Mechanical Code Amendments Offer Clarity on Flue Venting

On December 12, 2025, Metro Codes Mechanical Inspection Chief Alan Fort issued the following notice to contractors registered in Davidson County.

Many Category II and Category IV appliance manufacturers allow the use of PVC and CPVC, but those products have only been tested and listed to plumbing standards, not venting standards. Venting flue gases is a life safety concern and due to the liability of the AHJ the following amendments have been adopted by the Metro Department of Codes and Building Safety:

UL 1738 is the US venting standard that has requirements for the material used and the way it is installed when venting gas appliances. The following amendments will be enforced as of 7/15/2025 with a grace period of 180 days for larger projects which have been in the design phase. All projects after 1/1/2026 will be required to comply with the following.

Section G2427.4.1 of the 2024 Edition of the International Residential Code for One- and Two-Family Dwellings is hereby amended by deleting Section G2427.4.1 and substituting the following:

G2427.4.1 Plastic Piping. Where plastic piping is used to vent an appliance, the material shall be listed and labeled in accordance with UL 1738.

Section G2427.4.1.1 of the 2024 Edition of the International Residential Code for One- and Two-Family Dwellings is hereby amended by deleting Section G2427.4.1.1 and substituting the following:

G2427.4.1.1 Plastic Vent Joints. Plastic pipe venting materials listed and labeled in accordance with UL 1738 shall be installed in accordance with the vent manufacturer's instructions. Where primer is required, it shall be of contrasting color.

Section 503.4.1 of the 2024 Edition of the International Fuel Gas Code is hereby amended by deleting Section 503.4.1 and substituting the following:

503.4.1 Plastic Piping. Where plastic piping is used to vent an appliance, the material shall be listed and labeled in accordance with UL 1738.

Section 503.4.1.1 of the 2024 Edition of the International Fuel Gas Code is hereby amended by deleting Section 503.4.1.1 and substituting the following:

503.4.1.1 Plastic Vent Joints. Plastic pipe venting materials listed and labeled in accordance with UL 1738 shall be installed in accordance with the vent manufacturer's instructions. Where primer is required, it shall be of contrasting color.

For more information regarding these standards, contact Metro Codes Mechanical Inspection Chief Alan Fort at [email protected].