jayc89 Posted February 1, 2022 Share Posted February 1, 2022 We currently have approx. 65sqm of UFH pipe run at 150mm centres that we run at 40c quite comfortably and are currently planning an extension which would bring the overall floorspace to 165sqm, or 1,100m of UFH pipe at 150mm centres. It's currently heated by our system boiler. The current slab is 60mm Cemfloor screed on top of 100mm PIR, but for the extension we plan on 200mm EPS and a 100mm floating reinforced concrete slab. Given our UFH can manage at 40c, I was wondering whether we should consider an ASHP as part of our extension just to heat the UFH loops. is 40c still too hot to realise any cost savings from an ASHP? Would we get a single ASHP, that doesn't cost a fortune, large enough to heat the approx. 132l of water flowing through these loops? Link to comment Share on other sites More sharing options...
ProDave Posted February 1, 2022 Share Posted February 1, 2022 An ASHP will do 40 degree UFH water comfortably. You size the ASHP based on the heat loss from the building. Your present gas / oil usage should give you an idea, if you can measure the usage on the coldest day in winter. Link to comment Share on other sites More sharing options...
J1mbo Posted February 1, 2022 Share Posted February 1, 2022 The circulating volume needs to be enough to avoid short cycling and 132 litres may well be not enough. Link to comment Share on other sites More sharing options...
Kevm Posted February 1, 2022 Share Posted February 1, 2022 How is your house heated now? It sounds like an ASHP may work for you but it's unlikely to be cheaper than gas at current prices. Oil maybe, LPG probably. Link to comment Share on other sites More sharing options...
jayc89 Posted February 1, 2022 Author Share Posted February 1, 2022 34 minutes ago, J1mbo said: The circulating volume needs to be enough to avoid short cycling and 132 litres may well be not enough. How would that be calculated? 3 minutes ago, Kevm said: How is your house heated now? It sounds like an ASHP may work for you but it's unlikely to be cheaper than gas at current prices. Oil maybe, LPG probably. Gas system boiler, it's a 32kw Baxi Platinum. This is my concern. I think an ASHP would work but I don't know whether the COP at 40c would be enough to realise any savings over sticking with gas. I'd prefer to reduce our dependency on gas, but not if I end up paying through the nose for it. Link to comment Share on other sites More sharing options...
J1mbo Posted February 1, 2022 Share Posted February 1, 2022 It definitely won't be cheaper than gas. Electricity carries as 25% tax (climate change levy). Link to comment Share on other sites More sharing options...
Kevm Posted February 1, 2022 Share Posted February 1, 2022 Electricity is 4-5 times the price of gas per kWh. SCOPs are normalIy 3-4 in the real world. Link to comment Share on other sites More sharing options...
jayc89 Posted February 1, 2022 Author Share Posted February 1, 2022 Disappointed but I suspected that would be the case. Thanks for the replies! Link to comment Share on other sites More sharing options...
JohnMo Posted February 1, 2022 Share Posted February 1, 2022 If you already have gas and a 32kW boiler, just hook up to your existing system, job done. Not sure why you would install an ASHP just to provide the UFH loops and keep the gas for DHW. Link to comment Share on other sites More sharing options...
J1mbo Posted February 1, 2022 Share Posted February 1, 2022 (edited) To give some numbers, the system I have fitted has be working at about 6.1p per kWh effective throughout Nov/Dec/Jan. Those are on the price cap for electricity. That's pretty much exactly equivalent with oil, which is currently about 60ppl. Design flow is 44°C at 0°C outside, so not that much different to the scenario here. Edited February 1, 2022 by J1mbo Link to comment Share on other sites More sharing options...
Andehh Posted February 1, 2022 Share Posted February 1, 2022 2 hours ago, J1mbo said: It definitely won't be cheaper than gas. Electricity carries as 25% tax (climate change levy). Government have already made it clear they are looking to reduce this on elec & apply it to gas! That being said, for OP, I'd stick with current boiler until it dies. Don't replace it for the sake of it. ASHP is a long term solution, space protect for it... But use your existing until it gives you an imperitive to change. 1 Link to comment Share on other sites More sharing options...
CotswoldDoItUpper Posted February 1, 2022 Share Posted February 1, 2022 (edited) Similarly I’ve just secured a 2yr fixed deal on my LPG for 35.7p per L inc vat. Equivalent to about 5p per kWh. Assuming my boiler is running at about 80% efficient that means the effective cost is in the region of 6.3p/kWh. Our electricity is about 22p/kWh so would need a COP over 3.5 to make any savings, let alone begin to repay the investment!* I believe mains gas is cheeper too? *it’s been a long time since maths homework time - please forgive/correct as appropriate! p.s. our boiler heats the water to around 55deg for rads/100L buffer tank. our UFH (of around 75sqm, 200mm centres over 100mm PIR between joists) runs at a flow temp of 40deg courtesy of the mixing valve. Lovely and toasty! Edited February 1, 2022 by CotswoldDoItUpper Link to comment Share on other sites More sharing options...
J1mbo Posted February 1, 2022 Share Posted February 1, 2022 36 minutes ago, CotswoldDoItUpper said: Similarly I’ve just secured a 2yr fixed deal on my LPG for 35.7p per L inc vat. Equivalent to about 5p per kWh. I’ve read this several times recently but I’m struggling to correlate this to spot or futures. It’s definitely counter intuitive thatgas delivered in a lorry could be cheaper than piped gas. Link to comment Share on other sites More sharing options...
J1mbo Posted February 1, 2022 Share Posted February 1, 2022 (edited) 3 hours ago, Andehh said: Government have already made it clear they are looking to reduce this on elec & apply it to gas! There is unlikely to be much appetite to add further to the cost of gas any time soon. We might get some relief from the CCL from electricity though. Edited February 1, 2022 by J1mbo Link to comment Share on other sites More sharing options...
CotswoldDoItUpper Posted February 1, 2022 Share Posted February 1, 2022 32 minutes ago, J1mbo said: I’ve read this several times recently but I’m struggling to correlate this to spot or futures. It’s definitely counter intuitive thatgas delivered in a lorry could be cheaper than piped gas. I thought it was cheep too! 34p + vat from Avantigas. Then my old supplier (Flogas) tried to match it and went from their initial quote of 66p + vat down to to 35p + vat per L. I thought seeing as they were close then there must be some underlying out there to hedge against! only other thing is there is a £66+vat standing charge for tank hire. Link to comment Share on other sites More sharing options...
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