# 1/2 inch gas line for condensing boiler



## gianni (9 Oct 2010)

I was told by an installer that all the new high efficiency gas boilers require a 3/4 inch gas line. But in the same breath he told me 99% of Irish houses have a 1/2 inch feed. Can this be true ?

Does that mean that everyone who wants a high efficiency boiler has to run a new gas line ? 

If anyone has recently upgraded to a high efficiency boiler, I'd like to hear how they got on.

Thanks

-G


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## DGOBS (9 Oct 2010)

The majority of hi-eff condensing boiler require a 3/4 gas pipe due to the nature of how they operate (using zero governor gas valves) 

There are some models that cope with a 1/2 inch line, but have a limited output 
and would not be useful for medium to large installations

The allowed pressure drop across a natural gas line (from the meter to the appliance) is 1 m/bar, ng being normative at 20m/bar this would mean minimum of 19m/bar at the appliance.

Traditional boilers required somewhere in the region of 10-14 m/bar to operate 
correctly, depending on the appliance so if the pipework had been undersized as long as 14m/bar was available the boiler worked fine (even though the pipework was not to standard)

But the new boilers do not work that way, and the 20m/bar is required (with the correct volume of gas) 

In short, a lot of new boilers have been installed on a gas pipe that is undersized, and the boilers are not working correctly, I know as I have shut some of them down!


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## villa 1 (10 Oct 2010)

You would have to ask the question " If you are to replace the old gas boiler with a new condensing model, will I have to replace the old 1/2 inch supply with a new 3/4 inch supply pipe, and does that mean piping a new bigger supply pipe back to the meter?"


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## DGOBS (10 Oct 2010)

The 'hockey stick' off the meter is 3/4 pipe, and usually this will be brought into the house as 3/4 to somewhere close to the boiler (most installers tee or manifold near the boiler, at least the good ones do) so hopefully it wouldn't be a huge long pipe run that would have to be redone, only to the manifold.

That said, I have found some 'idiot' installs where the installer teed down to 1/2 inch right at the meter!


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