I am re doing some pipe work in my flat. The cold mains that comes up is 15mm copper, through stopcock and tees off to kitchen sink, the other branch of the 15mm T after a meter upgrades to 22mm copper for its run down to the boiler, and the bathroom. Is this necessary? I want to re route this pipe, and was wondering if I can just do this in 15mm or if that will reduce the flow rate somehow, even though the incoming pipe work is 15mm before changing to 22.
Then there’s the hot! The 15mm pipe coming out of the combi boiler changes up to 22mm after a couple of meters, and supplies bathroom and back to sink. Does this step up to 22mm do anything? The first few meters are 15mm so If I just change all to 15mm will it be ok? Or will the bath take longer to fill due to resistance or anything? I guess they were just using the pipe work from the old tank system, but the cold feed upgrade has me stumped.
Edit* it’s a vaillant condensing combi boiler
Thanks!
Are you a tradesperson and able to answer this question?
Changing your cold feed to the boiler from 22mm to 15mm shouldn’t effect its performance much as a lot of combi boilers and system boilers are made with 15mm connections (I suspect you have one of the two) and I have fitted many with a firm I’ve worked for and have never had any problems with having 15mm pipe running to them but if possible check the manufacturers instructions if you have them as it will say in there if it does need 22mm Depending on distance.
Also changing your hot feed to 15mm will reduce your flow rate a bit but if you have a combi boiler it won’t effect it as much.
Answered2 January 2021
1
Anonymous user
Historically, the hot water came from a tank with a feed and expansion tank in the loft , so the hot water pipe from the HW tank in the airing cupboard was approximately half a bar of pressure. If you have a combi boiler giving you nearly mains pressure of hot water ( mine is three bar, 6x a system boiler) then it really doesn't matter. Keep the 22mm pipe on the hot water. The pressure from a combi boiler is just going to make your shower experience a great experience
If its a combi and mains pressure cold water then 15mil is fine, 22 was for flow rates to your hot water when it was a regular boiler, it mist likely had low pressure cold at 1 time too. Unless your combi is a high flow combi
Hi there,
You could change your cold feed to the boiler to 15mm that would be fine. However I would keep with 22mm to the bathroom particularly the bath because this will increase the flow rate of the water when you want a bath and make it fill at an adequate rate
22mm will increase the flow rate ie baths and basins
All baths and basins are 22mm reduced down to 15mm
Answered2 January 2021
1
Anonymous user
Before a combi boiler was fitted, the system was open vented. With that type of system the hot pipe is always 22mm to provide greater flow than would be possible with 15mm. Now there is a combi the 22mm is not necessary, but changing takes time and costs money. "It won't hurt. Leave it in." is what most installers and, indeed, householders would say.
