How it’s calculated
- Heat per day (BTU) = gallons × 8.34 × (setpoint − inlet)
- Yearly input = daily heat × 365 ÷ UEF
- kWh = BTU ÷ 3,412; therms = BTU ÷ 100,000
Worked example
60 gal/day, 55 °F inlet, 120 °F setpoint, electric resistance UEF 0.92, $0.17/kWh.
Inputs
- Hot water used per day
- 60 gal
- Incoming water temperature
- 55 °F
- Tank setpoint
- 120 °F
- Fuel
- Electric (resistance or heat pump)
- Uniform Energy Factor (UEF)
- 0.92
- Electricity rate
- 0.17 $/kWh
- Natural gas rate
- 1.4 $/therm
Results
- Yearly cost
- $642.92
- Yearly energy (electric)
- 3,782 kWh
- Monthly cost
- $53.58
Assumptions and limits
- UEF already includes standby losses at rated conditions; real use patterns differ.
- Inlet temperature is a yearly average.
Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.
Questions
How much does it cost to run an electric water heater?
A typical family using 60 gallons a day pays around $640 a year at $0.17/kWh with a resistance heater. A heat pump water heater cuts that by roughly two-thirds.
Does lowering the setpoint save energy?
Yes. Energy is proportional to the temperature rise. Many households use 120 °F.