Surely a bottle neck is a bottle neck?

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?
TIA Suzanne
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Suz wrote:

It would increase the flow, but only slightly. The reason for this is friction with the walls. The smaller the bore, the higher the flow velocity, and the greater the frictional loss.
--
Grunff


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Grunff wrote:

..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.
Chris
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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 a minute.
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 installation practices!
Nick
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litres
Any idea what this will reduce to during the winter?
Geoff
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Not expecting the cold flow rate to reduce in winter - the hot rate I also think will 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 temp will only drop by another 5 or 8 degrees and then I guess the boiler will be at about full output. I like my shower at about 37 deg C (Cool) which helps flow rates. Nick

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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. Suzanne
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 different makes.
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?
TIA again Suzanne
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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.
Christian.
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is.
equivalent
The
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? Suzanne
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