Heat pump for a flat: can you have one without an outdoor unit? What goes outside and what goes indoors
“Heat pump for flat” is searched 210 times a month in the UK and “indoor heat pump” 170; in Germany “Wärmepumpe Innenaufstellung” 2,900, in France “pompe à chaleur appartement” 1,600, in Italy “pompa di calore senza unità esterna” 1,900. People living in a flat want to know whether they can drop the gas boiler without putting anything outside. We answer with numbers: what is really needed, what goes outside, what goes indoors.
01
A heat pump takes its heat from the outdoor air
An air-to-water heat pump heats the home with the heat in the outdoor air, as we explain in the article on how it works. To do that it has to pass a lot of air over its coil: our Kita X moves 3,800 cubic metres an hour to deliver 7.5 kW. That air has to be taken from outside and sent back outside.
02
Without an outdoor unit: what it means
Units “without an outdoor unit” stand indoors and take air through holes in the wall: the air comes in through one hole and goes out through the other. Let us do the sum with the Kita X airflow: through a 20-centimetre hole the air would have to pass at 121 km/h, more than a hurricane on the Beaufort scale; with 40 centimetres at 30 km/h, with 60 at 13 km/h. That is why units with holes in the wall have little output, or need openings as big as a window. And with propane there is one more reason: the gas must stay outside the home.
03
Our solution: the unit outside, water indoors
For a flat we offer the Kita X, our 7.5 and 9 kW propane monobloc heat pump. It stands outside, on the balcony, terrace, garden or roof, and the spot is chosen with the installer following the rules for propane. Only two water pipes come indoors: the gas stays in the factory-sealed circuit. See the article on propane and the page on monobloc units.
04
Indoors: the cabinet instead of the boiler
Where the old boiler was, we put the built-in cabinet: 220 centimetres high, 95 wide and 40 deep, wall-mounted or semi-recessed. Inside is the whole plant room: the 134.5-litre hot water cylinder, the system buffer, the circulators, the 3-way valve, the dirt separator and the 7-inch touch panel, which can also be used remotely. For hot water see the page on hot water.
05
Noise on the balcony
The Kita X has a sound power of 53 dB(A). On a balcony, placement matters: away from the neighbours’ windows and without walls that bounce the sound back. Distances are in the article on noise, installation in the article on installation.
06
Radiators or underfloor heating
The unit works with underfloor heating and with radiators: ours reach 70 °C, but perform better with the water as cool as possible. How to tell whether your radiators are enough is in the article on radiators.
07
If you are looking at a hybrid
Many people in flats think of a hybrid system, gas boiler plus heat pump. That means two units, two maintenance plans and the gas contract that stays. To anyone looking at a hybrid we offer the Kita X, as we explain in the article on hybrids.
08
In a block of flats
If the building has central heating, a heat pump can serve the whole block: see the page on blocks of flats. If each flat has its own boiler, the Kita X replaces it flat by flat; for the unit on the balcony or facade, the building’s rules apply. The real limits of a heat pump are on the page on pros and cons. For an opinion on your flat, ask us for information.
09
Frequently asked questions
Is there a heat pump without an outdoor unit?
There are units that stand indoors and take air through holes in the wall, but they have little output: to deliver 7.5 kW the Kita X moves 3,800 m³ of air an hour, which through a 20 cm hole would travel at 121 km/h. To heat a flat you need a unit outside.
Can you put a heat pump in a flat?
Yes: the unit stands outside, on the balcony, terrace, garden or roof, and indoors the built-in cabinet with the cylinder and the whole plant room goes where the boiler was.
What heat pump do I need for a flat?
We offer the Kita X, a 7.5 and 9 kW propane monobloc with a sound power of 53 dB(A). The right output is calculated for the flat.
Where does the heat pump go in a flat?
Outside, where there is air: balcony, terrace, garden or roof, away from the neighbours’ windows and following the rules for propane. Only water pipes come indoors.
How much space is needed indoors?
The built-in cabinet is 220 cm high, 95 wide and 40 deep, and goes on the wall or semi-recessed where the old boiler was.
Does a heat pump in a flat work with radiators?
Yes: our units reach 70 °C, and they perform better the cooler the water that keeps the home warm.
All the technical tips are on the series page.
