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Estimating true heat loss from twelve months of consumption data

ian33a · 2026-05-14T06:13:42Z

We have an old house, mostly with stone walls, 288 square metres and heated with oil. That said, it has hydronic under floor heating throughout most of it, as well as reasonably insulated roof spaces, some internal stud walling (with assumed insulation behind) and double glazing throughout. The latest EPC was over 13 years ago and it came out as grade D. I suspect that this was done prior to some of these upgrades (by the previous owner). We typically run our heating at 18 degrees throughout the house (with a 2 degree set back over-night) and leave it running constantly throughout the winter months between about October and May. We also heat domestic hot water using oil most of the time, although I do use the immersion if there is a battery surplus from solar (Generation based FIT) or if the Agile rates are cheaper than the cost of oil. It's not to say that we would jump at moving to a heat pump immediately but, with the current cost of oil and the increase in BUS grant, the argument to do so has become more compelling. If I go to the heat geek site, the estimated heat loss is about 19KW and it's hard to get them excited about our house unless we pay for a bespoke black label service. With an 18KW heat loss calculation and concerns about installers and poor SCOP achieved, I wonder if riding out Trump's warmongering and hoping that the cost of oil will drop is a better proposition. That said, if I do the maths using a formula that I found on another thread on this site, with our oil usage over the past 12 months, being about 2010 litres, we would need a heat pump of around 8KW. I do appreciate that an accurate figure only comes from a proper heat loss survey and this, quite rightly, involves time, effort and the use of software which needs to be paid for. I wonder though, why the on-line estimate is twice as much as what appears to be real use data - are our delta T's different, are incorrect assumptions from an out of data EPC being used or is it something else? Your thoughts are welcome. thanks.

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ian33a

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Topic starter 20/05/2026 7:28 pm

Thanks - something to certainly consider !

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