In article , Dave
writes

"Dave" wrote in message
...
I'm told we have a 20mm "poly" water feed to the house, it goes-in to a
15mm
stopcock and then 15mm around the house. The pressure and flow rate at the
upstairs cold tap (mains fed, not gravity!) is very good.
As part of a move to a mains-pressure hot water system it's been suggested
that the stopcock and pipe to the cylinder should be changed to 22mm to
"improve the flow rate" - how can this be?
I would have thought that the limiting factor was the pipe run from the
main
to the stopcock and if this has a bore of somewhere near 15mm it doesn't
matter what I do in the house. Am I wrong? Is there any benefit in using
larger pipes downstream of the stopcock?
It all depends of the relative lengths of the pipes. 20m of 15mm internal
bore will have a greater opposition to flow that 10m of same. If you had
10m of 15mm internal bore outside & 10m of 22mm inside, the opposition
to flow would be less.

If your current internal plumbing is in 15mm then you can get a feel for this
by opening the stopcock fully & doing a timed fill of a 2 gallon bucket from
the closest tap to the stopcock, then repeat for the furthest tap from the
stopcock. If it's far slower then think about changing, otherwise not.

As to the pressure thing, is it really pressure you are interested in or flow,
ie. can I get a healthy shower and can I fill the bath in a reasonable time.
You should be able to get a feel for this by filling the bath with cold only or
rigging up a temp shower head with cold feed only.

Btw, I wouldn't plumb my hot flow on a mains pressure system in 22mm
as it would delay the arrival of hot.

ps: a 20mm poly incomer is tiny . . . .

Dave S

Forgot to ask ...
Is there an easy DIY way to measure the water pressure?

Dave S

--
fred