Plastic and copper pipe sizing

[malx42]

I am going to replace hot and cold 15mm copper pipe with a plastic system. The hot water is from a combi boiler and the cold water pipe is at mains pressure. The pipe lengths are about 10m each. Looking at the internal bore of 15mm plastic pipe, it’s much smaller than 15mm copper. To ensure sensible flow rates should the replacement plastic pipe be 22mm, or will 15mm plastic pipe, under mains pressure allow sufficient flow?

Many thanks

 

[Scott_D]

How many lpm do you get at the moment

 

[ShaunCorbs]

Why are you replacing the times ?

 

[malx42]

Hi Scott,

Don’t know at the moment, but the feeds have to supply kitchen and 2 bathrooms and a big bath ... and a combi boiler. I think you might have answered the question!

 

[malx42]

Why are you replacing the times ?

The pipes are being re routed, to by pass underfloor pipes where there is a leak.

 

[rpm]

Not my area, however did I read somewhere about plastic being used after a certain distance from a boiler.

 

[SimonG]

Or could just fit 15mm copper.

 

[malx42]

Hi Scott,

Don’t know at the moment, but the feeds have to supply kitchen and 2 bathrooms and a big bath . and a combi boiler. I think you might have answered the question!

Measured it today, it’s 12 litres a minute at the kitchen tap on full bore. Upstairs on the bath tap it’s at 15 lpm . I think the lower value on the kitchen tap is down to a flexible hose tap connector.

Sticking in an extra 20 m of narrow bore 15 mm plastic is going to do no good.

I have been reading about the flow resistance of pipe of different bores. 1m of 15mm has the same flow resistance as 7m of 22mm. I have a lot of 22 mm copper and I think I might use on the cold water side to keep the pressure up to make sure flow rate is not restricted, by the extra pipe length.