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Heat loss calculations and how they work in conjunction with heat pump sizing

Mars · 2024-09-25T15:47:11Z

Kicking off a New Thread: Heat Loss Calculations We’ve just released the latest episode of Homeowners’ Q&A, where we dive into heat loss calculations and their importance in sizing heat pumps correctly. Our panel – featuring Michael Crook from Heat Pump Installers UK, Graham Hendra, and @jamespa (from the Renewable Heating Hub community) – discusses why accurate heat loss calculations are critical to ensuring your heat pump is the right size for your property. We cover common issues that arise from inaccurate calculations and how homeowners can avoid costly mistakes. James shares his personal story of how incorrect heat loss surveys nearly led to an oversized and inefficient heat pump installation. Special thanks to One Heat Loss for sponsoring this episode. They specialise in providing independent heat loss calculations for both homeowners and installers. For more information or to take advantage of their special offer for Renewable Heating Hub members, email your plans to info@oneheatloss.co.uk, mention Renewable Heating Hub, and receive an automatic discount! Got questions about heat loss calculations? Drop them below.

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upnorthandpersonal

(@upnorthandpersonal)

Eminent Member Member

Joined: 3 months ago

Posts: 26

12/02/2026 2:44 pm

Posted by: @jamespa

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If you want to store in a tank for later space heating you would need a much bigger tank and different pipework. Its possible in principle but the scale of storage needed makes it difficult or impossible in practice.

Yes, you need something like this:

This kind of set-up is very common in places that use wood boilers here in Finland. The tank you see in the picture (the white/red cylinder) has a capacity of 3000L. The picture was taken while I was installing the wood gasification boiler (the red thing in the middle) and heat pump at my house. i can store heat for several days for both heating the house and hot water.

My blog where I write about all the systems in place and decisions made for my off-grid house at 63 degrees north in Finland.

👍

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 4920

12/02/2026 3:03 pm

I love it.

In a UK context, the space that the cylinder sits in is the size of a bedroom, which in the South of England affects the house price by north of £100K (for some reason we sell houses principally by number of bedrooms not floor area, which, together with sky high land prices, incentivises tiny rooms in small houses).

Also even if you can get 55C of useful temperature drop out of it (heat to 95, cool to 30) it stores only 190kWh, enough for an not atypical 8kW house for a day. (We didn't, until relatively recently, bother to insulate our houses, because we have a mild climate and very cheap gas/coal - our gas is still very cheap).

This post was modified 3 months ago 2 times by JamesPa

This post was modified 3 months ago by Mars

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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upnorthandpersonal

(@upnorthandpersonal)

Eminent Member Member

Joined: 3 months ago

Posts: 26

12/02/2026 3:17 pm

Posted by: @jamespa

↑

Also even if you can get 55C of useful temperature drop out of it (heat to 95, cool to 30) it stores only 190kWh, enough for an not atypical 8kW house for a day. (We didn't, until relatively recently, bother to insulate our houses, because we have a mild climate and very cheap gas/coal - our gas is still very cheap).

For reference, my house heat loss only gets to 8kW with an inside temperature of 22C when it's -40C outside...

My blog where I write about all the systems in place and decisions made for my off-grid house at 63 degrees north in Finland.

👍

😂

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AgentGeorge

(@agentgeorge)

Estimable Member Member

Joined: 1 year ago

Posts: 172

12/02/2026 7:57 pm

@jamiejones85mespa your comments are spot on with my thoughts the past few years. As energy prices soared, id decided to invest in Solar and a Heat Pump.i decided to insulate everywhere I could, floors and new walls are 150mm to code. The extension surrounds the house and Ive noticed heat is trapped in side the old part of the house. I insulated the new extension roof with 150mm and now adding extra insulated plaster boarding to the exterior walls in the old rooms in the house. New ceilings downstairs are being insulated with 100mm rockwool to stop heat migrating upstairs and added sound insulation to walls with the Heat Pump close to it.ive been tweaking the system settings for a year and have gradually improved the COP from 3 something to high 4’s and this week I achieved my first 5