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Heat Geek mini store vs pump size

Air Source Heat Pumps (ASHPs)

Last Post by Tomtheheatingengineer 2 months ago

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RobH

(@robh)

New Member Member

Joined: 4 months ago

Posts: 1

Topic starter 07/07/2026 6:15 pm [#3089]

Hi All.

Ive recently had a home survey done with Heat Geek and they returned a heat loss of 3.8kw, for our 3 bed 1 bath end of terrace home. The computer quoted a 7kw Valiant Pro with a 110l Mini store.

Im slightly perplexed by the size of the pump quoted as i didn't think it needs to be this big to compensate our relatively small heat loss plus a not very big cylinder either.

Has anyone experienced something similar or can offer any advice? I have asked the same question to my installer but yet to receive an answer.

Thanks Rob

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Tomtheheatingengineer

(@tomtheheatingengineer)

New Member Member

Joined: 2 months ago

Posts: 6

23/08/2026 6:33 am

Hi Rob,

For context I am Heat Geek installer, It has most likely suggested a 7kw to size it for the hot water demand, the 110L @7kw will run for approximately 12ish minutes constantly @ about 40 degrees. This allows for 2-3 people to use a single shower on average.

You can find the information I have quoted here:

NEWARKCYLINDERS.CO.UK "https://newarkcylinders.co.uk/wp-content/uploads/2025/11/Heat-Geek-Mini-Store-v1.4-Specification-Installation-Booklet-Nov-2025-1.pdf"

Hope that helps!

This post was modified 2 months ago by Mars

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 4 years ago

Posts: 5602

23/08/2026 10:38 am

Posted by: @robh

↑

Hi All.

Ive recently had a home survey done with Heat Geek and they returned a heat loss of 3.8kw, for our 3 bed 1 bath end of terrace home. The computer quoted a 7kw Valiant Pro with a 110l Mini store.

Im slightly perplexed by the size of the pump quoted as i didn't think it needs to be this big to compensate our relatively small heat loss plus a not very big cylinder either.

Has anyone experienced something similar or can offer any advice? I have asked the same question to my installer but yet to receive an answer.

Thanks Rob

When looking at 3-4kW houses its also worth bearing in mind that most manufacturers dont sell anything smaller than 5kW (sometimes they sell a heat pump badged smaller but its almost always simply a larger one downrated, which is of no advantage). Also Vaillant heat pumps seem pretty good from what I have seen at coping with oversizing.

I would say that, if you are using a mini-store (presumably because you haven't got room for a larger cylinder), the suggesting made is both understandable and defensible. If you had room for a larger cylinder then the 5kW would, prima facie, be a better choice. All engineering requires trade-offs!

This post was modified 2 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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Tomtheheatingengineer

(@tomtheheatingengineer)

New Member Member

Joined: 2 months ago

Posts: 6

23/08/2026 5:53 pm

Posted by: @jamespa

↑

Posted by: @robh

↑

Hi All.

Ive recently had a home survey done with Heat Geek and they returned a heat loss of 3.8kw, for our 3 bed 1 bath end of terrace home. The computer quoted a 7kw Valiant Pro with a 110l Mini store.

Im slightly perplexed by the size of the pump quoted as i didn't think it needs to be this big to compensate our relatively small heat loss plus a not very big cylinder either.

Has anyone experienced something similar or can offer any advice? I have asked the same question to my installer but yet to receive an answer.

Thanks Rob

When looking at 3-4kW houses its also worth bearing in mind that most manufacturers dont sell anything smaller than 5kW (sometimes they sell a heat pump badged smaller but its almost always simply a larger one downrated, which is of no advantage). Also Vaillant heat pumps seem pretty good from what I have seen at coping with oversizing.

I would say that, if you are using a mini-store (presumably because you haven't got room for a larger cylinder), the suggesting made is both understandable and defensible. If you had room for a larger cylinder then the 5kW would, prima facie, be a better choice. All engineering requires trade-offs!

Yes I agree, that’s why Heat Geek have most likely selected the 7kw as it will still modulate low enough but provide enough power for the mini store. If the minimum modulation causing a little too much cycling then a volumiser could be added relatively easily.

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