March 4Mar 4 This is ours heated via 3kW immersion. 210L slimline cylinder. Temp messing about 1/3 up from bottom. Basically 1hr or 3kWh to heat.
March 5Mar 5 18 hours ago, Selfbuildsarah said: 🤦♀️🤦♀️🤦♀️ Anyone know a good installer in Cambridgeshire? @Dreadnaught may know one?
March 5Mar 5 20 hours ago, JohnMo said: Our Haier 4kW will kick out over 6kW, even though the datasheet doesn't state it does. So will easily heat a big cylinder. But we use the immersion. Wow even at low temperatures? I assume the 4kW and the 6kW are essentially the same units with some software limit applied
April 6Apr 6 Author I’ve finally got around to looking at the heat loss figures and roughly calculated that the suggested size of heat pump by our installers is too large. They have told us 12kw but my calculations said 7kw. I will do a room by room calculation to double-check but I wondered if some kind soul has the time to check for me if I send my SAP report. I simply can’t get on with the online checkers. Would be so grateful.
April 6Apr 6 43 minutes ago, Selfbuildsarah said: but I wondered if some kind soul has the time to check for me Just post the figures here, redact any address details, and I am sure someone will give it a look.
April 6Apr 6 1 hour ago, Selfbuildsarah said: I’ve finally got around to looking at the heat loss figures and roughly calculated that the suggested size of heat pump by our installers is too large. They have told us 12kw but my calculations said 7kw. I will do a room by room calculation to double-check but I wondered if some kind soul has the time to check for me if I send my SAP report. I simply can’t get on with the online checkers. Would be so grateful. Better if you can send a dimensioned copy of the floor plans and elevations together with all the U-values for the elements - windows, doors, internal/external walls, floor, ceiling, roof, etc. - and the design air permeability or test results in q50 and any MVHR specs. Then privately share your postcode. If I have all these details I can run a fully BS EN12831 heat loss calc to current MCS standards which not only provides a heat generator loading, but also the room loading based on calculated air permeability. I can then also provide initial figures for any underfloor heating design and requirements together with flow temps & floor surface temps assuming that's what you're having. I have a tool that will soon be available free for self-builders, but I'm currently working through final bug fixing and hosting, so it's going to take a few weeks until it's online. Please feel welcome to send me a PM.
April 6Apr 6 3 hours ago, SimonD said: I have a tool that will soon be available free for self-builders, but I'm currently working through final bug fixing and hosting, so it's going to take a few weeks until it's online. Sounds very interesting!
April 6Apr 6 5 hours ago, Selfbuildsarah said: but my calculations said 7kw If your a new build that is pretty airtight with MVHR and decent insulation, unless the house is 400m² I doubt 7kW is correct, especially near Cambridge.
April 8Apr 8 On 06/04/2026 at 18:47, MikeSharp01 said: Sounds very interesting! I don't want to hijack this thread, but here are some screen shots. The app will be open source with repo on GitHub of course. Problem is I keep on thinking about additional functionality and adding that after customer questions so I need to be more disciplined and release a version 1 I can then build on rather than continuously develop!
April 8Apr 8 Blimey that looks really good - looking forward to trying that out. PS in my day job I'm often testing functionality of new software
April 8Apr 8 25 minutes ago, marshian said: Blimey that looks really good - looking forward to trying that out. PS in my day job I'm often testing functionality of new software Oh, nice, hopefully you can give me lots of feedback!
April 9Apr 9 On 08/04/2026 at 13:40, SimonD said: Oh, nice, hopefully you can give me lots of feedback! I'm also happy to test (and have done software design, development and testing in previous life). Plus this will be useful for my needs as like the OP, I have had a ASHP proposal that seems ridiculous (16KW) given the energy efficiency intended for the house - even if it is on the larger side.
April 9Apr 9 On 06/04/2026 at 19:48, JohnMo said: If your a new build that is pretty airtight with MVHR and decent insulation, unless the house is 400m² I doubt 7kW is correct, especially near Cambridge. I'm working in Cambridge next week. Are you saying to leave my thermal budgie-smugglers at home?
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