Air Conditioning vs Electric Heaters: Which Heats a Room for Less?
Why air conditioning in heating mode typically needs about a third of the electricity of a plug-in heater, explained in under a minute.
The short answer
- An electric heater (panel, oil-filled, fan or storage) turns each unit of electricity into one unit of heat.
- Air conditioning in heating mode is an air-to-air heat pump. It moves heat in from outdoors, typically delivering about three units of heat for every unit of electricity it uses.
- So for the same warmth it uses roughly a third of the electricity of an electric heater, and on the same tariff roughly a third of the running cost: a bit more in a hard frost, less on a mild day.
Why an electric heater can’t do better than one-for-one
Every electric heater works the same way inside: current runs through a resistance element and the element gets hot. Almost all of the electricity ends up as heat in the room, which is why these heaters are often described as 100% efficient. That sounds unbeatable, but it is also the ceiling: one unit of electricity in, one unit of heat out.
A kilowatt-hour on your bill is called a “unit”. A 2 kW heater running for a five-hour evening uses 10 units, and gives you 10 units of heat.
Storage heaters are no different in this respect. They buy their electricity at a cheaper off-peak rate and release the heat later, which can lower the cost, but the energy arithmetic is still one-for-one.
How air conditioning heats: moving heat instead of making it
A modern split air conditioner is reversible. In heating mode it runs as an air-to-air heat pump: rather than turning electricity into heat, it uses electricity to carry heat that is already in the outdoor air into your room. Moving heat takes far less energy than making it, and that is where the saving comes from.
- 1
The outdoor unit gathers heat. A refrigerant that boils far below freezing runs through the outdoor coil. Even on a frosty day the outside air is warmer than the refrigerant, so the refrigerant soaks up its heat and evaporates.
- 2
The compressor squeezes it hotter. Compressing the refrigerant gas raises its pressure, and with it its temperature, to well above room temperature.
- 3
The indoor unit releases it. The hot refrigerant flows to the wall-mounted indoor unit, where a fan blows room air across the coil and the refrigerant gives up its heat.
- 4
The cycle repeats. An expansion valve drops the pressure again, the refrigerant turns cold, and it heads back outside for more.
In summer, a valve reverses the flow and the same system carries heat the other way, out of your room, to keep you cool. For more on the refrigerant cycle, see how air-to-air heat pumps work.
What “about three units of heat” means
The ratio of heat delivered to electricity used is called the coefficient of performance, or COP. An electric heater’s COP is 1. For air conditioning in heating mode, GOV.UK’s guidance on air-to-air heat pumps puts it at about three units of heat for every unit of electricity, and the Energy Saving Trust puts them at about three times as efficient as standard electric heaters.
Because the ratio changes with the weather, product labels quote a seasonal figure, the SCOP, measured in a standard test over a typical heating season. Modern wall-mounted systems are typically rated at a SCOP of about 4 to 5 in that test, and the law sets a minimum of 3.8 for the refrigerant they use. Real homes usually see noticeably less than the label, because of colder spells, defrosting, and how a system is sized and used. That is why “about three” is the honest everyday figure.
| Outside | Heat for each unit of electricity |
|---|---|
| Mild, 7 to 10 °C | about 4 |
| Around freezing, 0 to 5 °C | about 3 |
| Hard frost, around −5 °C | about 2 to 2.5 |
| Any electric heater, any weather | 1 |
Illustrative figures for a modern wall-mounted system. The real ratio depends on the model, how it is sized and installed, and how it is used.
What that means for your electricity use
Take a living room that needs 1,500 kWh of heat over a winter, roughly a 2 kW heater running five hours a day for five months.
Plug-in electric heater
1,500 kWh
of electricity: about £395
Air conditioning, heating
about 500 kWh
of electricity: about £132
Both costs use the Ofgem price cap rate for October to December 2026: 26.32p per kWh, paying by direct debit, as a Great Britain average. The air conditioning figure assumes the typical three units of heat for each unit of electricity; in a colder winter it could be nearer 600 kWh (about £158). These are unit costs only: your standing charge is the same either way. Prices change every quarter; the difference in the electricity used does not.
The comparison assumes the same tariff for both. If you heat with storage heaters on an off-peak tariff, the cost gap is narrower than the energy gap, although air conditioning still uses far fewer units.
Does it still work when it’s freezing?
Yes. Air well below freezing still holds heat that a refrigerant can pick up, and modern systems keep heating in temperatures well below zero; the working limit depends on the model, commonly around −15 °C to −20 °C.
Efficiency does fall as it gets colder, and in frosty weather the outdoor unit pauses for a few minutes now and then to defrost its coil. Even so, it still delivers more heat for each unit of electricity than an electric heater.
When a plug-in heater still makes sense
Air conditioning isn’t the answer for every room. A plug-in heater costs little to buy and is fine for a room you heat for an hour or two a week. An air-to-air system also heats the air in the room, not your hot water, so it works alongside whatever heats your water now.
Where it makes most sense is the rooms you heat every day, such as living rooms, bedrooms and home offices, and again in summer, when the same system cools them.
Transcript
Here are two ways to heat a room with electricity.
A plug-in heater turns one unit of electricity into one unit of heat. One in, one out.
Air conditioning is smarter. In heating mode, it’s an air-to-air heat pump. It doesn’t make heat — it moves it.
Even frosty air holds heat. The outdoor unit gathers it, a compressor squeezes it hotter, and the indoor unit breathes it into your room.
So for every unit of electricity, you get about three units of heat. A bit less in a hard frost, more on a mild day.
The same cosy room, for roughly a third of the electricity.
And in summer, the same system keeps you cool.
Arctic Air Conditioning. Warm in winter, cool in summer.
Frequently asked questions
Is air conditioning cheaper to run than an electric heater?
For heating the same room on the same electricity tariff, usually yes. An electric heater gives one unit of heat for each unit of electricity; air conditioning in heating mode typically gives about three, so it uses roughly a third of the electricity for the same warmth. The exact figure depends on the model, the installation, the outdoor temperature and how you use it.
Is air conditioning an air-to-air heat pump?
A reversible air conditioner is an air-to-air heat pump: it heats a room by moving heat in from outdoors, and cools it by moving heat out. That is different from an air-to-water heat pump, which replaces a boiler and heats radiators and hot water. Arctic AC fits air-to-air systems: wall-mounted split, multi-split and ducted air conditioning.
What does SCOP mean on an air conditioner?
SCOP is the seasonal coefficient of performance: the heat a system delivers over a standard heating season divided by the electricity it uses. A SCOP of 4 means four units of heat for each unit of electricity in that test. Real homes usually see noticeably less than the label; about three is typical.
Does air conditioning work for heating in a UK winter?
Yes. Modern systems keep heating well below freezing, commonly to around −15 °C or lower depending on the model. They work less efficiently the colder it gets, and pause briefly now and then to defrost in frosty weather, but they still give more heat for each unit of electricity than an electric heater.
Can air conditioning heat my hot water?
No. An air-to-air system heats and cools the air in the rooms it serves. Your hot water stays with your existing boiler, cylinder or immersion heater.
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