Size Of water supply pipes to bath with Combi

[whodareswins]

I am currently replacing an old bath room suite - the hot water supply is from a Vaillant Combi ( recently installed ) and hot water supply pipe is 15mm - the existing bath has both hot and cold supplied by 15mm pipe - would the hot water tap/and or cold be better served by 22mm pipe or doesn't it matter with a combi?

Also, can I extend the pipes serving the bath to also supply an over bath shower which is Combi Compatible? If 22mm pipe is better for supply to bath should is then be reduced to 15mm to supply shower?

Vi appreciated please

 

[kevplumb]

just use 15

 

[corgiman]

the small the bore the higher the pressure, as kev says stick to 15mm

 

[whodareswins]

Thanks very much Kevplumb and Corgiman - 15mm it is then, nice and simple!