How to use this calculator
Tank heaters do not draw full element power continuously. Heating time depends on hot-water use, incoming-water temperature, tank losses, and thermostat settings.
- Use active element wattage from the label.
- Estimate combined heating time across the day.
- Model low and high usage to see a range.
FORMULA
The math behind the estimate
element watts × active heating hours ÷ 1,000 × electricity rate = energy cost.
Worked example
A 4,500 W element active three hours a day at $0.18/kWh costs about $74 per average month.
Change the defaults to model your home. The result is an estimate, not a guaranteed bill or savings promise.
How to read the result
Use the estimate to compare scenarios and find the inputs worth measuring more carefully. Utility bills can include fixed charges, taxes, delivery fees, minimums, tiers, and demand charges that are not fully represented by a simple energy rate.
Assumptions and limitations
- Only one element is active at a time.
- Standby losses are represented through runtime.
- Heat-pump water heaters need a model-specific method.
Climate, equipment condition, installation, controls, and household behavior can materially change results. Verify consequential installation and purchasing decisions with qualified providers.
Practical savings context
Use safe temperature settings, repair leaks, insulate eligible pipes, and choose efficient fixtures.
SOURCE
Data and methodology
U.S. Department of Energy — Water Heating
Guidance accessed August 2026. Geographic scope: United States. Last reviewed: August 6, 2026.
WattMeasure uses the source to frame the method and assumptions; your editable inputs determine the displayed result.
QUESTIONS
Water heater FAQ
How accurate is this water heater estimate?
It is a planning estimate based on the values you enter. Actual power draw, cycling, utility charges, climate, and equipment condition can change the result.
Should I use the default electricity rate?
Your own marginal or all-in supply rate is better. Check a recent bill or your utility's published rate schedule.
Does this include taxes and utility fees?
Only when they are reflected in the rate you enter. Fixed monthly charges are not included because they usually do not change with one appliance's usage.
Last reviewed August 6, 2026 · Data update policy