Why hot water copper pipe is 22mm and cold is 15mm?

[JohnMalcolm]

Hi All,
I have this silly question. Water pressure for hot water is a bit low while cold water has a decent pressure.
Why do they put 22mm copper pipes for hot water? It seems detrimental for already low pressure.
Best regards

 

[Last Plumber]

Why do you think it detrimental?
The larger pipe bore reduces pressure loss. If the hot is open vented/tank fed and has low pressure, that is the reason 22mm has been used.

 

[SimonG]

As above, you will find a lot of hot water feeds to baths in 22mm all due to old tank fed hot water. Just like a lot of cold feeds to baths are in 15 as its mains.

 

[adomas]

There is a cold water tank in the loft. And a hot water tank in the airing cupboard. The current pipe work is about 20 years old. The hot 15mm pipe that's currently there feed straight down stairss to a utility sink. The cold 15mm is the direct feed in from the main stop tap.

 

[cjg]

22 mm will give better flow rate, to bath upstairs. 15mm going down will have more pressure due to drop.