32mm incoming mains supply - reduce to 22mm or 15mm

[craig1234]

I have a new 32mm incoming water supply which terminates directly below where my new boiler will be located. My thoughts are that I should reduce from 32mm down to 22mm and then where I tee off for the boiler, I use a reducing tee to provide a 15mm feed for the boiler and another 15mm feed for the rest of the house. Is that the correct way to do it or should I reduce from 32mm straight down to 15mm (pressure is good)?

 

[Madrab]

How many outlets/bathrooms/etc. Why the need to go to 15mm? Keep it all @ 22mm right up to the boiler then drop to 15mm. For the rest of the house, keep it all 22mm right up until it needs to branch, that maximises flow and minimises noise, especially after going to the trouble of putting in a new 32mm mains supply.

 

[JohnD]

Is it a combi boiler?

Do you have a bath?

 

[craig1234]

Thanks both. There are two bathrooms and three toilets. Rightly or wrongly, I've already plumbed the bathrooms/toilets in 15mm but haven't completed the run from the boiler to the first bathroom (the second bathroom tees off from the first) or kitchen. I can therefore run in 22mm up to the boiler, tee off to the boiler in 15mm and then round to the kitchen and first bathroom in 22mm. For the hot water (it will be a combi boiler), is there benefit in doing the same i.e. running in 22mm from the boiler round to the first bathroom and kitchen?

 

[Madrab]

Unfortunately a combi boiler, even the largest one will struggle to supply more than one HW outlet at a time unless there is some well thought out flow restrictors/water savers etc used. 22mm HW from the boiler won't make much difference as the amount of HW delivered at a desired temp is dictated by the output of the boiler so the pipework won't alter that. If there are the chances that more than one HW outlet could be used at a time then that needs to be understood and managed by the occupants. i.e, if someone is in the shower and the other shower or another HW outlet is used then that will directly impact on the showering experience.

When it comes to using 22mm pipework for supplies the design logic in any advance H&C water domestic system is to maximise flow but minimise noise, that is dictated by pipe sizing and loading units. 15mm pipe will happily supply enough flow and pressure as outlets will need but the water velocity needs to increase substantially to do it. When water velocity exceeds ~ 2m/s then it starts to create noise/hammer/friction. All these things aren't desirable in a well thought out/designed system.

 

[craig1234]

Thanks Madrab - very interesting/useful information.
It's only a small/medium sized 3 bedroom house (which will be rented out) so I don't think it's unreasonable for people to stagger their water demand.
I will heed the advice and use 22mm up to the point where it need to split off.