Desired Outcome:
Sufficient combustion air from the exterior of the home so that fuel burning appliances in the CAZ have adequate air to permit complete combustion.
SWS Detail: 5.0502.1 Combustion Air-Fuel-Fired Appliances
Author: Jesse
Before
CAZ without combustion air
After
CAZ with combustion air
Steps
- 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 test to verify Category I, II and III appliances are venting safely before leaving home for the day.
Testing shall be recorded on the Utah WAP Worst Case Draft Test form.
6. Client Ed
Educate the client on purpose of combustion air opening.
Warn client not to block or plug the opening