Getting info on upgrading the water supply to feed a new combi. Going to
replace the old lead pipe with newer blue plastic. Waterline are putting
22mm from the mains to our stopcock. Some-one has suggested to hubby that
we put in 25mm from there and reduce it back to 22mm at the boiler.
Would this really increase flow rate? IF so can some-one explain the
science of that?
..also depends on the length of pipe.
When we changed to 32mm plastic over 500m and down to 22
for 10m the flow and pressure was so high that a pressure
reducing valve had to be fitted. !
If you live in a hard water area with 'crudded up' 3/8 int bore
lead + leaks you'll be amazed at the difference in flow when
changing to plastic. .. 22 / 25mm for a few metres wouldn't
make any difference.
Recently fitted a new combi and new supply to the house from the 4" main the
other side of the road.
Water board said they normally fitted 25 mm blue plastic to the meter at the
boundary and sugggested
I continue on with 25 mm as far as possible. This I did and used 22mm copper
and full bore shut off
valves where needed. I also de-burred / radiused all pipe edges very
carefully and used minimum
number of joints and bends throughout.
Old system was 100 year old steel (iron ?) pipe which actually looked in
fair condition internally when
I cut some bits open - pressure is 4 bar - Original flow rate at bath tap
(22mm) was 15 litres a minute.
New pipeworks installed.............
Flow rate is now 45 litres a minute and the combi shower is approx 19 litres
Fan-blinking-tastic shower - in fact, I replaced the 11 mm bore shower hose
with the smaller 7mm (?)
which still gives 15 litres a minute to save water and gas but is still the
best shower I have had.
(Using the Wickes 30 Kw combi - also good / recommended!)
Summary - use big bore where possible to maximise flow rates with good
Not expecting the cold flow rate to reduce in winter - the hot rate I also
be little affected as the boiler is currently modulating at the moment -
granted it is
only raising the water at the moment by about 20 deg C, but the cold intake
will only drop by another 5 or 8 degrees and then I guess the boiler will be
full output. I like my shower at about 37 deg C (Cool) which helps flow
Thank you very much for all your replies. Our kitchen, where the water
supply comes in, is only about 20 foot from the mains on the pavement, so I
suppose it will make little difference to us.
PS does ALL the water for the house go through the condensing boiler, ie the
cold too, or is it a matter or choice? Seems to be different info with
PPS The central heating pipes are visible - no to bad in the living room
they are behind the curtain, but they look a sight in the kitchen, even
though they've been painted. Is it a big job to bury/ disguise them while
major wrecking is going on anyway?
It could well make a difference. However, I confused what this 22mm pipe is.
I've only come across 20mm and 25mm MDPE. They are approximately equivalent
to 15mm and 22mm copper, as the dimensions are for the outside diameter. The
plastic pipe is much thicker walled than the copper.
Some combis have a pressure reducing valve, which you take the cold through
in order to get pressure balanced supplies. These are good for mixer taps
and showers. However, they might reduce flow rate slightly, so I'd 'T' off
the garden tap and kitchen sink before any such valve, much as you might for
a water softener.
The guy from Waterline said the new pipe from the water main to the property
boundary would be 22mm. He also said it would be new blue plastic pipe?!
Maybe it was just a slip on his part?
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