When the unit is reversible, a ductless heat pump and a split air conditioner are the same hardware family: outdoor unit, indoor unit, refrigerant pipes, no house ducts. The heat pump adds a reversing valve and a heating rating so it warms the room as well as cooling it. Most UK domestic wall splits sold now are that heat pump. A cooling-only model looks similar and simply lacks proper heating. Energy Saving Trust treats the reversible units as air-to-air heat pumps.
The same boxes, with a reversing valve
In cooling, the indoor coil absorbs heat and the outdoor coil dumps it. In heating, the cycle reverses. The box on the wall does not change into a different appliance. What changes is whether the model is built and rated to heat at the outdoor temperatures you care about.
American pages say ductless heat pump versus ductless air conditioner. UK pages say reverse-cycle split versus cooling-only. Ask which you are being quoted. If you want the living room warm on a cold evening without running the whole boiler, you want the heat pump version and its SCOP, not a cooling-only chassis. Reversible means heating and cooling from the same indoor. Both need 230 V UK equipment, not a 115 V import.
Heating tables, cooling-only rooms, and the boiler
Cooling capacity in kW, heating capacity at a stated outdoor temperature, SEER, SCOP and sound should all be on the sheet. A unit that cools at 3.5 kW may not deliver 3.5 kW of heat at freezing point. If the room has no radiator and this unit is the only heat, that table is the design, not a footnote. Heating output falls as the outdoor air gets colder. The UK energy label covers the declared seasons. Compare two UK model codes on the same test.
Some commercial rooms and server spaces only need heat removal. A house almost always benefits from heating, because the install cost of the pipes and outdoor unit is already spent. The extra for a reverse-cycle indoor is small beside a second winter of electric heaters. Cooling-only is still a split, with the same F-gas install.
A heat pump split does not automatically replace a boiler, hot water, or heating in rooms without an indoor unit. It conditions the rooms where the indoors are fitted. Energy Saving Trust explains that role in plain terms for air-to-air units. Tell the installer you want heating as well as cooling, and ask them to write the heating capacity they are relying on. If the quote is silent, you may have been offered cooling-only by habit.
Pipes, power, condensate and a legal outdoor spot
F-gas certification for the refrigerant work, a safe electrical supply, a condensate route, and a legal outdoor position apply to both versions. In England, Planning Portal conditions cover many air source heat pumps on houses. Flats and listed buildings need their own consent checks.
Frequently asked questions
Is a UK split air conditioner a heat pump?
The reversible models are air-to-air heat pumps. They heat and cool. Cooling-only models are the exception and should be labelled as such on the quote.
Do I need a separate heater and a separate cooler?
Not for the rooms served by a reverse-cycle indoor. One system does both. Rooms without an indoor unit still need their own heat.
Does heating mode use the same outdoor unit?
Yes. The same outdoor and indoor pair reverse the cycle. The outdoor unit must still be sited for airflow, noise and service in both seasons.
Do US SEER2 numbers replace the UK label here?
No. The UK energy label covers the declared seasons. US SEER2 numbers do not replace it. Compare two UK model codes on the same test.
Core buying guides
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Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.