New Bath, pipe sizes

[LAB]

Hi
replacing a walk in shower with a new bath, house recently had new Boiler, does the bath hot water tap require a 22mm! pipe or will a 15mm do in this day and age, if not, will the "tail" of the 22mm be still connected under the floorboards, (upstairs) only bought the house and have no clue of the plumbing layout.

[plumbbob]

If the hot water supply is at mains pressure because the new boiler is a combi for example then the pipe size could be reduced to 15mm. IF the installation still has header tanks and therefore a low pressure system, or the pipe supplies more than one bathroom then 22mm may be required.

[terryleth]

If the run from your boiler/hot water tank was all in 22mm the water would have an easier time getting to your hot tap, the thinner the pipe - the harder it is for the water to get through it.If you up all the pipework to 22mm you will just end up with 3x the amount of cold water to run through the taps before the hot water reaches it which on a combi-boiler will take a while.