
Does tankless save money?
It eliminates standby loss, which typically saves $50–120 a year. But installation runs $2,000–4,500 versus $900–1,800 for a tank, and gas models often need a larger gas line and new venting. The payback is frequently longer than the unit's life. Buy tankless for endless hot water and the space saving, not as an investment.
What temperature should I set it to?
120°F is the usual recommendation. It is hot enough to suppress Legionella growth in most systems, reduces scald risk, and lowers both standby loss and heating energy compared with the 140°F many units ship at. Dropping from 140°F to 120°F typically saves 6–10% of water heating cost. If anyone in the household is immunocompromised, ask a plumber before lowering it.