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Minimum system volume

 
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Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 5417
11/08/2026 7:33 pm  

Posted by: @bobflux
↑

So far, mine hasn't defrosted yet, and the radiant ceiling was finished last month and isn't connected yet. I'll have to wait for next winter to see how defrosting feels... For the UFH loops I don't have any worries, the slabs are 10cm thick so there are tens of tons of concrete as thermal mass...

 

I don't notice mine defrosting, and most of the time Im in a room with a fancoil which is likely to be rapidly affected, and when its light I can see the clouds of vapour from the window.  There is negligible radiant effect from the fancoil so perhaps thats relevant.  I dont have a volumiser but I do have 200l system volume, way over the minimum.

What does happen is that the house cools at night when its minus numbers outside and its defrosting.  I expect that, the heat pump is more or less right size and I use quite mode overnight as a (probably unnecessary) courtesy to the neighbours so the resultant restriction on output means that recovery from defrost takes perhaps 20-30 mins so.  During the daytime it recovers very quickly from defrost because it ramps the compressor up to absolute maximum immediately after, but not when quiet mode is active.  Of course some people like the house to cool at night!

 


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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