I am installing a 400,000 BTU water heater for swimming pool. Need to run a natural gas line about 20 ft from my water heater. I'm working with town to get permit and have plumbing make the connection to the water heater after I have installed the line. I'm planning to a simple straight 20' STR11 pipe underground connected to 2 risers to feed the pool heater. No plans to ever extend the line for anything else. I can't get a clear answer from the gas co on what size pipe I need to use. The 1st pipe sizing chart I saw says to use 1-1/4" pipe for natural gas for 20' distance in order to provide 441 BTU. But this is for the table with Gas Pressure of 0.5 psi or Less and a Pressure Drop of 0.5"WC . There are other tables. How do I know what gas pressure and pressure drop is, so I use the right table. I asked the gas company, but they couldn't didn't know how to answer.