Gas pipe size

7 Oct 2006
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United Kingdom
At work yesterday installing a ravenheat csi 85t combi (i was changing the rad valves) the (older) gasfitter could'nt get to the 22mm gas pipe (on the other side of a dwarf wall) but could see it. Now on these boilers you are allowed 3m including bends etc of 15mm gas pipe to the boiler so he connected a 15mm to 22mm reducer to the exsisting gas main (leaving approx 2 feet of 15mm) then proceeded to take 22mm to approx 4 inches away from the boiler. When commisioning all was fine with the gas pressures (inlet pressure 20mb burner pressure 10.5 mb). I would have thought this was wrong(and told him) but he just said as long as the pressures are ok it does'nt matter. What do you guys think of that then :?:
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dodgy do as the book says .. 22 to boiler .. reduce on run up ..
Thats what i thought, he said a lot of installers do this and if readings are correct theres no problem.
approached corgi with similar type problem , they were unsure but said as long as the pressures were right then should be o.k.not ideal but in extreme circumstances.
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It doesn't make any difference where in the run the reduced pipe size is, providing the overall pressure drop is within acceptable limits - i.e. 1 mbar. A metre of 15mm tube has the same resistance to the flow of gas whether it's at the beginning, middle or end of a run. However the beginning of a run is more likely to be shared with other appliances in which case they would also be affected.
if you don't know how to size your pipework yer shouldn't be let loose

I do know how to size pipework, i just thought this practice was wrong :eek: obviously not

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