15mm or 22mm for cold mains?

[eveares]

Just to note my plumber has put all the pipe work in. I am really concerned with the 15mm supplying the feed to the boiler and the cold pipes at the same time and not the size of the hot water out from the boiler.

No loop is in place; what Would be the disadvantages of having a 22x15x15 T junction with the 22mm in from the mains with one 15mm feeding the boiler and the other feeding the cold 15mm pipes?

 

[Agile]

The boiler only has 15mm inlet, the 22mm to the boiler would be limited by the 15mm inlet would it not?

You obviously dont understand how fluids behave when flowing through pipes!

You wrongly think that the flow is determined by the smallest pipe in the system.

Suppose I suggest to you that a fluid flows faster in a small pipe and slower in a large pipe.

The only significance of a smaller pipe is greater resistance.

Tony

 

[eveares]

So if your saying at a equal pressure that smaller pipes will have a higher flow rate, then:

Why do people use larger (25/28mm) pipes for the incoming mains from the street when your saying a smaller pipe would give better flow rate? (as in my case)

Why did my old large 5 bedroom detached house use 22mm for the cold water supplys? (could have all 8 cold taps open with good flow rate to them all)

Why do unvented mains pressure systems use 22mm instead of 15mm when your saying 15mm would give higher flow rate?


Lastly please explain why splitting incoming 22mm to two 15mm's, where one 15mm feeds the boiler and the other 15mm feeds all the cold taps/appliances would reduce the overall flowrate?