Short answer: a 1,500-watt space heater costs about 27 cents for every hour its heating element is actually on, at an electricity rate of 18.2 cents per kWh. Run flat out for 8 hours, that is about $2.18. Because most heaters have a thermostat that switches the element on and off, your real cost depends on how much of that time the heater is actually drawing power.
The formula for any space heater
Three units get mixed up on every bill, so keep them apart: watts measure how fast a device uses power, kilowatt-hours (kWh) measure the energy it used over time, and dollars are kWh multiplied by your rate.
Cost = (watts ÷ 1,000) × hours the heater is on × your rate per kWh
Your rate is on your bill (look for the price per kWh, or divide the electricity charges by the kWh used). If you are unsure, our step-by-step bill guide shows where to find it.
Worked example with a stated rate
For the national picture, the U.S. Energy Information Administration's October 2026 Short-Term Energy Outlook projects an average residential price of 18.2 cents per kWh for 2026 (EIA). We use $0.182 below. Your utility's rate will differ, so substitute your own.
- 1,500 W ÷ 1,000 = 1.5 kW
- 1 hour on: 1.5 kW × 1 h = 1.5 kWh × $0.182 = $0.27
- 8 hours on, nonstop: 12 kWh × $0.182 = $2.18
- 8 hours a day for 30 days, nonstop: 360 kWh × $0.182 = $65.52
Rates vary a lot by state, so here is the same heater at three example rates:
| Rate per kWh | Cost per hour on | 8 hours on |
|---|---|---|
| 12¢ (low-rate area) | $0.18 | $1.44 |
| 18.2¢ (U.S. average, EIA 2026 projection) | $0.27 | $2.18 |
| 30¢ (high-rate area) | $0.45 | $3.60 |
Many heaters also have a low setting around 750 W. That uses half the power, so it costs half as much per hour on, though it also delivers half the heat.
How thermostat cycling changes the real cost
A resistance heater draws its full rated power while the element is on and almost nothing while it is off. The thermostat does not make the heater "use less power" at any moment. It changes the share of time the element is on, called the duty cycle. Cost scales directly with that share:
Real cost = 1.5 kW × hours of use × duty cycle × rate
Same heater, same rate: the share of time the element is on sets the cost.
The chart uses four example duty cycles for an 8-hour evening. These are illustrations, not measurements of any particular room.
| Duty cycle | kWh in 8 hours | Cost (8 h) | Cost (30 days) |
|---|---|---|---|
| 100% (never reaches set point) | 12.0 | $2.18 | $65.52 |
| 60% | 7.2 | $1.31 | $39.31 |
| 40% | 4.8 | $0.87 | $26.21 |
| 25% | 3.0 | $0.55 | $16.38 |
Which row you land in depends on the room: how cold it is outside, how well the room is sealed and insulated, how big it is, and how high you set the thermostat. A small, sealed room that is already close to the set point spends more time off. A large or drafty room can keep the element on nearly all the time. A heater with no thermostat is effectively at 100% until you switch it off.
Measure your own heater in one evening
- Plug a plug-in watt meter into the wall outlet, then plug the heater into the meter. Reset the kWh reading.
- Run the heater the way you normally would for a few hours and note the elapsed time.
- Read the kWh total. Your cost is kWh × your rate. Divide kWh by (1.5 × hours) to get your actual duty cycle.
Example: 4.2 kWh over 7 hours at $0.182 is $0.76, and 4.2 ÷ (1.5 × 7) = 0.40, so the element was on about 40% of the time.
When a space heater actually saves money
A space heater only lowers your bill if it replaces heat you would otherwise pay for. That generally means lowering the central thermostat while you heat only the room you are using. If you add a space heater and leave the whole-house setting alone, you pay for both. Ask three questions: Is the central thermostat turned down? Will you be in that room for most of the hours? Does the measured kWh cost less than the heating you are skipping? You can check the third with the measurement above and your central heating cost per kWh or therm.
Safety basics
A 1,500 W heater on a 120-volt outlet draws about 12.5 amps (1,500 ÷ 120), a heavy load for one circuit, so do not share the outlet with other high-draw devices. The U.S. Consumer Product Safety Commission advises keeping flammable materials at least three feet away, plugging space heaters directly into a wall outlet rather than a power strip, and not leaving them running unattended in a confined space (CPSC).
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