I want to extend a gas pipe, the existing pipe is 15mm but the length of the
new pipe is such that I will need to use 22mm pipe for the extension.

Will it cause a problem if the gas travels through the 15mm pipe first then
into the 22mm pipe via a reducing coupler, or should the whole length be
22mm? The present length of pipe is approx 3m (including adjustment for
bends and elbows), the extended length is approx 12m.

There will only be one appliance served.


Thanks

Pete