Cost to Run an Electric Heater: Space Heater and Baseboard Calculator

The formula

Electric resistance heat is the simplest load in the house: current flows through a resistive element and every watt becomes heat in the room. Whether it is a ceramic cube, an oil-filled radiator, a quartz infrared panel or a baseboard strip, a 1,500 W heater delivers 1,500 W of heat.

kWh per day = Watts × Duty fraction × Hours on ÷ 1,000
Cost = kWh × Rate ($/kWh)
Heat output (BTU/h) = Watts × 3.412

The duty fraction accounts for the built-in thermostat. Once the room reaches the set temperature, the heater cycles off and on, so in a well-insulated room it may only draw power half the time. In a cold, drafty room it may never cycle off.

Worked example

With the calculator defaults, a 1,500 W heater running at full power for 6 hours a day at $0.17/kWh:

1. Energy per day: 1,500 × 1 × 6 ÷ 1,000 = 9 kWh
2. Cost per day: 9 × $0.17 = $1.53
3. Over 30 days: 270 kWh, about $45.90 a month
4. Cost per hour on high: 1.5 kW × $0.17 ≈ $0.26

If the thermostat cycles it half the time, the monthly cost falls to about $23. Heat output on high is 1,500 × 3.412 ≈ 5,100 BTU/h, enough to take the chill off one room but well short of the 30,000–60,000 BTU/h a whole house needs on a cold day.

Cost per hour by heater type

At $0.17/kWh, running at full power:

Oil-filled and infrared heaters often feel different (gentler heat, or warmth on your skin rather than the air), and that can let you run them at a lower setting. Their efficiency is identical.

How many watts does a room need?

A common rule of thumb for supplemental electric heat is about 10 W per square foot of floor area in a room with average insulation and an 8-foot ceiling. By that measure, a single 1,500 W heater handles roughly 150 sq ft, which matches the label claims on most plug-in units. Poorly insulated rooms, rooms over unheated garages and rooms with lots of glass can need 12–15 W per square foot; well-insulated modern rooms may need only 6–8.

If one heater can't keep up, two smaller heaters on separate circuits are safer than chasing a bigger load on one outlet. For anything beyond a single room, the heating BTU calculator estimates the full load, and the BTU conversion calculator converts between BTU/h and watts.

Electric heater vs heat pump

A heat pump moves heat instead of making it, so it delivers two to four times more heat per kWh. At a COP of 2.5, the same 5,120 BTU/h that a 1,500 W heater produces takes only 600 W, about $0.10 an hour instead of $0.26. For whole-home heating the difference is hundreds of dollars a month in winter; see the heat pump running cost calculator and gas vs electric heating.

Where a space heater does make sense is zone heating: warming one occupied room while the rest of the house is kept cooler. If that lets you turn the central thermostat down several degrees, the total bill can fall. If you run space heaters on top of an unchanged central setpoint, you are adding cost. To estimate a whole-house heating bill, use the heating cost calculator.

Space heater safety

A 1,500 W heater draws about 12.5 A at 120 V, close to the limit of a standard 15 A circuit. Plug it directly into a wall outlet, never into an extension cord or power strip, and don't share the circuit with another large load such as a microwave or hair dryer. Keep 3 ft of clearance from bedding, curtains and furniture, choose a model with tip-over and overheat shutoff and a recognized safety listing, and never leave it running unattended or while sleeping unless it is designed for that. A warm plug or outlet means a poor connection: stop using it and have an electrician check the outlet.

Hard-wired baseboard, wall heaters and electric furnaces run on 240 V circuits. Installing or rewiring them is a job for a licensed electrician.

Getting more warmth for the same watts

• Heat the person, not the room. A heated blanket or a small radiant panel near a desk uses a fraction of the energy of heating the whole room.
• Close the door to the room you are heating so the warm air isn't drawn off to the rest of the house.
• Seal drafts around windows and doors; a drafty room can keep a heater running at full power.
• Use the heater's thermostat or a plug-in thermostat rather than leaving it on high.

To compare with other household loads, see average electricity usage by appliance.

Frequently asked questions