How much does it cost to run a space heater?

The arithmetic

Electric resistance heaters turn all the electricity they use into heat, so their cost is simply power × hours × price. Most plug-in heaters have a top setting of 1,500 W and a lower one; the U.S. Department of Energy’s appliance calculator uses 1,320 W for a space heater. At the top setting an hour is 1.5 kWh: at 15¢ a kWh, about 23¢ an hour; at 30¢, 45¢.

The price per kWh is where states and plans differ. Below, each state is priced on the cheapest plan open to any household from its largest utility modeled on HomeWattCost (the state’s average price where no utility is modeled), at the price that applies on a January weekday, a winter month, including any tier the typical home’s January use reaches.

A month of evenings

A heater left on 4 hours every evening from 6 pm, at 1,320 W, uses about 5.3 kWh a day and 164 kWh over January. Priced on the whole bill, so that the extra kWh land in the right tier and the right period, that adds a median $26 to the January bill across the states, from $13 to $112. The 4-hour evening is an example; the cost scales with your own hours.

Does the hour matter?

Only on a time-of-use plan. On 13 of the 51 plans here, the January price at 7 pm is higher than at 2 am, by up to 34.7¢ a kWh. On a flat or tiered plan a kWh costs the same at any hour, and the only lever is how long the heater runs. If you are on a time-of-use plan, the peak window is the expensive time to use a heater; the off-peak hours table shows each plan’s winter peak.

When a space heater makes sense

A space heater heats one room, so it can cost less than raising the whole house’s thermostat when only one room is in use. As a way to heat the whole house it is expensive: resistance heat turns one kWh into one kWh of heat, while a heat pump delivers two or more (see heat pump vs gas, state by state). The saving, if any, comes from turning the central heating down while the heater warms the room you are in.

• Use the low setting and the thermostat. The cost per hour falls in proportion to the power; a heater with a thermostat cycles off once the room is warm.
• Plug it straight into a wall outlet. Fire-safety agencies advise against extension cords and power strips for space heaters, and keeping anything that can burn well away from them.
• Know your plan. On a time-of-use plan, avoid the winter peak; on a tiered plan, a heater can push the month into a dearer tier. The appliance cost calculator prices any wattage and schedule on your utility’s actual plan.

Not included here: the gas or electric heating the space heater may let you turn down, and sales taxes on the bill. The methodology describes how plans and the typical home are modeled.