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Radiator sizing sanity check

 
Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by Papahuhu 2 hours ago
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 Papahuhu
(@papahuhu)
Estimable Member Member
Joined: 5 months ago
Posts: 46
Topic starter 01/01/2026 2:44 pm  

Hello

Looking for a sanity check please.

We recently (back in July) had a heat pump install, moving from a condensing gas boiler. They did all the usual MCS things before the install. 
One thing they proposed was to increase the size of all all my downstairs rads by approx 50% output and decrease the size of all my upstairs radiators by 50%. All of the 20+ rads were changed out.
Previously the house had been relatively warm and uniform throughout. Following the install, the downstairs rooms remain warm and the upstairs rooms are freezing, running between 5-7C below design temperature. 

At the time of the install I very heavily challenged what they were doing, as to me it’s common sense that in moving from deltaT50 to deltaT30, halving the radiator size effective reduces the heat output by 75%. But they insisted that this is what their heat loss survey indicated. We had added approximately 200mm of loft insulation, bring it up to the 300mm standard, but surely that alone won’t reduce the heat requirement by 75%. 

They have now agreed to repeat the heat loss survey using a revised methodology. Am I best to allow them to continue this or should I, in parallel, contact MCS and get them to initiate an investigation via their professional certification body. The installer has been a little slow but did act when I collected my own data using remote sensing devices in several rooms. My instinct tells me to give the installer room to remediate before starting a formal complaint, or am I being naive please?

thanks



   
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