Heat Pump Water Heater Savings Calculator
A heat pump water heater moves ambient heat into the tank rather than generating heat directly, so it uses much less electricity than a standard resistance tank for the same hot water. This calculator compares the two on annual running cost. Annual cost equals the useful delivered hot water energy divided by the uniform energy factor (UEF) of the heater, times your electricity rate. Dividing by UEF converts delivered energy into purchased energy, so a higher UEF means lower cost. The savings is simply the difference between the two annual costs. Both UEF values and the delivered energy are user-editable inputs, so the comparison reflects your own equipment and hot water use.
Running cost formula
Heat pump kWh = delivered energy / heat pump UEF
Resistance kWh = delivered energy / resistance UEF
Annual cost = purchased kWh * electricity rate
Annual savings = resistance cost - heat pump cost
Dividing delivered energy by UEF gives the purchased electricity. The same delivered energy is used for both heaters so the comparison is fair.
Water heater efficiency context
- UEF is the federal uniform energy factor, the ratio of delivered to purchased energy.
- Heat pump water heaters commonly reach a UEF around 3 or more; resistance tanks are below 1.
- A higher UEF means less purchased electricity for the same hot water.
- Heat pump units lose efficiency in cold installation spaces; lower the UEF to reflect this.
- ENERGY STAR lists qualified high-efficiency heat pump water heaters.
Heat pump water heater: frequently asked questions
How does a heat pump water heater save money?
A heat pump water heater moves ambient heat into the tank instead of generating heat directly, so it uses far less electricity for the same hot water. Its uniform energy factor (UEF) is typically around 3 or more, against roughly 0.9 for a standard electric resistance tank, so it draws a fraction of the power.
What is the uniform energy factor (UEF)?
UEF is the standardised efficiency rating for water heaters, the ratio of useful hot water energy delivered to the energy the heater consumes, measured under a federal test procedure. A higher UEF means less purchased energy for the same hot water. Both UEF values here are user-editable inputs.
How is annual running cost calculated?
Annual cost equals the delivered hot water energy divided by the UEF, times the electricity rate. Dividing by UEF converts useful delivered energy into purchased energy, and multiplying by the rate converts kilowatt-hours into dollars. The savings is the difference between the two heaters' annual costs.
What delivered energy should I enter?
Delivered energy is the useful hot water energy your household needs per year in kilowatt-hours, which depends on hot water use and incoming water temperature. Enter your own estimate; the same delivered energy is used for both heaters so the comparison is fair.
Does ambient temperature affect heat pump water heaters?
Yes. Heat pump water heaters draw heat from the surrounding air, so they perform best in warm spaces and lose efficiency in cold ones, where backup resistance elements may engage. Lower the heat pump UEF input to reflect a cold installation location.
Official sources
- U.S. Department of Energy: Heat Pump Water Heaters.
- ENERGY STAR: Heat Pump Water Heaters.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.