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Hot water cylinder - 1 or 2 cold feeds from loft?

Postby DIYNovice2020 » Sat Apr 18, 2020 1:21 pm


Looking for advice please. Is there benefit having 2 x 22mm cold feeds from loft CWS tank(s) into same direct vented HWS cylinder? This set-up I inherited with a feed either side at the bottom but am looking to have the HWS cylinder moved and replaced.

Have any of you come across such before and are there any benefits it provides? One reason for asking is that I have had two different views from plumbers – one “leave as is”, the other “its overkill”!

Let me explain further!

Our property has a Direct Vented HWS Cylinder over 30 years old. I want to relocate this but will buy new due to its age/condition etc. The cylinder is not used for heating – there is no gas, only electric storage heaters. Due to previous point, I am happy to stick with a gravity fed direct vented system.

The current HWS cylinder is 150cm x 40cm and has top draw off as well as a dedicated connection for a pumped shower on the front.

However, what is different are 2 large CWS tanks in the loft (both >200L) and 2 x 22mm cold water feeds - 1 from each CWS tank which are interconnected - into the bottom of the same HWS cylinder – one either side.

Previous owners had a 4.0 bar pump which fed a bespoke shower unit with ceiling and side jets – aka it used a fair amount of water hence the 4.0 bar pump and 2 x cold feeds.

We now have a more simple installation - a Mira Vision Pumped Shower – this recommends CWS tank of >230L. The maximum flow rate of the shower is 16L/minute but this can operate at same time as bath fill/other household use.

I don’t envisage wanting something as powerful as 4.0 bar again. Is there any advantage having 2 x 22mm cold feeds into the HWS cylinder – and keeping the 2 large CWS tanks in the loft? I was looking at ‘downsizing’ to 1 x CWS tank in the loft – either 50 Gallon/227L or 70 Gallon/318L.

I understand the 22mm feed from CWS can flow at ~0.6L/sec (36L/minute) so this seems to be sufficient to replenish the HWS cylinder if there are multiple concurrent uses? Otherwise, would it be better to consider 28mm feed from the CWS tank?

Thanks for your help.
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Simply Build It

Postby stoneyboy » Sun Apr 19, 2020 9:14 pm

Hi diynovice2020,
Presumably you can turn off the feed from each of the CWTs. Suggest you turn off one and try running the bath and the shower and perhaps kitchen tap and see whether there is any indication of supply starvation.
This will answer your question as to whether one 22mm cold feed is sufficient.
Regards S
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Postby DIYNovice2020 » Mon Apr 20, 2020 12:30 am

Thanks stoneyboy for taking the time to reply.

Unfortunately both gate valves between CWS and HWS no longer work :-( Was trying to avoid replacing these but doing so would allow such a test. Other option would be to isolate one of the CWS tanks but would need to drain it sufficiently to add bungs into the bottom of the CWS (due to both being interconnected) and stop cold mains feed into the 'unused' CWS tank :-)

Just curious as to how many people have seen two cold feeds into Direct Vented HWS cylinder before as you cannot seem to buy such unless custom drilled etc.

Thanks in anticipation of any more views.
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Postby kjones1829 » Thu Apr 30, 2020 6:24 pm

I think you should replace the gate valves between CWS and HWS. And then head on to stoneyboy's advice. It is just to avoid any more complications.
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Postby DIYNovice2020 » Thu Apr 30, 2020 7:37 pm

Thanks kjones1829 (and stoneyboy) - yes, makes sense and at least gives me some benefit of isolating the CWS from HWS in the meantime.

Thanks for the replies.
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