Plumbing question.

[Road2Ruin]

Hi chaps,

our house currently runs entirely on mains pressure. We have a 22mm pipe that come into the house, this then is imediately converted to 15mm where it then goes straight upstairs and branches to the combi boiler, the bathroom taps, the ensuite taps and everything downstairs.
If I were to change the pipe to 22mm up to where it then splits into its various directions so that all the 15mm pipes fed of the 22mm would this increase the flow to the outlets or is that going to depend on the existing pressure, which may be to low.

Many thanks

[jagnet]

Yes, potentially the maximum flow rate available would increase assuming there isn't a flow issue to the house. This would be most noticeable when opening more than one outlet at a time. For just a single outlet you probably wouldn't notice the difference unless the route taken is particularly tortuous.

For the hot outlets, depending on the size of the combi boiler and its maximum flow rate, you may find that the boiler is the pinch point and increasing the supply pipe size won't make a difference. Any combi shouldn't have an issue supplying a couple of basin/sink taps at a time, but running a bath whilst a shower's in use elsewhere and then turning on the sink hot tap is going to be a bit of a test.

What's the problem that you're trying to solve? Does part closing the main stopcock make the problem worse? If it doesn't then the issue is likely to be pressure rather than flow.

[Road2Ruin]

The boiler is a monster remeha advanta capable of 17L/min so I doubt that is causing the issue. The main problem is that when someone is using the shower running another tap drops the pressue in the shower (not too much of a problem as it is a thermostatic shower). Ideally as the boiler is capable of supplying a lot of hot water I would like to maximise the flow to it and the other outlets so that turniing on a hot ot cold tap will not cause this (or make it less noticeable). Currently it is an easy fix as only floor boards to take up and a very short run of pipe. Just wondered if it might be worth a punt. Will try the stop cock thing tonight and see what happens.

Thanks

[jagnet]

Sounds as though your existing 15mm pipework is a prime candidate for upgrading then. Unless you have short pipe runs and very good pressure/flow to the house, feeding hot+cold shower outlets, plus a third outlet elsewhere is asking a lot of 15mm pipe and is why unvented cylinders have to be fed from a minimum of 22mm.

Edited by jagnet on Friday 23 September 11:13

[M400 NBL]

When I had to have a new combi boiler fitted, a very good friend of my Ex's friend (trustworthy and turned out he charged me less than he quoted) said I had to have 22mm pipe within a certain distance of the combi boiler. Like yours, mine was 15mm as soon as it entered my maisonette so I had 22mm pipe fitted pretty much right up to the new boiler.

Maybe it will be required to fit 22mm pipe at some point anyway.

[ghamer]

Increasing the inlet will help but combis are not good at coping with multiple outlets running at the same time.Especially if the hot water outlet is in 15mm which they usually are.

[Arthur Jackson]

Road2Ruin said:

The boiler is a monster remeha advanta capable of 17L/min so I doubt that is causing the issue.

Sadly, the point is that 17 litres/min is quite good for a combi, but pretty poor for a hot supply generally. 25 litres a min is recommended as a MINIMUM for unvented systems which are essentially doing a similar job i.e. supplying ALL outlets directly from the incoming main. We only spec combis on houses with ONE bathroom and a downstairs cloaks these days.

[Road2Ruin]

Arthur Jackson said:

adly, the point is that 17 litres/min is quite good for a combi, but pretty poor for a hot supply generally. 25 litres a min is recommended as a MINIMUM for unvented systems which are essentially doing a similar job i.e. supplying ALL outlets directly from the incoming main. We only spec combis on houses with ONE bathroom and a downstairs cloaks these days.

I am quite amazed by that. Unless you have a pumped system you are never going to get 25L/min. Even the 17 I could get from boiler is a lot by the time I add in the cold. A good power shower only uses between 8-10 l/min of mixed water! That would still leave 10l/min of mixed water for other outlets. That's enough for a bath and a sink of water...

[Arthur Jackson]

Road2Ruin said:

I am quite amazed by that. Unless you have a pumped system you are never going to get 25L/min. Even the 17 I could get from boiler is a lot by the time I add in the cold. A good power shower only uses between 8-10 l/min of mixed water! That would still leave 10l/min of mixed water for other outlets. That's enough for a bath and a sink of water...

Most water mains are quite capable of 25litres/min. Sadly a combi boiler isn't so they throttle down enormously. My own hot is easily 25litres/min on one outlet. Obviously it reduces as you open further outlets and you are relying on the main from the road to keep up. You can shower whilst the bath is running and have someone open the kitchen tap though. A dull old vented system could do that too of course, but so many have been ripped out.

[Road2Ruin]

Arthur Jackson said:

Most water mains are quite capable of 25litres/min. Sadly a combi boiler isn't so they throttle down enormously. My own hot is easily 25litres/min on one outlet. Obviously it reduces as you open further outlets and you are relying on the main from the road to keep up. You can shower whilst the bath is running and have someone open the kitchen tap though. A dull old vented system could do that too of course, but so many have been ripped out.

The maximum flow rate through a 15mm pipe is approx 30L/min. However anything above 18L/min causes excesive noise and when approaching 20-22L/min will cause cavitation and potential damage to pipes and fixings, so 25L/min out of one outlet is dangerous unless it's 22mm or above. 22mm pipe has a comfortable flow rate of 36L/min.