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Plumbing

15mm to 22mm = loss of flow rate?

Anonymous user 23/02/2024 - 2.57 PM

I am building a tap / faucet system for my bathroom. Working off 15mm mains and inside piping, via decent but no great Baxi combi boiler. Objective is to fill the bath as fast as possible. No shower involved. My intent is to build the faucet system from 22mm pipe. But I am concerned that the 22mm pipe is at best pointless / more dear given the rest of the system is 15mm pipe. I know flow rate is different than water pressure, but if the rest of the system runs through 15mm pipe then arrives at my 22mm faucet setup, will it not just flow at the 15mm flow rate? Or can I get greater *flow rate* from 22mm, even though it is fed by 15mm? Read a very complicated physics answer to this. But now I'd like to understand. Fairly urgent as I need to start building soon. Thanks.

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2 Answers

Anonymous user

Save yourself the cost and use 15mm because: - flow rate is improved through 22mm because the bends (and pipework) have a lower frictional resistance so unless it's a very long, bendy run there will be no improvement. - 22mm pipework holds more water so on the hot side you'll have more room temp water to run off before the hot comes through. - With a combi, the higher the flow rate, the less heat can be transferred to the water so even if 22mm made an appreciable difference, you would lose some flow from the cold side to compensate.
Answered18 May 2015
5

Anonymous user

From what you are saying, its not going to make much difference what you do at the tap end, the problem sound like your boiler. All combi boilers have different flow rates of hot water. Some have say around 6-7 lts a minute and some have in excess of 17ltr a min. The only real solution would be to swap the boiler and check the incoming mains pressure to the boiler. Hope that helps
Answered18 May 2015
2