Heating with air conditioning
A reversible split system is an air-to-air heat pump. It heats fast, room by room, at an efficiency no combustion can match.
Why 1 kWh of electricity becomes 4 kWh of heat
A heat pump does not create heat, it moves it. Even cold outside air holds energy, which the refrigerant absorbs at low pressure. The compressor raises the pressure and therefore the temperature, and the indoor unit releases that heat into the room. Electricity only drives the transport, which is why one kilowatt-hour delivers three to five times as much heat depending on the outdoor temperature.
The seasonal figure for this is SCOP. A unit with a SCOP of 4.6 delivers an average of 4.6 kilowatt-hours of heat per kilowatt-hour of electricity across the season. For comparison, a condensing gas boiler manages around 0.95 to 1.05.
What that costs in winter
Example for a 30 m² room with a heat demand of about 2,000 kWh per heating season. Energy prices are assumptions – check your own tariff.
| Heat source | Efficiency | Energy needed | Cost per season |
|---|---|---|---|
| Air conditioner (SCOP 4.5) | 450 % | 444 kWh electricity | approx. €90–130 |
| Gas boiler | 98 % | 2,040 kWh gas | approx. €160–220 |
| Direct electric heating | 100 % | 2,000 kWh electricity | approx. €400–580 |
With your own solar PV the comparison shifts further in favour of the heat pump, because part of the electricity costs nothing.
Where the limits are
An air-to-air heat pump heats air, not water. It replaces neither underfloor heating nor hot water production. In an older building with high heat demand it rarely replaces central heating entirely, but it takes a great deal of load off it, especially in spring and autumn when a boiler runs badly at part load.
It makes most sense where electric heating was used before, in extensions and attic rooms without radiators, in home offices and in well-insulated new builds.
- Very economical in the shoulder seasons
- Heats room by room rather than the whole house
- No water circuit, no domestic hot water
- In hard frost output drops and defrost cycles kick in
Subsidies in Luxembourg
Luxembourg supports energy work on residential buildings through the Klimabonus programme, which focuses primarily on heat pumps as a heating system, on insulation and on renewable energy. Whether an air-to-air system qualifies in a given case depends on how it is installed and what role it plays in the heating system.
In addition, the reduced VAT rate for housing may apply to work on a main residence. Both need to be clarified and applied for before the order is placed. During the consultation we tell you what is realistic for your project and point you to the competent authorities for the binding answer.
Questions about heating mode
Does it work below freezing?
Yes. Current units heat down to roughly −15 to −20 °C outside. Output falls as it gets colder, so heating design should use the figure at −7 °C rather than the nominal rating.
Does the outdoor unit ice up?
In damp, frosty weather frost forms on the heat exchanger. The system then briefly switches to defrost mode and meltwater drips off. A drain or heated tray stops ice forming on the path below.
Does it dry out the air?
In heating mode the unit removes no moisture from the room air, unlike in cooling mode. If the air feels dry in winter, that comes from cold outside air entering when you ventilate, not from the unit.
Can I get rid of my gas boiler?
In a well-insulated open-plan house that is possible if hot water is solved separately. In most existing buildings hybrid operation makes more sense: air conditioning in the shoulder season, boiler in hard frost.
Find out whether heating mode pays off
Tell us the year of construction, the floor area and your current heating. You get an honest assessment, including when switching is not worth it.