Space heaters are a cheap way to warm one room, but they can add a surprising amount to your electric bill if they run all day. The good news: the cost is easy to calculate.

The formula

cost per hour = watts ÷ 1,000 × your rate per kWh

Most plug-in space heaters top out at 1,500 watts, which is 1.5 kWh per hour on full power. Your electricity rate is on your bill, shown in cents or dollars per kWh.

A worked example

Take a 1,500-watt heater running 8 hours a day, at an example rate of $0.17 per kWh:

• Per hour: 1.5 kWh × $0.17 = about $0.26
• Per day (8 hours): 12 kWh × $0.17 = about $2.04
• Per month (30 days): about $61

Rates vary a lot by state and plan, so plug in your own numbers with our Electricity Cost Calculator.

Why real costs are often lower

Heaters with a thermostat switch off once the room reaches the set temperature, then cycle back on. In a well-insulated room, a heater may run at full power only part of the time. Using the low setting (often around 750 to 900 watts) also cuts the cost roughly in half.

When a space heater saves money

All electric resistance heaters turn electricity into heat at about the same efficiency, whatever the marketing says. A space heater saves money when it lets you turn the central thermostat down and heat only the room you’re using. If it’s running alongside a fully heated house, it simply adds to the bill.

Safety rules

• Plug it directly into a wall outlet. Avoid extension cords and power strips; they can overheat.
• Don’t share the circuit with other big loads. At 1,500 watts on 120 volts, a heater draws about 12.5 amps, most of a standard 15-amp circuit.
• Keep 3 feet of clearance from curtains, bedding, furniture and anything that can burn.
• Choose models with tip-over and overheat shutoff, and never leave one running unattended or while you sleep.

If the plug or outlet gets hot, or breakers trip when the heater runs, stop using it and have the circuit checked. Our guide on when to call an electrician lists the warning signs.

Key takeaways

• Cost per hour = kW × rate; a 1,500 W heater uses 1.5 kWh per hour on high.
• It saves money only if you lower heat in the rest of the house.
• Plug directly into the wall and keep clearance around it.