15mm pipe work on hot water system when fitting combi

[darkart]

Hi all first post so be gentle

I am looking to install the hot water side of my condensing system combi system.

I have been told that the hot water side must be plumbed in from the boiler and around the full system in 15 mm pipework rather than 22mm?

Can some of the wise owls on here explain to me in simpleton terms why this is. I noticed that my old taps to the bath were in 22mm pipe work ?

I have been looking to find a plumbing diagram on the internet for a condensing condensing combi system giving pipe sizes for the water runs but cant find any. Any ideas where i can find one?

Cheers all.

 

[daz1766]

The hot water from your new combi boiler will be at mains pressure, the same as your cold water. For this reason the pipework can be 15mm.

Your old system which i guess was gravity fed from a hot water cylinder and header tank required 22mm pipework simply to increase the flow rate as the pressure depended on the hight of your header tank.