gas supply pipe to combi

[bilge]

I have been told that the 15 mm gas supply pipe to my 8 year old Vaillant TurboMax vuw 242E should be 20 mm .

Is this correct?

The installation manual only states a minimum of 15 mm.

tia

[Christian McArdle]

It is more complicated than that and depends on the exact routing and lengths. However, 22mm would be more likely to be required in most circumstances.

Christian.

[logized]

It depends on the maximum gas requirements of all your appliances and the diameter, lengths and bends of all your pipework. There is info on how to calculate it here - (Adobe PDF Document)

is important to get it right because if there is not enough gas pressure available - then an appliance may produce deadly carbon monoxide fumes. I think it is a good idea to upgrade the pipework to 22mm anyway.

Dave

[bilge]

It is important to get it right because if there is not enough gas pressure

thanks for advice and info

[Ed Sirett]

No, it should (almost certainly) be 22mm .

And the minimum is presumably not good enough here. See FAQ.

[John Stumbles]

The rule of thumb is 22mm from the meter most of the way to the boiler, with up to 1 metre of 15mm to the boiler itself if necessary. However thumbs are all different sizes :-)

If the run from the meter to the boiler is very long (over 20 metres) and/or the boiler is very big (over 28kW) some of the pipework may need to be in 28mm. However the maximum permissible lengths for given flow rates depend on something like the 4th power (i.e. squared and squared again) of the pipe size, so 3m of 15mm pipe is equivalent to perhaps

100m or so of 28mm; in other words even a fairly modest length of 15mm will impose an unacceptable pressure drop in the pipework.