sharpener

Do you need to have it done to maintain the warranty? £200 - £300 is not unusual. Otherwise DIY as above, also clean any Magnaclean or Y-strainer filters etc. Inspect for leaks. Check glycol concentration if used and system pressurisation. Check condensate drain is free. Crack open the pressure relief valve.

Sounds expensive, what part of the country? You can price it as a complete kit on the Midsummer Wholesale website. IIRC cooling was not allowed under the BUS scheme, I can't find a reference so best to check on the OFGEM web site. The Arotherm plus needs a plug-in coding resistor to do cooling, over £200 UK retail but you can import them from the EU for less, I have read it is the same resistor as fitted to gas boilers for some purpose (presumably not cooling).

As someone else in the SW peninsula I would have thought you too were exposed to >1000 mm rainfall/year<g>. Yes, when there is sun OH likes to use the rotary airer for "freshness" but I don't see much point, now we have kitted out the second roof we have 6.9 kW of PV which gives us a surplus most times of year.

Which means that you can't get the 70C plus flow temp that R290 brings. Midsummer Wholesale has this wonderful typo: *For Vaillant aroTHERM Split systems we will require evidence of your F-gas certifiction*

I think this is a retrograde step and shows how little the politicians know about the science. Another of HMG's perverse incentives, they delay the surcharge on gas boilers but then tip the balance back towards HPs with this. Not sure I would want cavity wall insulation (if I had wall cavities). But loft insulation is a total no brainer, the ROI is better than almost anything else you can do and it might reduce the size of HP you need as well so in that case essentially free.

https://www.vaillant.ua/downloads/proekti/0020222099-10-compressed-2406863.pdf?fbclid=IwZXh0bgNhZW0CMTAAAR2cgInGE7BtvCgpdxYDszZUgKRAQE8jm3AIb_4C0KwHKwd_pHVLc5itfYA_aem_AaxrDlhR_6iT7VEGsQhhKVj5KjwLaeJTS-GNzLG_Gy5tBQRLd1zxg8__lVP42DpLQzO2V26rFwsW0FhdKIEFWMSo

No. Most Vaillant installers I have spoken to do not know they exist. Nor did the V regional tech mgr for the SW. I have not found any explanation for why they are not available in either English or German (which I can read well enough). There is also a Planning your Installation doc of which the EN and DE versions are very different, it's all rather a mess, on the FB page there have been various discussions about this.

You can download the full set of tables from the Arotherm FB page here starting at p34. So I can't see any way the 5kW model would satisfy this even with massive rads and a flow temp of 30.

Heatpunk gives 7763W as the output at 53C flow and -2.3 OAT. So by choosing 53 not 45 as the flow temp it would still more than match the heat loss, and you might well need fewer radiator upgrades and maybe saving more in capital than you would lose in running costs. You will probably not find an MCS installer willing to do this though. When I lived in Hitchin there was snow on the ground for some weeks in I think the winter of 1968 - 69, but it was most unusual, I don't suppose you will see -2.3 very often nowadays.

That's probably why they "highly rate" them! Also as an umbrella provider it de-risks the relationship with the actual installer.

FWIW I received this comment from @mk1_manyesterday: "Air2heat highly rate Panasonic units especially the new R290 versions." They operate an MCS umbrella scheme and are in Shropshire.

I don't think we even had EPCs 20 years ago, this article says they were introduced on 1 August 2007. Michael Podesta's blog on predicting HP size from gas consumption dates from 2022, and the extension of the idea to EPCs first appeared yesterday AFAIK.

Do you have a reference for this? It was new to me. Yes. If for example you are looking at houses to buy they will have to show you (or you can look up) the EPC and from this you might then get a fair idea of HP size. As you also could using the Heat Geek cheat sheet. And then you could work out where it might be sited. (The installers who came yesterday are proposing a big Stiebel Eltron mounted over a passageway on wall brackets). But you cannot retrospectively ask for a year of weekly meter readings to be done, at most you might get quarterly gas bills and of course in that case the result would be more accurate than using the EPC.

The three that you have to extrapolate in this seem to be rather different from the first three so I would be a bit sceptical about using them but I suppose taking the median helps. I take it these are perhaps smallish ?terraced houses (or maybe bungalows) of identical floor area? In which case an HP of 0.4 x 5.9 = 2.4 kW sounds plausible, whereas your 1 does not.

Well clearly if you have got all the underlying data then it is of course better to use that in Jeremy's Spreadsheet or Heatpunk or Heat Engineer. I have been impressed by Michael Podesta's use of degree-days to calculate HP size from gas consumption. Essentially this method just estimates gas consumption from the EPC figures which can then be used to imply a certain HP size. The old GINO adage always applies, Garbage In Nonsense Out.