Yes, many wall-mounted air conditioners can heat as well as cool. In heating mode, a reversible split system brings heat from outside into your room. It can be economical for one room, but heating a whole home takes a system designed for every room you need to warm.
Whether it saves money depends on what you use now, your energy prices and how efficiently the system works in your home.
How does an air conditioner heat a room?
A reversible split air conditioner is an air-to-air heat pump. In summer, it moves heat out of your room. In winter, it reverses direction and transfers heat from outdoor air indoors. The indoor unit then blows warm air into the room. Energy Saving Trust explains how air-to-air systems work.
Because it moves heat rather than producing it all from electricity, it can deliver several units of heat for each unit of electricity it uses. Check the specifications for heating mode and capacity; some appliances only cool.
These systems usually recirculate indoor air, so you still need ventilation.
How much does AC heating cost compared with gas and electric heaters?
To compare heating fairly, look at the cost of heat delivered, not just the price of electricity and gas. The table uses Ofgem’s average Great Britain unit rates for October to December 2026: 26.32p/kWh for electricity and 7.97p/kWh for gas, for a standard variable tariff paid by Direct Debit.
| Heating method | Assumed efficiency | Cost per kWh of heat |
|---|---|---|
| Plug-in electric heater | 1 unit of heat per unit of electricity | 26.32p |
| Reversible AC | 2.5 units of heat per unit of electricity | 10.53p |
| Reversible AC | 3 units of heat per unit of electricity | 8.77p |
| Reversible AC | 3.5 units of heat per unit of electricity | 7.52p |
| Gas boiler | Illustrative 90% efficiency | 8.86p |
In the middle AC scenario, 3 kWh of heat costs about 26p, compared with about 27p from the example gas boiler or 79p from a plug-in heater. These are calculated examples, not measured home costs.
The AC scenarios are not guaranteed seasonal averages. The table excludes standing charges, equipment, installation, hot water and servicing. Northern Ireland has a separate electricity market; check your Consumer Council tariff comparison and gas bill instead of using Great Britain averages.
Will it heat an entire home?
A single wall unit can heat the room it serves, or a genuinely open area. It will not reliably heat several closed bedrooms through doorways and around corners. For a whole-home system, an installer needs to calculate each room’s heat loss and design enough indoor units, or another suitable way to distribute heat.
Insulation, draughts and layout affect comfort and cost. Energy Saving Trust notes that these systems can suit smaller homes and flats, but the right design depends on the property.
If you keep central heating, a split can heat one occupied room. Savings depend on how you use both systems.
Does it work in cold UK weather?
A suitable heat pump can still extract heat from cold outdoor air. However, its heating output and efficiency can change as temperatures fall. Frost may also make the outdoor unit pause to defrost. Do not assume a figure measured in mild conditions will apply throughout a winter.
Ask the installer how much heat the proposed system delivers on a cold day in your area and whether it can cover each room’s calculated heat loss. Energy Saving Trust’s installer guidance stresses checking manufacturer performance at the chosen outdoor design temperature.
What happens to hot water?
Most wall-mounted air-to-air systems do not heat water for taps, showers or baths. If you keep your gas boiler for hot water, include that continuing gas use and standing charge when comparing bills. If you plan to remove the boiler, price a separate hot-water solution as part of the project.
Some specialist systems can supply hot water, so check the specific model. Energy Saving Trust sets out the available options.
Can you get a grant for heating with AC?
The Boiler Upgrade Scheme currently offers £2,500 towards an eligible air-to-air heat pump in England and Wales. This applies to replacing an existing heating system, not simply adding a bedroom AC unit while keeping your current heating.
Ofgem’s rules require an installer certified by the Microgeneration Certification Scheme (MCS) and a new system sized to meet the property’s full space-heating needs. The property’s heating and hot-water requirements must be covered. Ask an eligible installer to confirm the complete design and grant conditions before counting on the discount. The Boiler Upgrade Scheme applies in England and Wales.
Our planning-permission guide covers the separate approvals for an outdoor unit.
When could it make financial sense?
AC heating is especially worth considering if you currently heat a frequently used room with a plug-in electric heater. If you already have a reversible split, try its heating mode and compare your electricity use with your previous heating pattern.
The decision is less obvious when comparing to a gas boiler. At the rates in our table, an AC system delivering around three units of heat per unit of electricity is roughly on par with our 90%-efficient boiler in energy cost per unit of heat. Better or worse real performance changes the result. If you keep gas for hot water, the gas standing charge remains; if you disconnect it entirely, your comparison changes.
Weigh the cost of buying and fitting units against any savings.
For the upfront side of the decision, read our UK installation-cost guide.
Estimate costs for your home
Note your current heating fuel, tariff, rooms, daily heating hours and hot-water arrangements. Then ask installers for a room-by-room design and a realistic winter efficiency estimate. Compare the complete heating plan, not one attractive hourly figure.
CostToCool’s free Calculate my current setup and Plan cooling for my home tools estimate cooling costs and capacity. They don’t currently calculate winter heating costs, so don’t use their results as a heating quote. For that, use the proposed system’s heating specifications, your tariff and an installer’s assessment.