For the main gas pipe from points "C" to "F", what type of pipe is specified?

The specification for the main gas pipe from points "C" to "F" is black iron pipe because of its durability and ability to withstand high pressures while safely carrying natural gas. Black iron pipe is a standard material used in gas piping due to its strength and resistance to corrosion when properly maintained.

Other materials like galvanized steel may not be approved for gas service in many areas due to the galvanized coating, which can flake off and cause blockages. Plastic is not typically used for main gas supply lines, as it cannot handle the high temperatures and pressures associated with gas. Copper, while used in some plumbing applications, is not suitable for main gas lines due to its susceptibility to corrosion and potential reactions with natural gas. Thus, black iron pipe is the standard choice for ensuring safe and reliable gas delivery in heating systems.