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"Condensing" heat pumps?

Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 5 months ago

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madbilly

(@madbilly)

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Topic starter 23/06/2025 2:42 pm

Hi everyone,

I just need a sanity check please. I've heard/read (IIRC) a few times recently people talking about "condensing" heat pumps, like condensing boilers. Now, I know that ASHPs have condensors, they condense the water vapour out of the air and release the latent heat of evaporation in it, which is then transferred to the water (if I've understood correctly). But, is there something else specifically called a "condensing heat pump"? If not, and what I understand to be a normal ASHP is the only real condensing heat pump, then is there such a thing as a non-condensing ASHP?

Cheers 🙂

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Majordennisbloodnok

(@majordennisbloodnok)

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23/06/2025 3:20 pm

I'm certainly not an expert and therefore not best placed to give a definitive answer, but I've never personally heard of a condensing heat pump in the sense of a home-heating unit. As you say, a heat pump will contain a condenser and may produce condensate as a byproduct of the way it works, but that's not what you're asking.

One thing that might be worth mentioning, though, is that an air source heat pump is not trying to release the heat from the moisture content in the air; merely heat from the air in its entirety. As other threads on this forum have mentioned before, a heat pump will actually work at its most efficient when dealing with dry air, hence why they can work with surprisingly good efficiency in very cold countries like the Nordics.

In contrast, heat pumps do also exist in condensing tumble driers and in that situation condensation is precisely what they want to achieve, whilst at the same time recirculating the recovered heat back into the drum to maximise energy efficiency. If I were pushed to suggest (and it's only a guess) what someone might mean by "condensing heat pump", I'd point somewhere like there and guess it might be to describe a heat pump where the focus is on water removal rather than heat transfer. All in the context.

I may, of course, be talking complete rubbish. I have done so plenty of times in the past and I'm sure I'll continue for some time to come.

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JamesPa

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23/06/2025 4:12 pm

Same here as above. Where have you seen this terminology?

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Judith

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23/06/2025 7:32 pm

Never heard of them, but might just be my ignorance. They need a drain because when de-icing the melted ice has to go somewhere.

Please capture the web page etc when you next see the mention and we can all learn something!

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Mars

(@editor)

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23/06/2025 8:00 pm

Good question and you’re not wrong to question the term.

Strictly speaking all heat pumps are condensing in the sense that they rely on refrigerant condensing and evaporating. But calling a heat pump condensing is a bit like calling an oven a “heating oven”… technically true, but totally redundant.

It’s likely people are mixing up boiler terminology, where condensing refers to recovering extra heat from combustion gases. That doesn’t apply to heat pumps.

So I don’t think there’s such thing as a non-condensing heat pump if it’s functioning properly. It’s just a case of crossed wires in terminology from what I think.

I am, however, at Installer tomorrow and Wednesday so will ask the real experts in the field to double check.

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Scalextrix

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24/06/2025 6:29 am

There are heat recovery heat pumps that are designed to work on exhaust gasses from other processes, in an industrial setting for example. They could cause condensation in the exhaust gas...

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madbilly

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Topic starter 24/06/2025 8:49 pm

Hi everyone,

Thanks for clarifying my misunderstanding about the role of the condenser and that heat pumps actually work better with dry air not humid air. That's where I'd got mixed up with condensing boiler when trying to wrap my head around what a "condensing heat pump" might be.

The context was space heating, not clothes drying, which rules out the tumble drier (unless they'd got confused about that).

I can't find where I read it online now, so maybe I didn't. I overheard it in a conversation at work where two people were definitely talking about space heating.

Yes an exhaust heat recover heat pump could be what they were referring to, although that's not relevant for most houses.

If I get to the bottom of it I'll post back here 🙂

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JamesPa

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24/06/2025 8:59 pm

Posted by: @madbilly

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Yes an exhaust heat recover heat pump could be what they were referring to, although that's not relevant for most houses.

There are DHW tanks with a built in heat pump that take their intake from the house, the outside world or the loft. Sometimes these are described as exhaust heat recovery although thats a bit of a misnomer.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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