replacing 15mm with 22mm. Is it worth it?

[deanomc]

I have a 25mm cold water mains coming into my house under the sink downstairs. Then a 15mm stopcock followed by a 15mm pipe going to a Valliant 35w combi boiler. On the way to the boiler this pipe T’s off to the downstairs sink, dishwasher, then upstairs to the toilet, basin, bath and then finally the thermostatic shower valves before feeding the boiler. A 15mm hot pipe then comes from the boiler and T’s off with 15mm pipes to the thermostatic shower vale, bath, basin, then lastly the downstairs sink. I am renovating the whole house so my question is this. Should I replace the 15mm pipe feeding my boiler with a 22mm with 15mm T’ing off to the appliances? And is it also worth replace the 15mm hot pipe coming from the boiler with a 22mm with 15mm Ting off to the appliances? I can draw a diagram if my explanation is not enough. I am also thinking of adding a three zone underfloor heating at a later date.

 

[JCSPLUMBING]

No. Your combi can only produce about 13 litres a min hot water flow. 15mm pipe is more than adequate. In fact I generally remove 22mm bath pipes when changing the vented system with a combi as you get better performance and hot water response. As long as your mains pressure and flow rate meet the manufacturing instructions then your good to go

 

[Meady]

I would change the 15mm to 2mm going to the boiler as it is feeding everything else. But 15mm off the boiler is fine.

 

[rocketmanbkk]

Usually pipe runs are in 22mm reducing to 15mm where needed.

 

[deanomc]

If I had a 22mm feeding the boiler with T's coming off at appliances such as the shower and basins would it be difficult to balance the thermostatic shower as the hot will all be 15mm and therefore different flow rates? Or doesn't this matter in a combi system?