central heating combi boiler

[pickled_magpie]

hi there i have just purchased a central heating kit from Band Q th

usual 7 radiators plus combi boiler valves flue etc . on the boiler it has the gas inlet at 15 mm, i have been told by a la man that it has to be 22 mm to feed the gas i am not doing the gas sid of things but was wondering if this is true to have 22mm does this hav to go all the way back to the meter . any info would be appreciate

-- pickled_magpie

[Paul Barker]

Your fitter will know how to pipe size

-- Paul Barker

[andrewpreece]

The rule of thumb is 22mm pipe to within 1 metre of the combi, then use 15mm to connect up. This is purported to be a practical rule of thumb for the average combi. If you have a really powerful model I expect you might need to go to 28mm. It also depends on the length of gas pipe you are running, there is more to the rule-of-thumb than I have mentioned, in that you can only have up to a certain length of 22mm, and you have to take into account any right-angle copper fittings as subtracting a certain amount from the max allowed length etc. Can't remember what the specifics are, you'll have to google for it or look in the u.k.d-i-y archives. I can tell you my 28kW boiler is fed by 22mm pipe to within a metre of the inlet, that the 22mm pipe is about 20 feet long with 2 right angle joints ( gentle curves don't count ) and ISTR that that was within the allowed rule, and the pressure at the boiler measured OK when operational, so that was a good reality check. DYOR.

Andy.

[John Rumm]

Chapter and verse here:-

long with 2 right angle joints ( gentle curves don't count ) and ISTR that Depends on whay you mean by gentle... a "swept" bend does count, just less than an elbow (i.e. adds 0.3m rather than 0.5m to the effective length of the pipe for the purposes of calculation)

[Ed Sirett]

See the Gas Fitting FAQ.