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By electric, I don't mean ASHP, I mean water for UFH heated by electricity generated by PVs. I know you can get solar-powered UFH, I'm just struggling to visualise the system diagram for it. Where does the heating element go? In the buffer tank?
ffm-
Unless you live in a passivhaus, the space heating will be thirsty, and using direct electric resistance elements to do this will be wasteful as you could only ever approach 100% efficiency, or a ‘coefficient of performance’ of 1.
Using the same amount of leccy, whether from the mains or augmented by solar/battery etc to run a heat pump will achieve a much higher CoP, usually 3-4, meaning you get 3x the heat energy for a given input compared to direct resistance heating. So again, unless your house needs hardly any energy input to stay warm, you’d be mad to use anything other than a heat pump to heat your UFH.
ectoplasmosis
If by ‘electric’ you mean ASHP, then it’s exactly the same as a ‘system’ boiler, with a hot water tank, pump, buffer/volumiser as necessary, rads, wet UFH etc, with the only difference being that you have an outdoor monoblock heat pump unit heating the water being pumped instead of an indoor gas boiler. The only direct electric resistance ‘element’ in the system might be a backup immersion heater for the hot water cylinder, but this isn’t essential.
The flow temperatures should ideally be lower with ASHP, therefore any rads should be larger.
As for the EPC requirement, you can check if your house has one on the gov.uk website, most do. If it doesn’t, obtaining one isn’t hard or expensive.