Electric Heat

Sizing resistance heat

Electric heat is the one heating system where sizing is straightforward: every watt in becomes a watt of heat, with no efficiency to argue about. The whole question is how many watts the room loses. Ten per square foot covers an insulated room with a standard ceiling in a moderate climate — the figure supply houses have used for decades — and the adjustments above are the three things that reliably break it: thin insulation, single glazing, and a genuinely cold winter.

Once you have watts, the shopping is mechanical. Baseboard element runs about 250 watts a foot, so the length follows directly. Divide watts by volts for amps, add 25 % because heat runs continuously, and you have the breaker. Almost anything over 1,500 watts should be wired at 240 volts — half the current, smaller wire, and no fighting over a shared circuit.

Where it goes

Under the window, along the outside wall. Cold air falls off the glass and pools on the floor; a heater in that path intercepts it and the room mixes on its own. The same heater on an inside wall heats the ceiling and leaves your feet cold. Split the total between two units if the room has two cold walls.

What it costs to run

Resistance heat is 100 % efficient and still the most expensive way to make heat, because electricity is the expensive energy. A 1,500 watt heater at 17 cents a kilowatt-hour costs about 26 cents an hour, or roughly $60 a month running twelve hours a day. That is the arithmetic that sends people to heat pumps — which move three units of heat per unit of electricity instead of making one.