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Radiator sizing sanity check

Papahuhu · 2026-01-01T14:44:02Z

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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Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls

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Papahuhu

(@papahuhu)

Reputable Member Member

Joined: 12 months ago

Posts: 335

Topic starter 08/01/2026 1:40 pm

@jamespa

Luckily I have the whole process documented as I could see it had become a comedy of errors. The insulation measures were installed by a sub contractor to the sub contractor, neither of which were selected nor specified by myself nor have I ever signed off on any acceptance of work. I’m very comfortable I have the legal high ground, if it comes to that. I so hope it doesn’t, I don’t want the grief.

This post was modified 6 months ago by Papahuhu

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5174

08/01/2026 1:50 pm

Posted by: @papahuhu

↑

@jamespa

Luckily I have the whole process documented as I could see it had become a comedy of errors. The insulation measures were installed by a sub contractor to the sub contractor, neither of which were selected nor specified by myself nor have I ever signed off on any acceptance of work. I’m very comfortable I have the legal high ground, if it comes to that. I so hope it doesn’t, I don’t want the grief.

As I mentioned early on the cost of supplying and fitting a few rads is negligible. It certainly shouldn't come to legal proceedings if this is the bulk of whats needed!

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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