Air Source Heat Pump Guide: Cost After Grants, How It Works and What Installation Involves

Around 250,000 heat pumps went into UK homes in 2025 — a record, helped by the £7,500 Boiler Upgrade Scheme grant and a wave of lower-cost installers. An air source heat pump is no longer the exotic option: for most homes replacing a gas boiler this decade it’s the default question, and the answer turns on three things — install cost after grants, the quality of the installation, and your electricity tariff.

How it works: moving heat from outside air

An air source heat pump moves heat rather than making it. A fan draws outside air over a heat exchanger; a refrigerant absorbs that heat, is compressed to raise its temperature, and hands the heat to your radiators or underfloor loop and hot-water cylinder. Because the electricity only powers the moving and compressing, one kWh in yields roughly three to four kWh of heat out — an efficiency (SCOP) of 3.0–4.0 against a gas boiler’s ~0.90.

Two design differences from a boiler matter day-to-day. Heat pumps run at lower flow temperatures (35–50°C rather than 60–75°C), so they run longer and steadier, and some radiators may need to be one size larger. And they produce heat continuously rather than in bursts, which suits a well-insulated fabric — do the loft and cavity work first and the heat pump you need gets smaller and cheaper.

Air source heat pump cost in 2026

Air source heat pump grants in 2026

The Boiler Upgrade Scheme pays £7,500 toward an air source unit in England and Wales, runs to 2030, and goes through your MCS-certified installer — you never handle the money. Scotland offers Home Energy Scotland grants and loans on similar scale.

Once you understand how it works, the running-cost question becomes concrete. At a Q1 2026 price cap electricity rate of about 25p/kWh against gas at about 6.3p/kWh, the break-even seasonal efficiency is roughly 3.5 on standard tariffs. A good install beats that; heat-pump time-of-use tariffs (several suppliers now price overnight and smart-controlled units aggressively) put clear water between the pump and the boiler.

What installation involves

A proper air source heat pump installation starts with a room-by-room heat-loss survey — if a quote arrives without one, bin it. From there:

1. Design — unit sizing (typically 5–12kW for UK homes), flow temperature, radiator check, cylinder location. Insist on a design flow temperature of 50°C or lower; it’s the single best predictor of real-world efficiency.
2. The visible kit — the outside unit (roughly washing-machine sized, needs ~1m clearance), a hot-water cylinder indoors, and possibly a few radiator swaps.
3. The work — two to five days for a straightforward gas-boiler swap.
4. Paperwork — MCS certificate (required for the grant), DNO notification, and most units fall under permitted development in England, no planning application needed (listed buildings and some flats excepted).

Ask every installer for their design SCOP and for monitored performance data from past jobs. The gap between a 2.8 install and a 3.8 install is hundreds of pounds a year, forever.

Ground source and air-to-air alternatives

If you have land, a ground source heat pump trades higher install cost for higher efficiency; the same £7,500 grant applies. Air-to-air units (heating via fan coils, no radiators or hot water) are cheaper — often £2,000–£4,000 — but don’t qualify for the Boiler Upgrade Scheme and suit flats and single-room extensions better than whole houses.

For most gas-heated houses doing fabric-first improvements, the air source route through the grant is the mainstream answer — and at £3,000–£7,500 net it now competes directly with a premium boiler swap on capital cost, before the running-cost argument starts.

Frequently asked questions