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How Accurate Is My DIY Heat Loss Calculation?

kilgorexv · 2026-08-23T19:05:28Z

Tragically i was a little bored and under the weather at the weekend so in preparation for going out for quotes for a heat pump and cylinder i had a go at my own heat loss calculations.... any thoughts and advice appreciated. Individual bits.... the end of our hall is a wood and glass wall leading tot he porch so i have ramped up the u fadctor considerably. ?

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Air Source Heat Pumps (ASHPs)

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kilgorexv

(@kilgorexv)

Active Member Member

Joined: 5 months ago

Posts: 17

Topic starter 30/08/2026 8:44 pm

@old_scientist i dont but i want to be able to reasonbly replicate what an installer will produce so i can unserstand any proposals.

This post was modified 2 weeks ago by kilgorexv

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AndrewJ

(@andrewj)

Reputable Member Member

Joined: 2 years ago

Posts: 245

30/08/2026 8:54 pm

@kilgorexv definitely a larger inverter will help and more PV will help support your usage in winter - we have 10kW of PV split across east and west and even on a cloudy day it would cover background load plus a bit. DNOs have started restricting both export and inverter sizes so it’s worth upgrading those as soon as. Our export limit is 3.68kWh but with some planning we can avoid clipping except for an hour or two on the sunniest, mid-summer days. It all helps towards a -£7 bill last year!

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Batpred

(@batpred)

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Joined: 2 years ago

Posts: 1153

04/09/2026 7:18 pm

Posted by: @andrewj

↑

It all helps towards a -£7 bill last year!

That's great! I think we managed to get to that last month (no PV) but the heatpump will easily change that as winter approaches.

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kW export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; Vaillant Arotherm Pro 7kW; 100Amp head, HA lab on mini PC

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AndrewJ

(@andrewj)

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Posts: 245

04/09/2026 8:41 pm

@batpred I suspect it will be more this year. I had 9 months at 15p export and just 3 months at 12p. This year it’s likely to be 12p all the way, although it could come down again I suppose. 3p doesn’t sound like much but it all adds up! Still, I pared to £2100 a year, it’s a massive saving.

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