I am looking to find any information on how to calculate natural gas supply line size for a recently installed grill. Burners total 100,000BTU. Though I have not checked it, I am told that supply pressure is approx. 7"w.c. The run is about 70ft or so. I presently have a 3/4" supply, which is great for 2 burners and the "pro sear", which totals 58,000 BTU. When I ignite the last 3 burners, there is a noticeable drop in gas supply to the already lit burners. I have called my gas supplier, and they won't give me an answer, rather they told me to ask a plumber. I contacted Sureheat, who manufactures the grill, and they feel that the supply is probably adequate. The unit is warrantied, but if a repair tech comes out and finds the supply inadequate I may be responsible for the service call. Is there some table or calculator used to figure pipe diameter given a certain pressure for a given BTU requirement?