Residential and commercial kitchens use exhaust fans to remove cooking odours, smoke and steam from the kitchen. The fan forces cooking exhaust through ducts that vent outside. Most building codes require commercial exhaust fans to route directly through the roof above the area of the fan. Residential kitchen fans route to the roof between ceiling joists and roof rafters. The diameter of the exhaust duct is determined by the size of the duct flange on the exhaust fan. For this reason, it's best to purchase the fan before you buy the sections of duct or the roof jack.
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Things you need
- Electric jigsaw
- Drywall saw
- Drop light
- Hammer and 16-penny framing nail
- Reciprocating saw with utility blade
- Galvanised roof jack
- Cordless screw gun with screw tip
- Self-tapping duct screws
- Circular galvanised exhaust duct
- Duct tape
- 3/4-inch-wide galvanised duct straps
- Rain cap
Determine the location of the exhaust fan on the kitchen ceiling. Refer to the exhaust fan installation instructions and use a drywall saw to cut an appropriately sized opening in the drywall or plaster ceiling as specified in the instructions.
For an under-cabinet mount, such as a range hood, measure the diameter of the duct flange on top of the unit. Use an electric jigsaw to cut a circular opening 1/2 inch larger in diameter in the bottom shelf of the cabinet. Use a drywall saw to cut a similar-size opening in the drywall or plaster ceiling inside the cabinet. Make sure this hole is in line with the circular cutout in the cabinet shelf.
Use a step ladder or built-in ladder to access the attic area above the ceiling. String a drop light from a stable conduit or plumbing line to provide a work light near the kitchen exhaust fan.
Establish a vertical line from the centre of the duct opening in the ceiling to the underside of the roof sheathing where the hole in the roof for the duct will be. Move the centre point of the hole if necessary to avoid rafters in the attic. Drive a 16-penny nail through the underside of the roof sheeting at this location so the point of the nail can be seen on the roof.
Access the roof and locate the point of the nail. This will be the centre of the hole you cut in the roof for the exhaust duct. Cut a hole for the exhaust duct through the roof and roof sheathing with a reciprocating saw and utility blade. Have a roofing contractor or experienced maintenance person install the appropriate galvanised roof jack directly over the hole.
Return to the attic area above the exhaust fan. Insert the end of a 24-inch length of circular galvanised duct through the ceiling and over the flange on the exhaust fan. This will be the lower duct riser. Use a cordless drill with a screw tip and fasten the duct riser to the flange with self-tapping duct screws.
Connect 24-inch lengths of circular duct together until the duct extends through the roof jack to at least 24 inches above the roof. Wrap each of the joints where the duct pieces connect with duct tape to prevent exhaust air from escaping into the attic area.
Secure the lower and upper duct sections to nearby rafters and ceiling joists with 3/4-inch-wide galvanised duct straps. Wrap each strap around the duct at least one complete wrap and fasten each end of the strap to the rafter or joist with self-tapping screws.
Install a rain cap on the top end of the duct. Have the roofing contractor mastic around the duct where it goes through the roof jack.
Tips and warnings
- Consult with an HVAC inspector before routing an exhaust fan.
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