unvented hot water cylinder

1 Apr 2009
Reaction score
West Midlands
United Kingdom
I have an unvented hot water cylinder 150 litre. We use two showers normally and the flow and pressure seem adequate. We are now adding a third shower with a shower panel with body jets. The recommended pressure for this is 2 Bar. I am not sure our UV cylinder which is kept near the kitchen will be adequate. I understand shower pumps are not suitable. What is the best way to boost the pressure?
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Think you will struggle to use 3 showers with it lack of water quantity,
but if you are still using the same amount of water i:e your using the new one and using one of the others less then you may be ok.

seems a small tank though.
for a start most vented cylinders operate at 3.5 bar. secondly whats the chances of all three showers working all at once???? unvented cylinders must be feed by the incoming water mains, which is normally well over 3 bar, but the supply to the cylinder must be 22mm copper, other wise you may experience a lack of flow at the outlets. most dwellings are supplied with only 15mm water mains supply. if u run ur two current showers along with say two other sinks or a bath and the flow rate is still good at all, then go ahead with ur new installion. does that make sense??? :)
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advancedplumber wrote "
Unvented cylinders must be feed by the incoming water mains, which is normally well over 3 bar,"

Thats an unwise assumption to make the water authority have a statutory requirement to supply water to the main stopcock at 1 bar (equal to 15 psi). many parts of London only get say 1.5 bar however it is very subjective to where you live and the altitude. For example Frensham in Surrey has 11 bar on the main as they have to pump it out of farnham up the hills.
Tongham surrey has 7 bar.
But imagine a street where the incoming is 1.5 bar and its a street of 1 bedroom flats apartments, everyone either got a combi boiler or an unvented cylinder on electric what do you think happens to the water pressure at peak times say 7.30 am ?

Oh while we on subject "for a start most vented cylinders operate at 3.5 bar" the primary coil on a standard vented cylinder will fail at 3.5 bar.
i assume he meant unvented :p
The operating pressure of an unvented cylinder is set by the incoming mains pressure so if it 2.25 bar like mine is it runs at that. However when the 4 foot main burst in center of town last week my incoming gauge said 0.5 bar and it was trickling out.

Back to gowri... it unlikely you gonna be using 3 showers at once because you would empty that tank in like 5 minutes.
A stuart turner 1.5 bar shower pump will empty a 150 ltr cylinder in 6 mins flat. your only option is a larger tank and possibly and accunmulator.

we quite frequently go down this route in country houses and houses that have 4-5 bathrooms.
Many parts of London like Willesden have a mains pressure closer to 1 Bar static pressure at ground level.

Take that up to the second floor ( English ) and its down to about 0.5 Bar!

I was told in Warwickshire that they only had to supply 0.6 Bar static and 6 litres per minute open pipe!

In Kings Cross I am helping a Chef who has a cafe with two flats above. The cafe gets about 3 li/min open pipe and the flats about 1-2 li/min.

The street has been dug up about six times in the last four months, often as a result of serious leaks flooding the road a few days after the last repair was completed.

Its not that good at street level ! Where is Thames Water?


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