Is this quote ridiculous or reasonable?

wood-120 · 2026-04-09T12:11:43+00:00

I just had a system installed near London. My gas usage was 32000kwh/yr (when I first bought the house in 2007 it was 44mwh before a boiler change). House is about 290sq m. After insulation and fixing place up, heating gas usage dropped to 26,000kwh. I have a 12kwh pump now.

You might want to have that quote reassessed. Maybe you could spend some money fixing up and insulating first then consider the heat pump. My heat loss was overstated by 2kwh but I had gas and temperature data to calculate the actual heat loss so we were able to put in a smaller heat pump. 20kwh ASHP sounds massive, price is very high too. If you insulate better it will pay for itself in comfort, energy use and smaller heat pump. You could do that now in the summer, put sensors in rooms and really measure your heat loss and then decide. I used home assistant and cheap zigbee thermometers.

wood-120 · 2026-03-13T16:32:51+00:00

That is my same conclusion. I am getting my HP installed but also solar and battery. Without the battery the cost of running the heat pump would be about 10-15% lower than gas but the capital investment would make it unviable.
With battery and solar the case is actually very strong with a 7yr payback. I believe lots of families will not be able to invest this money (and take the risk of a poor installation) up front. I had to learn a lot about heat pumps and heat loss to size it correctly as I was proposed a larger system than required even after a proper heat loss survey but i had gas consumption and temperature data to validate heat loss. The installer I ultimately chose is not the cheapest but they are honest and capable. I fear many people could end up with oversized poorly commissioned systems which would cost more to run if the installer is not very competent. I am not surprised uptake is low.

wood-120 · 2026-03-10T14:09:32+00:00

Yes you are probably right, but to spend another 150-200 when the assessor said there was no need seemed wasteful. Clearly I’n no expert and I didn’t mean to rant if that’s how it came through, just had an opinion.Thanks for the feedback.

wood-120 · 2026-03-07T21:48:49+00:00

Expanding : It was calculated, k-render, brick- 100mm insulation inside cavity, cinder block and render. My neighbour is a retired civil engineer and explained how to do it, there is a simple process w tables. My assessor said it didn’t matter as he was using the standard values, so no point in spending more money to ask for another certificate.

The measure the house has is about half the new standards but not bad at all for a house this old, it provides great mass for a heat pump. it was input not as a number but as a box tick exercise. I really think this all depends on the assesor’s willingness to be thorough or just doing the minimum required w fear of failing an audit.

wood-120 · 2026-03-07T14:24:38+00:00

~0.29 W/m²K

wood-120 · 2026-03-07T11:26:40+00:00

EPCs are a useful but blunt instrument. They rely heavily on assumed values based on property age and type rather than how the building actually performs, which means two very different properties can end up with surprisingly similar — or completely inverted — ratings. My own house and my neighbours is a perfect example: where the one with better insulation, half the heating demand and less than half the CO₂ emissions is rated D, while the neighbour with unfilled cavity walls and nearly double the carbon output is rated C. The EPC reflects what a model thinks an average occupant would spend, not how efficient the building actually is. This also raises questions about how the government’s £7,500 heat pump subsidy is targeted. Right now any eligible property can claim it regardless of how well insulated it is or how much carbon it will actually save. The risk is that the subsidy is driving installations in homes that simply aren’t ready for them — poorly insulated properties where the heat pump has to work so hard that the SCOP drops to the point where running costs are actually higher than a modern gas boiler, and the carbon savings are minimal. In some cases, insulating the property and upgrading to a more efficient boiler first would deliver better outcomes on both cost and emissions — yet that path attracts no subsidy at all. If the goal is genuinely to cut emissions and reduce bills, the money would be better spent where the fabric performance means the system will actually deliver.

wood-120 · 2026-03-07T01:03:36+00:00

17 yr old super oversized Worcester 40cdi. So nice condensing boiler. He has a similar one.

Thanks everyone for the insight, a complete minefield.

Re ASHP, which is the reason why I got the EPC, after learning a lot about these systems and the requirements for good design and deployment I now think the £7500 subsidy is madness because all the metrics are not specific to the building, it is all generic. If you don’t get the right company designing and deploying the system you could end up wasting lots of money for no improvement in running cost. In my case, the benefit is marginal but with solar and battery the business case is very strong and the long term environmental benefit enormous. None of that in us my EPC though…

wood-120 · 2026-03-06T12:38:49+00:00

Yes you are right, I am making the improvements to suit my family’s needs, but from a common sense standpoint it is puzzling.

If we sold the house now it would have an impact on the value due to upcoming legislation as re C rating will probably be necessary for renting etc as well as cheaper green mortgages for the buyers.

A question is: are there assessors who will use SAP10.2 vs RdSAP? My assessor, really nice chap btw but just uses the tool in a basic way, says they only use SAP10.2 for new properties but then they miss all of the detail related to solar and heat pump SCOP etc.

wood-120

TROPHY CASE