Combustion Air–Interior

Desired Outcome:

Install transfer grill at the CAZ boundary to provide sufficient combustion air from the interior of the home so that appliances in the CAZ will have sufficient ventilation to permit complete combustion of the gas.

SWS Detail: 5.0502.1 Combustion Air - Fuel-Fired Appliances

Author: Matt Turner

Before

After

Steps

1. Determine location of interior combustion air opening

Follow work order and IRC G2407.5 or IFGC 304.5 to determine appropriate combustion air duct sizing and location.

2. Outline

Draw outline of hole onto drywall or door.
According to the IFGC, the openings should be within 12 inches of the top and bottom of the CAZ. Two openings are required when providing combustion air from an adjacent interior space.

3. Cut hole

Carefully cut the transfer grill hole.
Support the cutout while cutting to prevent chipping or tearing.

4. Add blocking as needed

If wiring, venting, or plumbing piping are now visible blocking and sealing must be done to separate from the living space.

5. Seal wall cavity

If the wall communicates to the exterior, block and seal the entire wall cavity.

6. Install grilles

Mechanically fasten louvered grills on finished sides of walls and on both sides of doors.

7. 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.

8. Client education

Educate the client on purpose of combustion air opening. Warn client not to block or plug the opening.

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