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Multi-split AC sizing?

 
Air Source Heat Pumps (ASHPs)
Last Post by Clockworks 50 minutes ago
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 Clockworks
(@clockworks)
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Joined: 1 year ago
Posts: 59
Topic starter 17/07/2026 9:29 am   [#3105]

My 4 bed 1960's dormer bungalow has got a 6KW Mitsubishi Ecodan, which is more than capable of heating the house to 21 degrees on a zero degree day here in Cornwall.

Doing the maths on a zero degree day, our heatloss is actually around 4.5 KW, calculated on the actual energy consumed.

 

We are looking at getting a multi-split for cooling only, but worried that the suggested units are a bit too big, with a combined output of 8.5KW (2x 2.5 and 1x 3.5).

If it takes 4.5KW to maintain a delta of 21 degrees for heating, wouldn't it take 3KW to maintain a delta of 14 degrees for cooling (35 degrees down to 21 degrees)? Or, am I missing something?

The suggested units would seem to be oversized, and I'm concerned about cycling on all but the very hottest days. "Normal" summer days, we are looking at a cooling delta of 4 or 5 degrees.

Hottest OAT this year has been 33 degrees, but the upstairs room have got up to 35 degrees because of solar gain.



   
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