Building’s Forum has a special discussion group for sustainability. This week, a member asks a question about where to install an air-source heat pump.

Q: Can an air souce heat pump be fitted in a loft?

Hi, I want to fit a 12kw air source heat pump into a loft space. I have read claims by quite a few suppliers that this is not a problem but also seen a couple of posts that this is totally the wrong thing to do.

Their arguments for it not being OK are:

  • The noise (I’m not too concerned by this)
  • Because of the way the air source heat pump works, it will give out cold air and this will rapidly cool the loft space, making the pump inefficient.

The loft space is large (50ft x 40ft x 10ft) and well ventilated. Can anyone advise if it is OK to fit the pump in a loft or not? Thanks.


A: I would only recommend the 3 and 5KW air source heat pumps in loft spaces.

But if your loft space is very large then I can see no reason for any problem with the 12KW - just remember to bulk up the area it is going to sit in structurally, allow enough area to get it up and in there and also situate it within an area that is not above any bedrooms.

Heat rises and you are recycling the heat already created from whatever the heat source is in your house, underfloor or radiators. The cold air will cool the loft but you could always channel this away through adequate ventilation.


A: Heat pump efficiency - because of the voltage drop, mains electricity is only 30% efficient, therefore a 300% output heat pump (that is, 3kW heat from 1kW electricity) is about as environmentally friendly as an efficient mains gas boiler and is also much, much more expensive to install.

Remember that efficiencies quoted by manufacturers will be theoretical peak values and actual performance is likely to be considerably lower for much of the working life of the air source heat pump.

Heat pumps only “work” environmentally if there is no mains gas, so unless you’re off grid, just have a good boiler fitted. If in any doubt check out Barry’s post about exhaust air heat pumps.