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Help me keep the faith with my air source heat pump installation

 
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Air Source Heat Pumps (ASHPs)
Last Post by Toodles 3 days ago
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2334
13/04/2025 12:19 pm  

Posted by: @adamk
↑

Also I’m not entirely convinced the heat loss the last company did is that accurate 

I apologise if this has been covered already but have you got any way to sense check loss calculations eg from past usage.  The two, three hour full professional surveys I had done on my house both said 16kW, the actual loss is 7kW.  This may be extreme but illustrates how far out surveys can be 

This post was modified 4 days ago by JamesPa

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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 AdamK
(@adamk)
Estimable Member Member
Joined: 2 months ago
Posts: 65
Topic starter 13/04/2025 6:51 pm  

@jamespa I’ve had a few done most come out around 7kw so that’s probably about right, but the loss per room I’ve only got one and it’s been corrected a few times but one bedroom is still listed 2m2 smaller than it is.


   
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 AgentGeorge
(@agentgeorge)
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Joined: 2 months ago
Posts: 11
13/04/2025 7:29 pm  

@jamespa to be that far out the assessor has got the insulation thickness of the floor, walls and ceiling too thin.

i have 150mm thickness but its celotex not rockwool, took ages to explain that to the assessor who could only input thickness and not the true R rating.


   
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 JamesPa
(@jamespa)
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14/04/2025 7:53 am  

@adamk Sounds encouraging, what about any independent measure of total loss eg from current gas/oil consumption.

Rooms share heat to a fair extent so it's debatable how much precise room by room losses matter, so long as they are roughly right.  If in doubt oversize emitters and turn down the lsv (or flow temp if they are all oversized).  Much more important to get the total right so your heat pump is right-sized.

 

Posted by: @agentgeorge
↑

to be that far out (16 kW Vs 7kW actual) the assessor has got the insulation thickness of the floor, walls and ceiling too thin.

I got the calculation details for one of the two surveys, they ignored any fabric upgrades they couldn't see (principally insulation for the solid walls) even though I made a big point of telling the surveyor about them, double counted room to room losses and overestimated ventilation loss.  I presume the other surveyor must have done similar.  GIGO

This post was modified 3 days ago 2 times by JamesPa

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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 AdamK
(@adamk)
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Joined: 2 months ago
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Topic starter 14/04/2025 3:08 pm  

@jamespa what I didn’t want to do was oversize too much then end up having the HP cycling. What I have noticed is most companies I’ve contacted want to fit a 45L Vaillant buffer/volumizer? Yet after watching this weeks QA vid a guy on there said no buffers.


   
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 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 2 years ago
Posts: 2334
14/04/2025 3:33 pm  

Posted by: @adamk
↑

@jamespa what I didn’t want to do was oversize too much then end up having the HP cycling. What I have noticed is most companies I’ve contacted want to fit a 45L Vaillant buffer/volumizer? Yet after watching this weeks QA vid a guy on there said no buffers.

The guy was right as regards buffer tanks, avoid.  However a 2 port volumiser is ok. Unfortunately terminology isn't quite consistent.

Check that it's got 2 ports only.  2 ports good, 3 or 4 ports bad.

 

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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Toodles
 Toodles
(@toodles)
Famed Member Contributor
Joined: 3 years ago
Posts: 1900
14/04/2025 3:47 pm  

@jamespa “They are all equal but, some are more equal than others.” 😉

Toodles, he heats his home with cold draughts and cooks his food with magnets.


   
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