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Sizing of heat pumps

 
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Air Source Heat Pumps (ASHPs)
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Mars
 Mars
(@editor)
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Topic starter 21/04/2021 10:11 pm  

@bobbt9866, so do Freedom make their own ASHPs? I was not aware of that if they do. 

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 batalto
(@batalto)
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21/04/2021 10:40 pm  

@editor no they are just a supplier of them. Mine is coming from them, via an installer

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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 bobbt9866
(@bobbt9866)
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Posts: 46
22/04/2021 10:10 am  

@editor

Freedom are a distributer of Heat Pumps but also add a bit more added value to their support services


   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 4 years ago
Posts: 3242
Topic starter 24/05/2025 11:00 am  

We’ve published a deep dive into heat pump sizing, and we’d love to hear from you. Did your system turn out to be the right size? Does it keep your home warm when temperatures drop?

There’s a quick poll at the end of the article... please take a moment to vote and share your experience:

https://renewableheatinghub.co.uk/the-heat-pump-sizing-mess-why-are-we-still-getting-this-so-spectacularly-wrong/

Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb

Subscribe and follow our Homeowners’ Q&A heat pump podcast


   
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 benson
(@benson)
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Posts: 106
31/05/2025 11:48 am  

We have a Clivet 6.1 (12 kW). The datasheet provides output figures for OAT of 7, 2 and -7, at set water temperatures.

Is there somewhere where we can find the heating output at specific design temp (-2)/flow temps, or is it a case of querying with the manufacturers? Just wondering how installers decide the right capacity when it isn't overly clear from what I can see, even from the datasheets.


   
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 Old_Scientist
(@old_scientist)
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Posts: 162
31/05/2025 1:59 pm  

Posted by: @benson
↑

We have a Clivet 6.1 (12 kW). The datasheet provides output figures for OAT of 7, 2 and -7, at set water temperatures.

Is there somewhere where we can find the heating output at specific design temp (-2)/flow temps, or is it a case of querying with the manufacturers? Just wondering how installers decide the right capacity when it isn't overly clear from what I can see, even from the datasheets.

I agree it's not very helpful. Generally, the max heat output at -2C is going to be a little lower (maybe 3-5%) that the figure at -7C. That may sound counter-intuitive, but it's because of the likelihood of defrost cycles occurring at -2C, whereas the air is 'dryer' (less moisture) at -7C so less likely to encounter frosting / defrost cycles which reduce the overall amount of available heat. Anyway, the figures for 2C, -2C and -7C are not going to be a million miles apart, and if they are very close to your heat loss then you probably want to go for a larger heat pump. Most heat loss surveys are going to contain far larger variances (or errors) than the variances between manufacturers output data at 2C, -2C and -7C OATs

 

 

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 3.645kWp solar (south facing), Fox ESS inverter.
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.


   
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