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Starting Our Heat Pump Journey: 1962 build 3 bed detached house

Ian S · 2026-08-11T17:50:15Z

Hi We are just starting our heat pump journey, we have a 1962 build 3 bed detached house which has the usual large windows. We did a fair amount of upgrades done when we moved in 15 years ago, re wire, replacing an old floor standing gas boiler with numerous radiator changed from poor performing ones new hot water cylinder and moving to a sealed system, A classified double glazing etc. We have solar and 10kW battery storage and run 2 ev’s. We have had someone from ARIA to do the initial pitch, lots of videos, slideshows etc and an initial estimate subject to survey. Main concern is their design includes a buffer tank which seems a bit overkill and watching numerous YT videos question their use. Current recommendation is a 6kw outdoor unit and 250l cylinder. Heat Geek certified installer coming on Monday to do a survey so should get an idea of heat loss and a better idea on cost over initial online estimate. Did the initial online quote with Octopus, energy provider, requested a call but currently finding it impossible to get anyone to talk to me. Was hoping to get a rough idea of amount of energy used by their heat pumps to get an idea if it is worth increasing my solar battery storage. Looking for any recommendations for the Reading area for us to consider as it looks like we won’t be having Octopus through the door now. Sorry for the long intro. Cheers Ian

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Air Source Heat Pumps (ASHPs)

Last Post by JamesPa 1 hour ago

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JamesPa

(@jamespa)

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18/08/2026 7:53 am

Posted by: @ian-s

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@jamespa many thanks for your thoughts, my gas usage for last year was 9309 kWh, 2024 was 9655 kWh, 2023 was 9011 kWh. Most of this would of been heating as we use air fryers and slow cookers a fair amount.

@ian-s

Assuming your house is tolerably warm most of the time (ie that it doesn't cool more than say 2-3 degrees during and 'setback' period), that clinchs it. Those consumptions indicate something around 3 to absolute max 4.5kW; the 5kW device should be fine (the classic calculation, which is science based and applies to much of mainland uk, is to divide annual consumption by 2900 to get loss). If your house does cool a lot then it might be more, and if you give some idea of the amount and pattern a rough correction can be calculated. Most likely it will still work out sub 5kW.

This may also help us understand why not many rad upgrades are needed. The rads may be sized to fit the windows not the required output, so are currently well oversized.

With the caveat about house temperature, and a couple more questions as @mars suggests, i would say this is sufficient evidence to proceed. If you want more assurance still you need to plot daily gas consumption against average outside temperature, preferably in a year when you operate your gas boiler as close to like a heat pump as it allows. That's actually what I did, but my house was borderline 7kW not (subject to the comment about temperature) obviously well sub 5.

This post was modified 1 hour ago 3 times 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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