Heating with an air conditioner (air-to-air heat pump): costs, limits and grants

Almost every split air conditioner can heat as well as cool. Technically it is an air-to-air heat pump: it takes heat from the outdoor air and blows it into the room through the indoor unit. With electricity much more expensive than gas per kWh, the question is whether that saves money. In mild weather it usually does; in hard frost the advantage mostly disappears. And in England and Wales there is a grant if you use it to replace your existing heating.

What does a kWh of heat cost?

To compare fairly, convert everything to the price of one kWh of heat in the room. We use the Ofgem price cap unit rates for 1 October to 31 December 2026 (GB average, Direct Debit) ¹:

• Electricity: 26.32p per kWh
• Gas: 7.97p per kWh

A modern condensing boiler turns roughly 90% of the gas energy into useful heat in practice.

At these prices the break-even point is an efficiency of about 3. Above that, the air conditioner heats more cheaply than gas; below it, gas is cheaper. A plug-in fan heater is by far the most expensive option.

Two caveats. As long as you stay connected to gas, you keep paying the gas standing charge – 29.68p a day under the cap ¹. And your own tariff may differ, especially on a fixed or time-of-use deal. Run the numbers with your own rates: electricity price ÷ SCOP versus gas price ÷ 0.9. Time-of-use electricity tariffs can shift the balance further towards the heat pump if you run it mostly in cheaper periods.

Where air conditioning works well – and where it doesn’t

Strengths:

• Fast heat – ideal for a home office, extension or loft that the central heating struggles to reach.
• Spring and autumn: above freezing, efficiency is high and the boiler can often stay off.
• Room-by-room control: you only heat the room you are in.
• The same unit cools in summer.

Weaknesses:

• No hot water. You still need the boiler or a cylinder for showers and washing up.
• Warm-air heating. Warm air rises; floors stay cooler than with radiators or underfloor heating, and some people dislike the airflow.
• Less output in frost. As it gets colder outside, the unit delivers less heat for more electricity, and the outdoor unit periodically defrosts.
• One indoor unit per room. Heating a whole house needs several indoor units or a multi-split.

Check SCOP and Pdesignh

The energy label gives the SCOP for the average European climate, with a design temperature of −10 °C, plus the design heating load (Pdesignh) ². If a room must stay warm through a cold week, Pdesignh should match the room’s heat loss; the nominal heating output in the brochure is measured in milder conditions and is higher. An A+++ unit (SCOP ≥ 5.10) uses over 20% less electricity for the same heat than an A+ unit with a SCOP of 4.0 ².

The Boiler Upgrade Scheme for air-to-air

The Boiler Upgrade Scheme offers £2,500 towards an air-to-air heat pump, compared with £7,500 for air-to-water or ground source systems ³. The main conditions ³:

• the property is in England or Wales;
• the installer is MCS-certified;
• the new system replaces existing fossil-fuel or electric heating, not an existing low-carbon system;
• air-to-air heat pumps are not eligible in non-domestic buildings, and new builds are excluded apart from some self-builds;
• the application must be made within 120 days of commissioning.

In practice, the installer applies for the grant and deducts it from your quote. Adding an air conditioner to a home that keeps its gas boiler as the main heating is unlikely to meet the “replaces” condition, so check with the installer before you sign.

In England, air-to-air heat pumps have also been covered by permitted development since May 2025, subject to the MCS 020(a) noise standard ⁴. More on that in our installation guide.

Air-to-air or air-to-water?

An air-to-air system makes most sense if you also want cooling and are heating a few rooms, or a small, well-insulated home. To replace a boiler across a whole house with radiators, air-to-water is usually the more natural step – see our heat pump grants guide and the heat pump overview.

Practical tips

• Point the louvres downwards when heating so warm air doesn’t pool under the ceiling.
• In the heating season, let the unit run steadily at a low setting rather than switching it on and off; inverters are most efficient at part load.
• Clean the filters regularly – clogged filters cost output and efficiency.
• If you plan to rely on the unit for heating, ask for a room-by-room heat loss calculation and compare it with Pdesignh.