What size pipes to a bathroom

Hi,

Replacing the bathroom suite at the weekend with a view to replacing the boiler and converting to a presurised combi system in the future. As a hot water supply is already in the kithen would I just tap into that and cap off the airing cupboard end when i do the upgrade? Reason is that the kithen supply is 15mm and the bath is currently 22mm.

I can see under the bath where this reduces to feed the kitchen.

Im fitting a shower bath mixer valve at the weekend so shall i run 15mm hot and cold? Is a combi grunty enough to need 22mm?

I guess the same applies to the upstairs cold supply but under the bath I can tap into the mains supply to the loft (which will get capped off and removed when I upgrade)

Cheers

It's not a 'grunt' issue.
If you leave 22mm hot pipes in place on a combi system, when the tap is opened, they'll be full of cold water. You'll have to run out all the cold before you see any hot from the combi. (Usually, it's not that much of a problem.)

Cheers. So my bath filling and showering experienc won't be affected if i run in some 15mm.

no