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We’re currently claiming the full £7.5K BUS grant for installing ASHP as part of an ongoing refurb/extension; just find a friendly independent MCS-certified installer and it’s not a problem.
Solar on its own for heating won’t work (unless you have a field you can cover with PV panels). Most efficient system is solar PV charging a battery and running ASHP to ‘charge’ a thick, well-insulated UFH slab during off-peak periods of a smart energy tariff, then running your house from the battery and exporting solar at a high rate during the day.
Initial outlay for such a setup is very high, and payback often long enough to make it not worthwhile if your only criteria is reducing energy bills.
Sack off the gas if you can afford to.
ectoplasmosis-
That's really interesting. This bit confused me as to how you're meant to apply if you're getting a whole house refurbed including insulation and an ASHP in place of a gas boiler:
"Your property must have a valid Energy Performance Certificate (EPC) with no outstanding recommendations for loft or cavity wall insulation."
https://www.gov.uk/apply-boiler-upgrade-scheme/check-if-youre-eligible
...but you're still applying for the grant despite getting everything done at once?
I'm not thinking that PV would heat the house under all circumstances. I think we'd have to rely on a combi boiler a bit, but we could substantially reduce our use of it from the PVs. What I'm struggling to understand is what an electric wet-UFH system looks like. Where does the element go? Is there a buffer tank and an expansion vessel? How big are they?
ffm
Having written off an ASHP for our imminent total house refurb/extension we've been discussing it again in light of reports of prices dropping. It's still not clear whether we can get a grant for it as part of a complete thermal upgrade of the house or whether you would have to delay the installation of it until after all the insulation, windows etc. are done in order to apply for the grant.
If it doesn't turn out to be feasible (either due to a lack of a grant or it not being possible to put the external unit anywhere sensible) one other option that might be worth considering is a solar panels driving wet under-floor heating (since our roof is bang-on south-facing), with a gas boiler backup. I've read that such systems exist, but I've not found a schematic of them. Is there a separate expansion tank for the ufh loop with an element in it?