Space Heater Cost Calculator

About this calculator

Running cost is straightforward once you know three numbers: the heater's wattage, how many hours a day it runs, and your price per kilowatt-hour. The formula is watts ÷ 1000 × hours × days × price per kWh, since a kilowatt-hour is simply 1,000 watts drawn for one hour. Unlike central furnaces that cycle on and off to hold a room temperature, most portable space heaters run near full wattage the whole time they are switched on, which is what makes this a clean multiplication rather than a rough estimate.

People reach for this calculator when deciding whether zone heating a single occupied room with a plug-in heater is cheaper than warming the entire house with central heat, a common winter strategy for anyone working from home in one room or trying to avoid firing up a whole-house system overnight. It is also used to compare heater models — a 1,500-watt ceramic heater against a 750-watt oil-filled radiator — or to sanity-check an electricity bill spike after a heater has been left running for a season.