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Peering over the ASHP cliff

GrahamB · 2022-12-18T11:01:05Z

My gas boiler is as old as the house - twenty six years. We have a good local maintainer (Sole trader) who has looked after us for twenty five of those years. The boiler is reliable. The house is a four bedroom detached house which had a loft conversion twenty years ago giving us two extra rooms and reduced, yes reduced heating costs. The total floor area is around 144sq/m. We also have solar panels (7) which are eleven years old and one of the first to benefit from FIT payments. The upfront costs were cleared years ago so everything they generate now is pure profit. I’m now wondering whether we should simply upgrade the boiler or take the risk and invest in an air source heat pump. To replace the gas boiler would cost around £2,500. To go the heat pump route would cost around £8,000. We’re both retired. The house is big for just us but we enjoy having people stay. I have two indicative quotes, one suggests a Daikin 9kW Monobloc, the other a 16kW Samsung! These are based on information given online only. To me, that’s already quite a difference. One company offered a free heat loss survey, no obligation. The engineer visited back in October and I’ve heard nothing more from them despite a number of phone calls and e-mails. They simply stopped replying. So that makes me wary – better the devil you know, etc. Then there are the running costs. On 12th December, when it was really cold, my tired old boiler cost less than £18 to keep us warm and heat the water. I say less because we also cook with gas but I can’t split that out. I’m reading about ASHP daily costs far in excess of that which again makes me wary but most lack the context of house size, family size, quality of insulation and of course, age of the installation. I also understand that an ASHP is better running 24/7 which, as we age, would be better for us. So, if you was starting out on this journey, what questions do you wish you had asked but didn’t? Is there anyone who can identify with my size of house and reassure me regarding running costs?

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Air Source Heat Pumps (ASHPs)

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Oswiu

(@oswiu)

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19/12/2022 8:36 am

@grahamb that all seems quite reasonable then for the 9kW quote. My pipe run for my monobloc is about 10m there, 10m back. The manual does allow longer pipe runs with careful design, but generally if you're having a long pipe run you'll want a split system which is when the refrigerant is pumped inside and heats water once inside the house in a box on the wall. They require a bit more space inside, but less outside, and they also need to be installed by an F Gas safe engineer so I think they're getting less popular.

I got hit with additional fees of about £1k for long cable and pipe runs. I suggest if they haven't taken that into account and they want to add a cost on that you think about hiring a third party electrician.

That 19,309kWh will be delivered heat, not electricity, so that's the part that would end up being roughly the same as your gas bill. I wouldn't worry if it's much higher or lower, just assume it'll be similar. They'll have probably estimated electricity usage to be between 5,000 and 6,000kWh for the heat pump.

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GrahamB

(@grahamb)

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Topic starter 19/12/2022 9:21 am

Posted by: @oswiu

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That 19,309kWh will be delivered heat, not electricity, so that's the part that would end up being roughly the same as your gas bill. I wouldn't worry if it's much higher or lower, just assume it'll be similar. They'll have probably estimated electricity usage to be between 5,000 and 6,000kWh for the heat pump.

Wow! Using your lower figure, that's going to ADD around £400 to my energy bill, using the higher number, that's £853 and that's totally ignoring the gas cooker.

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Oswiu

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19/12/2022 9:27 am

@grahamb yes but you use less gas than that. Take your gas usage in kWh and divide it by 3 or 4 to get your heat pump usage. I think a gas hob normally accounts for only about 1 or 2% of your gas usage so you can basically ignore it

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GrahamB

(@grahamb)

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Topic starter 19/12/2022 9:47 am

@oswiu I'm a little confused now. Earlier you indicated my electricity usage would be around 5-6,000kWh for my heat pump. I used those numbers?

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Oswiu

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19/12/2022 10:06 am

@grahamb I was saying they may have estimated that from guessing your heating/hot water needs at 19000kWh. If your needs are lower than that, which it seems like they are, then you won't use that much.

They may have given you an estimated 'efficiency' across the year called SCOP or COP or SPF which you can divide your actual gas usage by to get estimate electricity usage. It'll probably be between 3 and 4. The lower the flow temp is (and the bigger your radiators), the bigger this number will be.

When you say they included an 18L vessel in your quote, you should ask them if that's an in-line volumiser or buffer. If it's a buffer you should ask why you need it since they can sometimes be useful but also lower efficiency.

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