The short answer
A 1,500 W heater costs 1.5 kWh × your rate for every hour it is actually heating. Four hours a day for a month at $0.20/kWh is $36. A thermostat reduces that by switching it off once the room is warm, so the nameplate figure is the ceiling.
The arithmetic
Electric resistance heaters turn nearly all of their electricity into heat, so watts in equals heat out. That makes the calculator's watts-and-hours mode accurate for a heater running flat out. What the label cannot tell you is how many minutes per hour the thermostat keeps it on, which depends on the room, the setpoint and how drafty the windows are.
Worked examples
| Scenario | kWh / day | kWh / period | Cost / period |
|---|---|---|---|
| 1,500 W × 4 h/day, flat out | 6 | 180 | $36.00 |
| 750 W setting × 4 h/day | 3 | 90 | $18.00 |
| 1,500 W, thermostat on half of 8 h/day | 6 | 180 | $36.00 |
Basis: Nameplate arithmetic. The first row is the common 1,500 W ceiling; the second shows the same heater on its 750 W setting; the third assumes a thermostat holding the heater on half the time, which is an assumption, not a measurement.
A low setting changes heat output, not efficiency
Every resistance heater is equally efficient at turning electricity into heat, whatever the brand or the price. The 750 W setting simply produces half the heat; if the room needs the full 1,500 W to hold temperature, it will run twice as long. What changes the bill is heating a smaller space for fewer hours, and losing less heat through the windows, which is where draft-sealing comes in.
Direct to the wall, and never through a meter
Plug electric space heaters directly into a wall outlet, keep them clear of anything combustible, and do not put a plug-in meter, smart plug, extension cord or power strip between the heater and the outlet. Cost a heater from its nameplate; do not measure it inline.
Sources and evidence
What we are relying on
- Energy cost for a steady load = watts ÷ 1,000 × hours per day × days × your rate in dollars per kWh.
- Arithmetic method, not a measurement. Appliances that cycle on and off need measured kWh or actual runtime, not nameplate watts × 24 hours.
- CPSC guidance says to plug electric space heaters directly into a wall outlet and keep them clear of combustible materials.
- Verified from the manufacturer or official document.
What this page does not establish
- No heater was measured for this page; thermostat duty cycles vary by room and are shown only as an assumption.
- Comparison with central heating depends on fuel and system and is not made here.
Sources
- Estimating appliance and home electronic energy use, Virginia Cooperative Extension. Calculation method; read 2026-09-07.
- Keep warm and safe this winter: tips for using generators, furnaces and space heaters, U.S. Consumer Product Safety Commission. Official guidance; read 2026-09-07.
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