How much does a space heater actually cost to run?

A plug-in heater's running cost is easier to work out than most people expect. Take the wattage, divide by 1,000 to get kilowatts, then multiply by the hours you run it and your electricity rate. A 1,200W unit run for four evening hours at 17 cents per kWh costs roughly 82 cents.

That number only matters next to the alternative. Raising a whole-house thermostat by three degrees warms hallways, spare bedrooms and the stairwell you walk through twice a night. Spot heating skips all of it, which is where the savings actually come from — not from the heater being magically efficient. Every resistive heater converts essentially all the electricity it draws into heat.

Two habits cut the bill further. First, run the heater on its thermostat rather than full blast: once the room reaches temperature, the element cycles instead of drawing peak power continuously. Second, close the door. A warm room with an open door is a warm hallway with an expensive room attached.

If you are heating the same room every night for months, compare the seasonal cost with a small efficiency upgrade — a draught excluder under the door, or thermal curtains. Both make any heater, at any price, do less work for the same comfort.