Costs
7 min readAir conditioning against central heating
Per unit of heat, a modern air-to-air unit is cheaper to run than a gas boiler. That does not make it a replacement for one, and the difference matters more than the pence.
The short answer
Per unit of heat delivered, a modern air-to-air heat pump is cheaper to run than a gas boiler — roughly 6 to 7p a kilowatt-hour against about 8p, because it moves heat rather than making it and returns three to four times the energy it draws. That does not make it a replacement for central heating, and treating it as one is the mistake this comparison usually produces. A boiler heats every room and your hot water. An air-to-air system heats the rooms it is fitted in and does nothing for your taps. The honest comparison is not which is cheaper per kilowatt-hour but which is heating what, and when — and for most households the answer is that they are complementary rather than competing, with the heat pump earning its keep in the months when firing the whole house to warm one room is the expensive option.
They are not the same kind of machine
A gas boiler is a whole-house system with a single output: hot water, distributed to radiators and taps. An air-to-air heat pump is a per-room system that moves heat in either direction and never touches your water. Comparing their running costs without saying that first produces a number that is true and useless.
| Gas central heating | Air-to-air heat pump | |
|---|---|---|
| Heats | Every room with a radiator | Only the rooms with a head fitted |
| Hot water | Yes | No — nothing at all |
| Cools | No | Yes, the same unit |
| Efficiency | ~90% | 350–400% |
| Cost per kWh of heat | ~8p | ~6–7p |
| What that per-kWh figure hides | You are heating the whole house | You are heating one room |
That last row is the one that decides most of this. The heat pump wins on efficiency and the boiler wins on coverage, so the per-kWh comparison only means something once you have decided how much of the house you actually want warm. The arithmetic behind both figures, and the assumptions under them, are in what it costs to run rather than repeated here.
Where the heat pump genuinely wins
One room, some of the time. That is a narrower claim than most comparison pages make and it is the one that survives contact with a bill.
- The shoulder months. October and March, when one room is cold and the rest of the house is fine. Firing a boiler to warm a single room is the expensive way to solve that, and it is the case where the efficiency gap does real work.
- A room the heating never reaches properly. A loft conversion, a room over a garage, a north-facing study. These are the rooms where people already run a plug-in electric heater at four times the cost per unit of heat.
- Rooms used at odd hours. A home office at nine in the morning, a bedroom at eleven at night. Zoning a wet system that finely is expensive; a per-room unit is zoning by construction.
- Properties with no gas at all. If the alternative is direct electric — panel heaters, oil-filled radiators — the comparison is not close. Those run at about 25p a kilowatt-hour of heat against 6 to 7p.
Where the boiler still wins
Saying this plainly is more useful than the alternative, and it is most of why we are not going to sell you a system to replace your heating.
- Hot water. An air-to-air system does nothing for it. If you want a heat pump that replaces the boiler entirely, that is air-to-water, and it is a different machine at a different price — the comparison is here.
- Heating the whole house in January. Fitting enough indoor heads to warm every room is neither cheap nor sensible when a radiator circuit already exists.
- Deep cold. Efficiency falls as the outside temperature does. Below roughly −10°C you are closer to break-even with direct electric, which is the honest ceiling on the argument and is set out in full in the running-costs guide.
What it costs to find out
One room fitted is £1,895, or £2,395 with the pipework concealed. Two rooms on one outdoor unit is £3,795. Those are published prices rather than estimates, and what installation actually costs sets out what sits inside them and what legitimately changes them. There is also a £2,500 grant for air-to-air heat pumps, which excludes any property with fossil fuel heating — so if you have the gas boiler this comparison assumes, you almost certainly do not qualify. The grant, and who actually gets it.
If you want the arithmetic rather than the comparison, what it costs to run has the figures, the assumptions and the point at which they stop holding. If you want a price for a specific room, a few questions gets you a band without an email address.
Where this comes from
We’d rather you checked. These are the primary sources behind the claims above, in the order they matter.
- Manufacturer declared performance — current domestic rangesSeasonal efficiency figures for reverse-cycle wall splits from the Daikin, Mitsubishi and Toshiba domestic ranges.
- Ofgem energy price capSource for the electricity and gas unit rates the comparison assumes. Check the current cap before relying on any of it.
Not yet independently reviewed. This guide was written from the primary sources listed above and is accurate to the best of our understanding on the date shown. It hasn’t been checked by an independent compliance professional, and it isn’t legal advice. Where a decision turns on it, verify with your local authority or with Ofgem directly — and tell us if we’ve got something wrong.