Gas pipe sizing

[fiddler]

I've got a situation where a builder is installing an iron csst hybrid system. When I did the calculations based on the examples in the book I came up with him needing 1-1/4" to his first T then being able to drop down to 1". He came back with a proposed change to using all csst with a mfgr's chart showing 3/4" would work for his layout. Where I am getting confused and suspicious is the allowable pressure drop. How do I determine that he is using the correct pressure drop.

 

[north star]

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"How do I determine that he is using the correct pressure drop."

Have the contractor submit everything in writing , then contact thelocal gas supplier to approve it / check it........Be sure to get their

approval in writing as well.



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[Daddy-0-]

Natural gas or propane?? He may be using elevated pressure (2psi) for the main 3/4" trunk and then stepping down to standard pressure ( .5" PD @11" WC ) for the appliance branches. At standard pressure you won't get a lot of BTU's out of 3/4" CSST. It must also be bonded at the point of entry with a brass/bronze clamp and cu wire. Need more information for a real answer. (# of appliances with BTU load for each, distance of each branch, manifold or no manifold etc.) BTW...each manufacturer has their own slide chart for sizing their CSST pipe. They will usually give them to inspectors if you contact them directly. Great tool to have b/c the code book is limited in actual btu's. Good luck