rad size and efficiency - Air Source Heat Pumps (ASHPs)

RE: rad size and efficiency

JamesPa — Fri, 28 Feb 2025 16:08:33 +0000

what if i set the system so its controlling on flow temp only, surely it would then just be a case of seeing which rooms dont get to 20c and upgrade those?

Adia Thermal sort of advocate this approach and produce some hardware to aid the determination.

In many cases however it will be obvious that an upgrade is needed, best in my view to do the calculations up front. If any are marginal then you could adopt the suck it and see approach for those. You need an increase in area of a factor of 2 or more if you move from a system designed for a boiler at a flow temp of 70C to a system designed for a heat pump at 45C, but if you have added insulation since the original installation, or the rads were anyway oversized, some may be reusable (some of mine were)

RE: rad size and efficiency

BU — Fri, 28 Feb 2025 11:19:47 +0000

@adamk Yes you can to that. I never use old radiators. If the customer insiste, I walk away, it is not worth it.

RE: rad size and efficiency

AdamK — Fri, 28 Feb 2025 11:00:28 +0000

@heacol

what if i set the system so its controlling on flow temp only, surely it would then just be a case of seeing which rooms dont get to 20c and upgrade those?

RE: rad size and efficiency

BU — Fri, 28 Feb 2025 10:40:37 +0000

It is just thermodynamics, the higher you move the flow temperature the more it will cost to run, existing radiators may need a higher flow temperature so the heat pump will cost more to run, your radiator upgrade, will usually be paid for in less than 2 heating seasons.

rad size and efficiency

AdamK — Fri, 28 Feb 2025 10:19:02 +0000

im going to have a Vaillant fitted and just see how it runs with the rads i have currently. how does having potentially undersized rads affect efficiency? or does it only affect comfort? assuming im controlling on weather comp?