A diagram of the whole gas pipe system with the meter, fittings, pipe types, lengths, and appliance demands is required.
Once you have that diagram, here's how you check if it complies:
1) A segment is all the piping between two nodes, where the nodes are the meter, the appliances and the tees (edit for the record: and change of size/material fittings). Label each segment with the total flow if all the appliances were running. Also label with the equivalent length, which is the sum of the actual straight pipe segment lengths and the equivalent lengths of the fittings in the segment. For a tee, there are different equivalent length for the straight through path and the 90 degree path; assign each equivalent length to the downstream segment.
2) For each segment, based on pipe type, size, and flow, look up the allowable length (you might need to interpolate if you have the type of table that gives you minimum pipe size for a given length). Divide the actual segment length by the allowable length. That's the fraction of the pressure drop budget that is used by that segment. Label the segment (if you like, you can turn it into a percentage).
3) Now for each appliance, add up the fractions on the path of segments that goes from the meter to the appliance. If the sum is not more than 1 (or 100%), then the appliance will have enough pressure. If all the appliances pass, you're good to go. If some sum exceeds 1, upsize a pipe segment as required, and check again.
Note that in step two, if you have something like a short segment of 1/2" CSST with a high flow, and the wrong sort of table, it may be hard to interpolate E.g. if the table says for 10' you can use 1/2" and for 20' you need 3/4", you really want to know if the transition point is 11' or 19'. So you'll either need the right type of table, or to use a formula for pressure drop and divide that by the allowable pressure drop (for a typical 7" w.c. system, the allowable pressure drop is 0.5" w.c., which is a pretty stringent standard).
Cheers, Wayne
