1. Determine duct size

• Follow work order and IRC G2407.6 or IFGC 304.6 to determine appropriate combustion air duct sizing.

2. Determine duct route

• Determine most direct route to run combustion air opening.

• Combustion air openings shall communicate directly, or by ducts, with the outdoors or spaces that freely communicate with the outdoors.

3. Cut hole for termination

• Follow steps 3a-3k to cut exterior hole for termination.

3a. Unobstructed termination

• Ducts shall terminate in an unobstructed space allowing for free movement of combustion air to the appliance.

3b. Mark hole interior

• Mark hole from interior of home.

• Take care to avoid structural members and electrical and plumbing lines.

3c. Drill pilot holes

• Where exterior cladding permits, drill pilot holes from interior of home to indicate where the edges of the hole will be.

3d. Mark hole exterior

• Use the pilot holes as a reference and mark the location of the hole on the exterior of the home.

3e. Cut hole

• Determine duct size and cut hole in exterior wall slightly larger, but not more than 1/4" larger.

• Take care not to cut any plumbing or electrical lines.

3f. Drill hole

• If installing termination through masonry or stone, use a core drill to cut hole.

3g. Install flashing

• Whenever possible, install flashing under cladding.

3h. Install termination

• Position Termination and orient with louvers in a downward position to prevent precipitation from entering the home.

• Secure to house using 4 or more exterior grade fasteners.

3i. Seal termination

• Seal gap between termination and exterior of home with exterior grade caulk to prevent water intrusion.

3j. Louvers and Grilles

• Louvers and grilles shall be fixed in an open position.

• Grille and screen openings cannot be smaller than 1/4".

• Ducts shall not be screened where terminating in an attic space.

3k. Pest screen

• Vent termination shall have screen material with no less than 1/4" and no greater than 1/2" hole size in any direction to prevent pest entry.

4. Install duct

• Follow steps 4a-4e to install duct.

4a. Ducts must be galvanized steel

• Ducts shall be constructed of galvanized steel complying with chapter 6 of the IMC code or material having equivalent corrosion resistance, strength and rigidity.

• Flexible duct shall not be used for combustion air.

4b. Assemble duct

• Cut and assemble duct.

4c. Install fasteners

• Install fasteners per code to hold duct together and to connect to termination collar.

4d. Seal with mastic

• Seal all duct seams and fittings with mastic.

• Follow instructions under Air Seal Duct to seal the duct.

4e. Insulate the duct

• If any portion of the combustion air duct runs through the unconditioned space, the duct shall be insulated to an R-8 or greater.

• Follow instructions under Duct Insulation to insulate duct.

5. Worst Case Draft test

• Conduct a Worst Case Draft (WCD) test to verify Category I, II, and III appliances are venting safely before leaving home for the day.

• Testing shall be recorded using the Utah WAP Worst Case Draft Test form.

6. Client education

• Educate the client on purpose of combustion air opening.

• Warn client not to block or plug the opening.