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First determine the effective length of the gas supply line by measuring the actual length of piping, and then adding 5 ft. for every elbow or “T” to the actual length. Use the charts below to determine the pipe diameter necessary to accommodate the BTU demand of the unit. If there are more gas drawing appliances on the line, size according to the maximum amount of BTU demand. FOR NATURAL GAS Maximum Capacity of pipe in Cubic Feet of Gas per Hour Follow boxed numbers for piping just one 125 HX f