Yes, in most homes you heat more cheaply with a split air conditioner than with gas. That is not magic, it is arithmetic. A gas boiler burns gas and gets about 90 percent useful heat out of it. An air conditioner burns nothing, but moves heat from outside to inside. For every kWh of electricity you get 3 to 4 kWh of heat back. That is called the COP.
To be concrete, using the prices of July 2026. A kWh of heat from gas costs you about 15.5 pence. That same kWh of heat from an air conditioner with a COP of 3.5 costs you about 7.7 pence. That is roughly half. Heat a room for a whole heating season with an air conditioner instead of gas, and that quickly adds up to anywhere from a few tens to a couple of hundred pounds, depending on how much you heat.
But watch out: cheaper is not the same as a full replacement system. An air conditioner heats the air in one room. No hot water from the tap, no heat in the room next door, and on the coldest winter days the COP drops sharply. For most people an air conditioner is therefore a smart addition to the central heating, not straight away the complete replacement.
Below I work it all out. The break-even point (from which COP you beat gas), a table with the cost per kWh of heat, and honestly the limits: cold days, hot water, noise, placement and maintenance.
Why is an air conditioner actually cheaper than gas?
It comes down to the difference between making heat and moving heat.
A boiler burns gas. Out of every m3 of gas comes a fixed amount of energy, and a bit of it is lost up the flue. A good condensing boiler gets about 90 percent useful heat out of it. A combustion boiler can never reach more than 100 percent. That is simply impossible physically.
An air conditioner is actually an air-to-air heat pump. It burns nothing. It uses electricity to pump a refrigerant round in a loop, and that refrigerant pulls heat out of the outside air (yes, even at zero degrees there is still heat in it) and brings it inside.
The beauty of it: for every kWh of electricity the air conditioner uses, it delivers 3 to 4 kWh of heat. That is an efficiency of 300 to 400 percent. Not because energy comes from nowhere, but because most of it comes free from the outside air. The electricity is only the “pump”.
That ratio between heat out and electricity in, that is the COP value. COP 4 means: 1 kWh of electricity in, 4 kWh of heat out. And that is exactly why an air conditioner can beat gas, even though electricity per kWh is more expensive than gas.
What is the difference between COP and SCOP?
Let me pull the two apart, because brochures often lump them together and that makes their figures look prettier than reality.
COP (Coefficient of Performance) is a snapshot. The efficiency at one particular outdoor temperature, usually measured at +7 degrees. Nice and mild. At +7 degrees a modern air conditioner easily reaches a COP of 4 or higher.
SCOP (Seasonal COP) is the average efficiency over a whole heating season. So including the cold days when your air conditioner has to work harder and is less efficient. The SCOP therefore always lies lower than the peak value from the brochure.
Why this matters: sellers love to boast about “COP 5!”. Sounds great. But that is at +7 degrees. For your annual bill the SCOP is what counts, and for a decent air conditioner that lies between 3.5 and 4.5. So in your own sums always work with the SCOP, not with the prettiest peak value. Below I deliberately work with a cautious SCOP of 3.5.
How much does a kWh of heat cost from gas versus from an air conditioner?
This is the heart of the whole story. To compare like with like, you do not work in “price per m3” against “price per kWh of electricity”. That is apples and oranges. You convert everything into price per kWh of useful heat. Only then do you honestly see what is cheaper.
Quickly, the building blocks (prices July 2026, all-in including tax and VAT):
- Gas price: about £1.36 per m3 (variable contract)
- Electricity price: about £0.27 per kWh (variable contract)
- Energy in 1 m3 of gas: 9.77 kWh
- Condensing boiler efficiency: about 90 percent
Converting gas to cost per kWh of heat:
Out of 1 m3 of gas comes 9.77 kWh of energy. At 90 percent boiler efficiency that leaves 9.77 x 0.90 = 8.79 kWh of useful heat. That m3 cost £1.36. So:
£1.36 / 8.79 kWh = £0.155 per kWh of heat from gas.
Converting the air conditioner to cost per kWh of heat:
The air conditioner uses 1 kWh of electricity (£0.27) and at a SCOP of 3.5 delivers 3.5 kWh of heat. Then:
£0.27 / 3.5 kWh = £0.077 per kWh of heat from the air conditioner.
Look at those two figures. 15.5 pence against 7.7 pence. At these prices the air conditioner is about half as expensive per kWh of heat. And that is with a cautious SCOP. Work with COP 4 and it gets even more favourable.
Table: cost per kWh of heat at different prices and COP
Prices move. That is why below is a table you can hold your own situation up against. Look up your electricity price and the COP of your air conditioner, and compare with the gas row underneath.
| Electricity price per kWh | COP 2.5 | COP 3.0 | COP 3.5 | COP 4.0 |
|---|---|---|---|---|
| £0.23 | £0.092 | £0.077 | £0.066 | £0.058 |
| £0.27 | £0.108 | £0.090 | £0.077 | £0.068 |
| £0.30 | £0.120 | £0.100 | £0.086 | £0.075 |
| £0.35 | £0.140 | £0.117 | £0.100 | £0.088 |
And the gas side, per kWh of useful heat (condensing boiler 90 percent):
| Gas price per m3 | Cost per kWh of heat |
|---|---|
| £1.20 | £0.137 |
| £1.36 | £0.155 |
| £1.50 | £0.171 |
| £1.70 | £0.193 |
Here is how to read it: if your air conditioner figure in the top table is lower than your gas figure in the bottom one, then you heat more cheaply with the air conditioner. In almost every row that is the case. Only with an expensive electricity price (£0.35) combined with a low COP (2.5) and a cheap gas price (£1.20) do they come close to each other.
Where exactly is the break-even point?
A handy rule of thumb to remember, so you can always check it yourself.
The air conditioner is cheaper as soon as:
COP greater than (electricity price / gas cost per kWh of heat)
With today’s prices: £0.27 / £0.155 = 1.74.
That means: as long as your air conditioner reaches a COP of more than about 1.74, you heat more cheaply than with gas. A modern split air conditioner in winter is almost always above 2.5, often above 3. So you have a hefty margin.
Only when it really freezes hard and the COP drops below 1.7 to 2 does gas come close. And even then it is usually a draw, not a big loss. More on that in a moment, because those cold days are exactly where the nuance sits.
When is an air conditioner NOT cheaper or not practical?
Now the honest part. Because “cheaper per kWh” is not the whole story. There are situations where it delivers less or simply does not work.
On severe frost days the COP drops. The colder it is outside, the harder the air conditioner has to work to pull heat in. At -5 or -10 degrees the COP can fall back to 2 or even lower. On top of that the outdoor unit has to defrost now and then, and during that defrost it delivers no heat for a while. In those coldest weeks of the year the advantage melts away to a draw with gas. Good news: those are only a handful of days a year.
No hot water. This is the big one. An air conditioner heats air, not water. For your shower, your tap and your bath you therefore still need something: your boiler, or a separate water heater. On this point an air conditioner simply does not replace your boiler.
One unit heats one room. A split air conditioner blows warm air into the room where the indoor unit hangs. The bedroom upstairs, the bathroom, the hallway: those stay cold. If you want more rooms, you need several indoor units (a multi-split) and that costs more to buy and to run.
Poorly insulated house. In a draughty house with single glazing and cold walls every heating system has to fight, the air conditioner included. The heat leaks away faster than you blow it in, the air conditioner runs at full load and precisely then its efficiency drops. Insulate first, then count on big savings.
Dynamic or expensive electricity contract. Work with your real electricity price. If you are on an expensive variable tariff above £0.30 and have an older air conditioner with a mediocre COP, then the advantage gets small. If you have solar panels or a dynamic contract with cheap hours, then it becomes extra attractive.
Bluntly put: as a replacement for your whole central heating a single air conditioner is usually too limited. As a smart addition for your living room, where you spend the most hours, it is almost always a winner.
Step-by-step: work out your own break-even
Want to know exactly what it does in your home? Follow these steps. Grab your last energy bill.
- Find your gas price per m3 on your contract or annual statement. All-in, so including tax and VAT.
- Convert gas to cost per kWh of heat. Divide your gas price by 8.79. (That is 9.77 kWh per m3 times 90 percent boiler efficiency.) Example: £1.36 / 8.79 = £0.155.
- Find your electricity price per kWh, also all-in.
- Pick a realistic SCOP. For a modern split air conditioner: 3.5. Cautious? Take 3.
- Convert the air conditioner to cost per kWh of heat. Divide your electricity price by the SCOP. Example: £0.27 / 3.5 = £0.077.
- Compare the two. If step 5 is lower than step 2, then the air conditioner is cheaper. The difference is your saving per kWh of heat.
- Estimate your heat demand. Do you mainly heat the living room? Reckon roughly on 8 hours a day, about 1 to 1.5 kWh of heat per hour, over a heating season of 150 to 180 days. That is roughly 1,500 to 2,700 kWh of heat for that one room.
- Multiply the difference by your heat demand. A difference of £0.078 per kWh times 2,000 kWh of heat = about £156 saved per heating season, for that one room.
This is an estimate, not a law. Your heating habits, your insulation and how harsh the winter is decide the real figure. But it gives you an honest order of magnitude, and that is more than most brochures give you.
What does buying it cost, and do you earn that back?
A single split air conditioner (good quality, including installation) costs roughly £1,500 to £2,500. A multi-split with several indoor units runs higher.
Save around £150 to £300 per heating season on your one living room, plus keep a free air conditioner in summer for those few hot weeks, and your payback time lands somewhere between 6 and 12 years on the heating alone. Count in the cooling and the comfort, and it feels worthwhile sooner.
Note: for an air-to-air air conditioner you generally get no grant, whereas for a “real” (air-to-water) heat pump you can get one. That is a difference to weigh up if you are torn between the two.
How much noise does an air conditioner make, and where can the outdoor unit hang?
Two practical things people often forget until it is too late.
Noise. The indoor unit hums about like a soft fan, usually no problem. The outdoor unit is the thing to watch, especially in winter when it runs hard and defrosts now and then. For yourself it is manageable, but your neighbours can be bothered by it. Many councils have a noise limit for the outdoor unit at the neighbours’ property boundary: in the evening and at night (7pm-7am) a maximum of about 40 dB, and during the day (7am-7pm) a maximum of about 45 dB. Check the exact figures with your local council. In any case, do not hang the outdoor unit right under the neighbours’ bedroom window.
Placement and permission. For an outdoor unit on an ordinary house you usually do not need permission, provided you meet the noise standard and the rules for placement. If you live in a listed building, a conservation area, a flat or under a leasehold or residents’ association, then there are often extra requirements or you need consent. Check that beforehand with your council or association. Saves hassle afterwards.
How much maintenance does an air conditioner cost?
Little, but not zero. And this belongs in your sums, because brochures like to leave it out.
The filters of the indoor unit you have to clean yourself a few times per heating season. Dirty filters cost efficiency and therefore money. That is a five-minute job, free.
On top of that, periodic maintenance by a professional is sensible, every one to two years. They check the refrigerant, the pressure and the operation. Reckon on about £75 to £150 per visit. For a fair comparison with gas that is honest: your boiler needs maintenance too, so those cancel each other out. But do not write it off as though an air conditioner is completely maintenance-free.
Air conditioner or keep the boiler after all?
For most existing homes the answer is: both. A hybrid approach.
You use the air conditioner for the daily heating of the rooms where you sit most, the living room first. There it runs cheaper than gas for the biggest part of the heating season. You keep your boiler for the hot water and for those few severe frost weeks when the air conditioner has a hard time.
That way you grab the best of both worlds: the low heating costs of the air conditioner on mild days, the certainty of the boiler on the coldest days and for your shower. For many people that is the most level-headed choice, without an expensive full renovation.
Frequently asked questions
Is heating with an air conditioner really cheaper than with gas?
Yes, in most cases. At the prices of July 2026 a kWh of heat from gas costs about 15.5 pence and from an air conditioner with COP 3.5 about 7.7 pence. That is roughly half. Only with an expensive electricity price, a low COP and a cheap gas price do they come close to each other.
Does an air conditioner still work when it freezes?
Yes, modern air conditioners heat well below zero. But the colder it gets, the harder the unit has to work and the lower the COP. On severe frost days (-5 degrees and colder) the efficiency drops and the cost advantage melts away to a draw with gas. Those are only a handful of days a year.
Can an air conditioner replace my boiler completely?
Usually not on its own. An air conditioner heats air in one room and makes no hot water. For your shower and tap, and for the rooms without an indoor unit, you still need something. For many people an air conditioner is therefore an addition to the central heating, not a complete replacement.
What COP or SCOP do I need to save money?
With current prices you are already cheaper off than gas as soon as your air conditioner reaches a COP of about 1.74. A decent split air conditioner in winter is almost always above 2.5, often above 3. So you have plenty of margin. For your annual bill work with the SCOP (the seasonal average), not with the prettiest peak value from the brochure.
Do I get a grant for an air conditioner as heating?
Generally not. An air-to-air air conditioner usually falls outside the grant schemes, whereas a real air-to-water heat pump can get one. Weigh that up if you are torn between the two.
What does maintaining an air conditioner cost?
The filters you clean yourself a few times per season, free. Periodic maintenance by a professional every one to two years costs about 75 to 150 pounds. That roughly cancels out against the maintenance of a boiler, so in a fair comparison it barely plays a role.
An air conditioner that heats cheaper than your boiler is nice, but it is one move on a much bigger board. The real win on your energy bill often sits in the combination: heating smartly, insulating well and tackling the hidden power drains you do not see.
I have put everything I know about getting your bill down in one place, in the energy-saving guide on the Energy Crusher. Concrete steps and real figures, no vague chatter. Have a look around: energie-verpulveraar.fredsbouwtekeningen.nl