Replacing knackered oil boiler with ASHP - Perthshire

DowallyDrifter · 2025-03-13T13:01:57Z

Interested in red flags, guidance on replacing 26Kw oil-boiler with in-boiler 127l HW tank, with ASHP, 300l tank. Timber frame with block exterior, 275sq.m, bilt 1999, UFH both floors with room stats in all but 3 bathrooms which are always open. Original heat loss as designed was ca. 18kW. two log burners, one in front hall one in large living room upstairs. Oil aga for cooking always on. Two suppliers quoted: one calculated heat loss at 13.3kW, the other at 18.94kW so ASHP at 16kw and 2x19kW. Both quote for buffer tank.

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Air Source Heat Pumps (ASHPs)

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JamesPa

(@jamespa)

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13/03/2025 9:38 pm

On the basis that 1l oil = 10kWh and 1cu m wood = 2500kWh, the total is between 25+10=35 and 40+10=50 MWh per annum. That's definitely in the same general ball park (dividing by 2000-2900 depending on which calculation you prefer) so I would say that the heat loss calculations are at least plausible. So basically I'm with @bontwoody

Id be tempted to consider something like a 16kW heat pump (or the largest reasonable one you can find, avoiding anything too extreme) with some backup heating for the coldest days if it turns out you need it! Or an 8 and a 10 kW or similar running either alone or together.

This post was modified 4 months ago by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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DowallyDrifter

(@dowallydrifter)

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Topic starter 14/03/2025 8:38 am

@abernyte thanks tbh I was more thinking about bolstering the insulation within the timber frame which would entail removal of plasterboard etc. and a massive amount of disruption.

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