It feels obvious that warming a single room must cost less than warming a whole house. Less space, less heat, smaller bill. In practice the answer turns on which fuel you burn, not how many doors you shut. Gas from your boiler is roughly a third of the price of electricity per unit, so a single 2kW electric heater can quietly cost more per hour than running the central heating that warms the entire ground floor. This guide works through the actual numbers at current UK prices so you can pick the cheaper option for your own home.
The short answer. Heating one room is usually cheaper only if you heat it with gas, or if you sit in that room for a short, defined period and switch everything else off. A single 2kW electric heater costs about 52p an hour at 26.11p per kWh, while a gas boiler firing flat out to heat a whole floor might burn 8 to 12kWh of gas, or roughly 60p to 88p an hour at 7.33p per kWh. The room wins when the heater is small, the run is short, and the rest of the house stays cold.
The fuel matters more than the floor area
The instinct to heat one room comes from thinking about space. Half the house, half the cost. That logic works only when both options use the same fuel. They usually do not.
Mains gas costs about 7.33p per kWh. Electricity costs about 26.11p per kWh. That is roughly three and a half times more for every unit of heat. So a plug-in electric heater starts the race a long way behind a gas radiator, even though it is warming a much smaller space.
This is the trap. People turn the central heating off, plug in a fan heater or an oil-filled radiator, and assume they are saving money because the boiler is silent. The boiler being off does cut gas use, but a 2kW or 3kW electric heater running for hours can cost more than the gas it replaced. Our guide to gas versus electric heating cost sets out the per-unit gap in full.
The honest version of the question is not "one room or whole house". It is "cheap gas heat across a floor, or expensive electric heat in one room". Once you frame it that way the maths gets clearer.
What each option actually costs per hour
Here is a like-for-like comparison at current UK prices. The gas figure assumes a typical combi boiler heating the ground floor of a three-bed house, cycling on and off so that it does not run at full input the whole time. The electric figures are for a single heater running continuously in one room.
| Heating choice | Energy used per hour | Cost per hour |
|---|---|---|
| Gas central heating, whole floor (boiler cycling) | ~8 to 12 kWh gas | 59p to 88p |
| One 1kW electric heater | 1 kWh | 26p |
| One 2kW electric heater | 2 kWh | 52p |
| One 3kW fan heater (flat out) | 3 kWh | 78p |
| Heating one room with the gas system (TRV zoning) | ~3 to 5 kWh gas | 22p to 37p |
At 7.33p per kWh gas and 26.11p per kWh electricity, Ofgem cap July to September 2026. Gas system run rates are estimates and vary with boiler size, insulation and how cold it is outside.
The pattern is clear. A 1kW electric heater (26p) does beat running the whole boiler (59p and up). But a 2kW heater is line ball with the boiler, and a 3kW fan heater costs about the same as heating a whole floor with gas. Meanwhile, heating a single room with the gas system by turning down the radiators elsewhere is the cheapest option of all.
The cheapest move: heat one room with gas, not electricity
If your house has gas central heating, the best of both worlds is to heat one room using the boiler rather than an electric heater. You keep the cheap fuel and you stop paying to warm rooms nobody is in.
You do this with thermostatic radiator valves. Turn the valves right down in the empty rooms and leave the valve open in the room you are using. The boiler still fires, but it has far less radiator surface to feed, so it burns less gas and reaches temperature faster. This is the same idea covered in turning radiators off in unused rooms.
A word of caution. Do not turn every other radiator stone cold all winter. Rooms that never get warm are prone to condensation and mould on the cold walls, and you may end up paying to fix that instead. Leave unused rooms ticking over at a low setting, around frost-protection to 14C, rather than fully off. Our notes on condensation and mould explain the trade-off.
Pair zoning with a sensible main thermostat. Setting it well is covered in thermostat settings and what temperature should I set my thermostat.
When a single electric heater really is cheaper
Electric room heating is not always the wrong call. It wins in specific situations.
- Short, defined sessions. If you only want heat for an hour or two in one room, say an evening at a desk, a small electric heater avoids firing up the whole boiler and warming pipes and radiators you will not benefit from.
- No gas, or gas is off. In a flat with electric-only heating, or a home where the boiler has failed, the comparison is electric against electric. Then the smallest heater that keeps you comfortable wins. See electric heater types compared.
- One person, one room, rest of the house empty. If you genuinely use a single room and leave the rest cold, a 1kW heater at 26p an hour is hard to beat.
The key is wattage and run time. A 1kW heater is cheap. A 3kW fan heater left on all evening is not. Match the heater to the job, and consider heating the person rather than the room. An electric blanket or a heated throw runs at well under 100W, which is a few pence an hour, and a portable heater guide helps you size the right unit.
The hidden costs of letting the rest of the house go cold
Heating one room and abandoning the rest is not free of downsides, and two of them can cost real money.
The first is reheating. If you let the whole house drop several degrees every day and then warm it back up, the fabric of the building (walls, floors, furniture) has to be reheated each time. For a poorly insulated home that swing can use more energy than holding a steady, lower temperature. This is the same debate as leaving the heating on all day, and the answer depends heavily on how well your house holds heat.
The second is damp. Cold, unheated rooms collect condensation, especially on outside walls and behind furniture. Mould remediation, ruined plaster and the health effects are a poor trade for a few pence saved. Keeping unused rooms gently warm and ventilated, as in ventilation without losing heat, avoids that.
Insulation changes the whole calculation. A well-insulated house holds heat for hours, so heating one room and closing the door keeps that room warm cheaply. A draughty house bleeds heat fast, so the single heater fights a losing battle. Cheap fixes like draught-proofing and heavier curtains make any heating strategy go further.
The bottom line
One room is not automatically cheaper. The fuel decides it.
- If you have gas central heating, the cheapest way to heat one room is to use the boiler and turn down the radiators elsewhere with TRVs. Cheap fuel, no wasted rooms.
- A single small electric heater (1kW) beats running the whole gas system, but a 2kW or 3kW heater often does not. Watch the wattage.
- Electric room heating wins for short sessions, for homes with no gas, and when you heat the person with a blanket or throw rather than the air.
- Do not let unused rooms go stone cold all winter. Damp and reheating costs can wipe out the saving. Keep them ticking over low.
For the bigger picture on what your heating actually costs to run, see cost of central heating per hour and the main home heating hub. If you are weighing up your boiler settings, dropping the boiler flow temperature on a condensing boiler is one of the cheapest efficiency wins available.