Gas pipe sizing

[rolec]

I was always led to believe that on new installations its always best to run a 22mm gas line all the way up to the boiler, obviously on some boilers such as Isars and Icos's the gas connection on boiler is 15mm so you have to reduce down at some point, but on some relatively new installations I viewed recently the gas line has been in 15mm for a considerable length is this ok if everything works out at the boiler when its being commissioned and tested, where do the the regs stand on this, obviously a wrongly sized pipe will cause problems, but what is allowed, I know with Baxi 105's it states that a 22m pipe must run all the way to the appliance, is this the same on all boilers???

[Whiter]

Gas rate and length of pipe run determine pipe diameter

[Henry]

You cannot say 22mm from meter to boiler, every boiler and especially "A" must have 20Mbar working 17 is a fail

Ist check how much gas the boiler needs then with all the other appliances work out the pipe size.

Today I was in a loft putting 5 metrs of 28mm!! to a 30 KW boiler because the installer put too much 15 + 22 I got £250 for that job

[rusm]

most new modern day forced draught combi boilers require a minimum of 28mm but in some instances i have had to run 35mm dependant on length of run, how many elbows etc. There are lots of factors to consider.