mixed views: minimum flow for unvented cylinder

[spearchew]

Hello,

I've heard competing views regarding the minimum pressure and/or flow rates for unvented cylinders.

A plumber has offered to install one in my home. The pressure from the mains has been tested and comes to around 4 bars... but delivers only around 8 litres per minute (have tested all downstairs + outdoors taps).

Various manufacturers of unvented cylinders seem to indicate a minimum flow rate of 20ltr/minute. And yet it has been suggested to me by a number of sources (including a plumber) that an unvented cylinder should still perform okay given the 4 bar pressure.

Does anyone have experience or strong views either way on this?

Relatedly, I had some work done on the kitchen recently which revealed what seems to be an additional two stopcocks (see picture below). I guess these *may* be the cause of the reduced flow but... presumably the real cause could equally be narrow pipes elsewhere / underground, that I cannot possibly do anything about.

Thanks for any thoughts

 

[Mr.Stu]

I would not go near an unvented with that flow rate. Firstly the performance will be crap (For reference we just had an unvented system installed, we have 4bar incoming and 20 lt/min static pressure. The performance is good, not great, and you can just about run a hot tap downstairs, whilst having a good shower upstairs and not noticing a drop off). Secondly, if you have any issues in the future with the tank, and the manufacturer gets involved, they will just point at their doc saying "X lts/min mate".

How old is the property, is it lead pipe incoming?

Either fix the poor flow rate, or look at other systems that involving storing the water before delivery.

 

[mickyflinn]

You should ask your neighbour to do a flow test see if they get the same results but 4 bar pressue should be more than 8 litres a min flow rate.

One option would be to remove all but one stop valves especially the first brocken one incase it partially stuck to see if theres any improvement.

 

[spearchew]

thanks for your input - that's helpful

property is approximately 100 years old. Looking at the lower portion of the pipe... it appears to be lead to me (darker metal)

 

[Mr.Stu]

Time to upgrade that incoming main - https://www.youtube.com/watch?v=P1WlMxAMmx0. PITA, but if you plan on being there for 10years+, I would go through this pain now.

 

[Dandle]

The 4 bar pressure will be standing pressure with the taps closed. Its irrelevant to the cylinder performance as when the taps are open you have no where near 4bar, the 8l per minute is proof enough of that. I have put a new watermain in the last two houses I have had, the first house had a steel main but it was more than 50% blocked with limescale and this house had a 15mm pipe in which has been replaced with a 32mm MDPE pipe.