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Horizontal Hot Water Cylinders for ASHP with Energy Efficiency Rating 'A'

Domestic Hot Water & Cylinders

Last Post by JamesPa 5 months ago

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vzm56n

(@vzm56n)

New Member Member

Joined: 5 months ago

Posts: 3

Topic starter 06/03/2026 6:52 pm [#2869]

I looking to Have an ASHP installed in the near future.

My Current EPC is 'B' just 1 point short of an A.

Most HWC seem to have Energy Efficiency Rating of 'C' .

I have found Vertical HWCs with a rating of 'A' , but they are vertical cylinders.

I would like to find an 'A' rated horizontal cylinder @ 250l to fit into my loft.

Does anybody have sources/ideas?

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5257

08/03/2026 10:35 am

Posted by: @vzm56n

↑

I looking to Have an ASHP installed in the near future.

My Current EPC is 'B' just 1 point short of an A.

Most HWC seem to have Energy Efficiency Rating of 'C' .

I have found Vertical HWCs with a rating of 'A' , but they are vertical cylinders.

I would like to find an 'A' rated horizontal cylinder @ 250l to fit into my loft.

Does anybody have sources/ideas?

Horizontal cylinders are fundamentally less effective than vertical cylinders because, in a vertical cylinder, the water 'stratifies' so that the hot water is at the top and the cold water at the bottom. This means that you can continue to draw off even though much of the cylinder is filled with cool water. In a horizontal cylinder there is much less scope for this.

That said I don't know how this affects energy rating, and the obvious answer to improve it is insulation and ensuring that the pipework connected to it is both insulated and is designed to minimise loss. Several of the UK cylinder manufacturers do 'specials' so perhaps try contacting one of those. You may even find that they could do something vertical that will fit your loft, unless it is very shallow. Unvented DHW cylinders, BTW, do not have to go in an elevated position, because they are pressurised by the mains. So another thing to consider is whether there is anywhere else you could fit it.

Hope that helps.

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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vzm56n

(@vzm56n)

New Member Member

Joined: 5 months ago

Posts: 3

Topic starter 08/03/2026 7:54 pm

@jamespa

Thanks for your reply - I did not think I was going to get any feedback.!

I understand that horizontal water tanks may not be as efficient as vertical tanks and possibly the may be more problematic too!

I have limited space/height in my loft. There are no other good locations to be found in the house.

I'll see if I can get some ideas from cylinder manufacturers?

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JamesPa

(@jamespa)

Illustrious Member Moderator

Joined: 3 years ago

Posts: 5257

08/03/2026 9:37 pm

Posted by: @vzm56n

↑

I'll see if I can get some ideas from cylinder manufacturers?

Before you contact them check the space you have in the loft accurately.

In the end you have to work with the space available which may mean sacrificing a bit of efficiency! You might possibly consider two smaller vertical tanks although it's a bit of a faff and may challenge your plumber in terms of connecting up and control,

This post was modified 5 months ago 2 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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