Gas pipe thickness

[Ambergreen45]

Hi,

I've had a couple of quotes from two Gas safe registered plumbers about changing my old boiler to a combi. I'm a bit confused because one says the pipe needs upgrading from 22mm to 28mm and the other says there is no need because I will only install a 24Kw and I live in a small appartment. Apart from the extra cost, who is more likely to be correct?

I also have a 8Kw gas cooker and a 4kw gas fire that run along the gas pipe. The pipe from the meter to the furthest point, the boiler is about 15m long but if I include all elbows and Tees that could make 18m.

I would greatly appreciate any advice.

Thank you.

 

[St0rmer66]

Without doing the full calculations it'll probably need 28mm for most of it and then perhaps 22mm to the boiler after the branches to the other appliances. A 22mm pipe won't carry enough gas all that way for everything.

 

[Dean744PiN5]

36kw total load is quite big so could well need 28mm for part of it.
Are you sure you will be happy with a 24kw? if you have the flow rate go for at least a 28/30kw as in the winter 24 performance is terrible can even take upto 15mins to fill a bath with a 24kw.

 

[bolshy]

The regulations state that the gas pipe must be sized to provide gas to each appliance with less than 1mb drop between meter and appliance inlet. This is with ALL appliances running at full rate. You will need some 28mm pipework, but without seeing the installation, difficult to say exactly how much. Clearly, it's much better to install a little more 28mm pipe than is needed, than not enough.
I would go with the GS engineer who recommends upgrading the pipework.

 

[MrTherm]

It has been good gas fitting practice for decades (and per IGE recommendations) to slightly oversize pipe diameters (even as much as 20%) to allow for future installs and any supply pressure problems without having to rip out and replace for every further additional appliance. Parallel internal installation pipe runs are taking over!

Calculating "exact" flow limit diameters even though they will suffice is a ridiculous practice, mostly derived from a d.i.y perspective, yet no doubt to save on costs it will continue.

Always go for the oversize when and where possible.