How to use this calculator
Most plug-in resistance heaters turn nearly all electricity at the outlet into room heat. Cost comes mainly from wattage and how long the thermostat keeps the element energized.
- Check the selected heat setting in watts.
- Estimate active heating time rather than total time switched on.
- Add multiple heaters with the quantity field.
FORMULA
The math behind the estimate
heater watts × active hours × quantity ÷ 1,000 × rate = cost.
Worked example
One 1,500 W heater active six hours a day at $0.18/kWh costs about $49 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
- Thermostat cycling is represented through active hours.
- Only plug-load energy is included.
- Manufacturer clearances and safety rules come first.
Climate, equipment condition, installation, controls, and household behavior can materially change results. Verify consequential installation and purchasing decisions with qualified providers.
Practical savings context
Heat the smallest practical zone, close drafts, and avoid running an empty room.
SOURCE
Data and methodology
U.S. Department of Energy — Small Space Heaters
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
Space heater FAQ
How accurate is this space 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