Air-to-air heat pumps: the air conditioner that heats your home
Here's a piece of terminology worth thirty seconds of your time, because it reframes what you're buying: a modern split-system air conditioner and an air-to-air heat pump are the same machine. One name emphasises the summer job, the other the winter job. The unit moves heat between inside and outside using a refrigeration cycle, and a reversing valve decides which direction. If you're pricing up "air conditioning" for a UK home, you're almost certainly pricing an air-to-air heat pump — and thinking of it that way changes the value-for-money maths completely.
Why the heating side is the quiet bargain
Because a heat pump moves heat rather than generating it, it typically delivers around three or more units of heat per unit of electricity in UK conditions (a "COP" of 3+). A plug-in electric heater delivers exactly one. At ~26p/kWh, that's the difference between roughly 8–9p and 26p per kWh of heat — which is why heating a home office or living room through a split unit usually undercuts electric heaters decisively, and competes well against gas for single-room, on-demand heating. If you work from home, the winter savings alone can carry a large slice of the installation cost, with summer cooling effectively thrown in.
Air-to-air vs air-to-water: don't confuse the two
| Air-to-air (this article) | Air-to-water | |
|---|---|---|
| What it does | Heats and cools the air in rooms directly via indoor units | Heats water for radiators/underfloor and hot water cylinder |
| Cooling in summer | Yes — it's an air conditioner | Generally no (rare exceptions) |
| Replaces your boiler? | No — no hot water; whole-home heating needs a unit per zone | Yes — full boiler replacement |
| Typical installed cost | £1,500–£3,500 per room; multi-split £3,500–£6,000+ | £7,000–£15,000+ whole-house |
| Government grant | No — not eligible | Boiler Upgrade Scheme (£7,500 in England & Wales) |
| Disruption | Half a day to a day per room | Days; may need radiator and cylinder changes |
The grant line surprises people: the Boiler Upgrade Scheme does not cover air-to-air heat pumps, because they don't provide hot water and aren't a full boiler replacement. If a salesperson implies grant money on a split-system install, that's a red flag. The flip side: without the grant machinery, air-to-air installs are faster, cheaper per room, and don't require committing your whole heating system to one decision.
When air-to-air is the right call
- You want cooling anyway. If summer comfort is on the list, air-to-air is the only heat pump that does both — an air-to-water system solves winter and leaves July exactly as it found it.
- Room-by-room heating suits your life. Home office by day, living room by evening — heating occupied rooms on demand beats heating the whole house, and beats it hardest for people at home all day.
- Your gas boiler is fine for now. A split system doesn't ask you to remove anything. Many households run the boiler less each winter as the splits take over the rooms they live in — a low-risk, incremental route to lower-carbon heating.
- Flats and homes where wet-system upheaval isn't viable — subject to the consent points in our flats guide.
When it isn't: if your goal is replacing a boiler outright, including hot water, with grant support — that's the air-to-water conversation, a different project with different installers.
Costs, rules and sizing
Installation prices, what's in a quote and how to judge one are in our cost guide; per-hour heating and cooling costs in the running costs guide. Planning-wise, the May 2025 permitted development changes were written for exactly these units — reversible air-to-air systems on houses generally need no application (full rules here). Sizing works the same as any split: run your room through the calculator, and note that a unit sized for summer cooling is usually adequate for that room's winter heating in a reasonably insulated home — your installer's survey confirms it.
Thinking year-round comfort rather than just surviving July? Get free quotes from certified installers and ask them to spec the system for heating as well as cooling — same hardware, better conversation.
Quick answers
Do air-to-air heat pumps work in cold UK winters?
Yes. Modern units heat effectively well below freezing; efficiency falls as it gets colder but stays comfortably above electric heaters at any temperature a UK winter will realistically serve. Check the unit's rated heating output at -7°C if you're buying primarily for winter.
Can air-to-air heat pumps replace central heating completely?
They can heat every room if you fit enough indoor units (a multi-split), but they don't heat water — you'd keep a cylinder with an immersion or another hot-water solution. Most UK households use them as room-level heating alongside an existing boiler rather than a wholesale replacement.
Why is there no grant if they're heat pumps?
The Boiler Upgrade Scheme funds replacing fossil-fuel boilers with systems that provide space heating and hot water — air-to-water and ground source. Air-to-air units don't do hot water, so they sit outside the scheme's scope. Their lower install cost partly compensates.