Schedule 40 pipe is used in an LP Gas system with two stage regulator with a length of 70′ and with a pressure drop of 1/2″ water column. What is the minimum size pipe if the piping must carry 80,000BTUH?

Schedule 40 pipe is used in an LP Gas system with two stage regulator with a length of 70′ and with a pressure drop of 1/2″ water column. What is the minimum size pipe if the piping must carry 80,000BTUH?