Understand it · practical guide
Is it cheaper to heat one room? The honest answer
In one line: The space-heater maths works - for one person, in one room, for a few hours. Here is where the boundary sits, and why 'turn off the heating and huddle' can cost more than it saves.
The question arrives every winter with the first cold week: leave the heating off and run a 1,500 W space heater in whichever room you are in - or heat the whole house? The honest answer has a narrow true zone, and most households drift outside it without noticing.
Where the space heater genuinely wins
The heater draws 1.5 kW, so each hour costs one-and-a-half times your rate per kWh - around 27 cents at an average US rate, 40p at the UK cap rate. If you would otherwise heat the whole house for those hours, one occupied room at 27-40 cents an evening-hour is dramatically cheaper, because the alternative is heating rooms nobody is in. The win zone: one or two people, one room, a few hours, doors closed - the classic evening in the sitting room while the bedrooms stay cold until bedtime.
Where the maths turns
Three drifts erase the saving. Time: run the heater all day, or in two rooms, and its total approaches or passes what the central heating would have cost for the same comfort. Fuel: electric resistance is the most expensive heat per unit there is - if your central system is a heat pump or a gas boiler, one electric heater's "cheap" evening can cost more than hours of the whole-house system it replaced. Damp: a permanently cold house accumulates condensation and mould on cold walls, and that repair dwarfs any heating saving - the moisture chain runs through ventilation that works and paint that survives damp rooms.
The hybrid that actually saves
Use the heater for the sharp edges of the day - the morning kitchen, the evening sitting room - and let the central system hold a lower background temperature so the house never gets genuinely cold. That is the setback principle from the thermostat guide with a heater filling the peaks, and it is how the one-room trick keeps its maths honest. Support it the boring way: doors closed on the heated room, curtains closed on the dark side of the house, and the fan on winter mode pushing warm air back down. If the whole house needs heat all day anyway, the space heater is only adding an expensive layer - the real levers are insulation and draughts, which cut the bill at every setting.
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General information, not professional advice. Homes differ — if a job is beyond your confidence or the guide’s boundary, that is what tradespeople are for.