Air to Air Heat Pump: What the £2,500 Grant Pays For, and What It Doesn't

An air to air heat pump moves warmth from outside air into the room, using a refrigerant that runs between an outdoor unit and the indoor units. There is no water in the loop, which is why it needs no radiators.

The indoor unit is usually fixed high on a wall, close to the outdoor unit, and the refrigerant pipes often run in a slim plastic channel along the top of the wall. One outdoor unit can serve more than one indoor unit, but each extra room means more pipework. Many models can run in reverse in summer and cool the room.

The Department for Energy Security and Net Zero (DESNZ) published modelling in July 2026 on how reversible air to air heat pumps behave in UK homes. Two findings stand out:

• Heat per unit of energy: with small electric heaters added in rooms such as bathrooms, the systems delivered roughly 2.5 to 4 units of heat for each unit of electricity. Air to water heat pumps typically managed 3 to 3.5, and a combi gas boiler about 0.9 per unit of gas.
• Cooling: a modelled living room with cooling switched on went above 25°C for no more than 15% of the cooling season.

The report is clear that its air to air numbers are less certain than the figures for other systems, because they come from a small amount of data.

A home qualifies when the owner is replacing an existing fossil fuel or electric heating system and the new system can heat the whole property. Ofgem's installer guidance lists the points that most often trip people up.

• It has to replace what you have. The old system must be gas, oil, LPG, coal or electric heating that is not a heat pump. Storage heaters, electric panel radiators and electric boilers all count.
• It has to cover the whole home. The system needs enough capacity to meet 100% of the property's space heating needs, so one small unit in a larger house is unlikely to do. Two or more air to air heat pumps can count together, and one grant covers the lot.
• The main unit must be new. The heat-generating unit, compressor included, cannot be second-hand or kept from an earlier system.
• Exhaust air to air units are out for now. Ofgem says they cannot currently be certified under MCS.
• Some homes are excluded. GOV.UK rules out most new builds, social housing, and homes that have already received government funding for a heat pump or biomass boiler.
• No double funding. A heat pump that has also been promoted as an ECO measure rules the property out.

Most air to air heat pumps heat the air, not your taps, so hot water has to come from somewhere else. Ofgem's guidance says the heat pump, together with any permitted supplementary appliances, must be able to meet the property's space heating and hot water demand.

If a gas combi boiler makes your hot water today, the scheme expects that old fossil fuel system to be replaced, so the water heating needs a plan before you commit.

Common answers are an electric immersion heater in a hot water cylinder, which the guidance lets you keep if it is in good condition, or a hot water heat pump alongside. The Energy Saving Trust also lists electric showers with point of use heaters, and models that heat a cylinder directly, though few exist so far.

DESNZ's modelling shows why this matters for running costs. In most of its scenarios the hot water came from an immersion-heated tank, and the overall bill often came out higher than with other systems.

One exception stood out. A studio flat with an air to air system and an integrated 120 litre tank had the lowest annual cost of any option modelled, a gas boiler included. The report notes that systems linked to larger 230 litre tanks are planned.

The Energy Saving Trust puts typical costs at about £1,900 for one room and about £3,700 for a three-bedroom semi-detached house, before any grant. Its figures were checked on 6 November 2026, and extras such as redecorating can add to them.

The grant needs a system able to heat the whole home, so the one-room figure is a floor, not a guide to a qualifying system.

For the loan side, GOV.UK's Warm Homes Loan factsheet of 27 October 2026 lists a cap of up to £10,000 for an air to air heat pump, with the note "when MCS certification available". Our heat pump finance page explains how loans and grants fit together. For air to water pricing, see the air source heat pump cost page.

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