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Air Source Heat Pumps (ASHPs)
Last Post by Mikeatthezoo 3 hours ago
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 Mikeatthezoo
(@mikeatthezoo)
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Topic starter 25/09/2025 12:37 pm  

First up, I apologise in advance.  I have tried to consume a vast amount of information, some of it I understand, some of it I do not, but all of it I believe forms part of a puzzle I’m trying to solve.

I am looking at getting a heat pump installed, replacing a 15kw gas boiler and 150L UVC that sits in the region of 65 degrees with a pump, size to be determined, with a cylinder I believe needs to be 250L+ (4 bed, 3-5 occupants).

First problem, easily answered - space heating.  We’ve had a few estimates, all either side of 5kw.  That - for the brands we’re looking at (Vaillant, Daikin and Mitsubishi) - is an easy answer; the Vaillant 7kw, and the Daikin and Mitsubishi 6kw.

The concern I have is keeping that cylinder warm during use.  Whilst we’re not hot washing cars and running five baths at once, I am worried that as we drop cylinder temperature to 50 or even 45 ideally we will start to become more dependent on heating water quickly after it is used.  6kw doesn’t go very far in that context.

Looking at all of the information, it appears that the Daikin and Mitsubishi 8kw (not the 8.5) are physically very similar to the 6kw and as a result from a modulation standpoint make no difference in the mild seasons, but provide substantial benefit for DHW.  Is this correct?

If it is correct, where is the 8kw Mitsubishi R290 going?  It seems to be on it’s way out having survived a whole year before they introduced the 8.5kw, which as far as I can tell is a bigger starting point resulting in higher lowest output numbers?

Sorry for all this.  My brain is absolutely addled trying to understand all of this and I’m faced with a very long term decision with sales speak pulling me multiple directions.



   
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