Note: If using Trac Pipe use their specifier for sizing. (Located on APR/Citrix Desktop)
This chart will give you the cubic feet of gas required. Use the formula below to get the proper sizing from chart.
Cubic Feet of Gas Required =
Gas Input of Unit (BTU/HR) / 1000 BTU/HR (Heating Value of Natural Gas)
Assume 60,000btu furnace and we have to go 40 feet. Take 60,000 / 1000 = 60 cubic ft of gas required;therefore 1/2 inch pipe will make it (See 63 in red on the chart)