Air source heat pumps (ASHP) and drainage - Why do heat pumps emit so much water?
Updated on 03/07/26 by Abby_OVO
As we’ve got plenty of Air-Source Heat Pump early adopters here, we’re hoping you might be able to share your experience of a little discussed aspects of your heating system: drainage.
Does your Heat Pump emit a lot of water?
Have you noticed your outside unit emitting water? If so, are there any factors that increase or decrease the amount of water released?
They do, from the humidity of the outside air. It condenses on the grille and drips off onto the ground or into a drip tray. That water has to be directed away to a drain. On a humid day it’s surprising just how much water runs off.
That’s what can freeze on the grille, which needs the defrost cycle to melt it off.
Depends on the size of unit and weather conditions. I've seen values of up to 10 litres per hour quoted. Potentially a problem if it just leaks across a path and starts to freeze as the condensate will keep building up in cold weather.
Or as of 3 days ago drips out the front left base of the heat pump as well ! Zero rainfall.
And how is the heat pump set up to deal with this?
There should be some drainage (in the same way that a condensing boiler needs a drain). Ours is piped to a nearby drain, although there was a puddle under it this morning so I wonder if the pipe isn't connected properly.
Ours had this drip tray to collect the water which then flows away into nearby drain:
Also check out the further comments below, or share your own experience with the community.😊
