Pipe sizing

[mrmiles]

Hi,

I have a 210L unvented cylinder with a 22mm feed coming out of it, connected to (in order)

- cloakroom hot tap (15mm tee)
- kitchen hot tap (15mm tee)
- bathroom shower (22mm tee)
- en-suite shower (22mm tee)

A plumber (looking at something else) told us that we might get a better flow rate if we upgraded this "backbone" pipe to 28mm.

I can't see how this would make a difference: the hole in the cylinder is still only 22mm, as are the feeds into the cylinder - so won't that just be a bottleneck?

Can anyone explain if there is a benefit?

I can see it might make a difference on the cold supply as that's 32mm MDPE, unbalanced (the shower valves have built-in balancers).

Thanks,

M

 

[doitall]

What the hell is a backbone pipe,

A good flow rate is dictated by pressure and pipe size, so upgrading the cold to the cylinder will help, but not make a dramatic improvement.

 

[mrmiles]

Sorry, it wasn't clear!

I meant the 22mm pipe out of the cylinder, but not the 22mm tees off it. So the outlet from the cylinder would step up to 28mm, then down again closer to the showers.

 

[Agile]

You are mis-interpreting the effect of pipe diameter and flow rate.

Water has to move faster through a small pipe.

As long as the pipes are all at least 22 mm to anything taking over 10 li/min then thats fine.

The problem is more likely to be on the cold supply side to the unvented. That needs to be at least 22 mm for best performance. Sometimes these are fitted to a 15 mm stopcock.

Tony

 

[doitall]

Sorry, it wasn't clear!

I meant the 22mm pipe out of the cylinder, but not the 22mm tees off it. So the outlet from the cylinder would step up to 28mm, then down again closer to the showers.

Same answer, some improvement is likely, but you can't get out more than you put in.