Where the exhaust vent goes and what you need before starting
A range hood exhaust vent is the ductwork that carries cooking smoke and steam out of your kitchen to the outside air. Most installations run the duct horizontally through an exterior wall, or vertically up through the roof or attic. The path depends on your kitchen layout, where the range hood sits, and whether your home has an attic or crawl space above.
Before you cut into drywall or roof material, you need to know what is behind it. Use a stud finder to locate framing, and if you are venting through the roof, go into the attic first to check for electrical wiring, plumbing, or structural beams. Venting through an exterior wall is usually simpler for single-story homes. Venting through the roof works better when the hood is far from an outside wall, but it requires roof flashing and careful sealing to prevent leaks.
Gather these tools before you begin: a drill with bits, a drywall saw or hole saw (the size matches your duct diameter), a level, a tape measure, caulk and caulking gun, roof flashing kit (if venting through roof), exterior vent cap, flexible or rigid ductwork, duct clamps, and a screwdriver. If you are venting through the roof, you will also need roofing cement and shingles to patch afterward.
Key Takeaways
- Horizontal wall vents are faster and leak less than roof vents, but only work if an exterior wall is close to your range hood location.
- Measure your duct diameter before buying the vent cap and flashing, because standard sizes are 4 inches, 5 inches, and 6 inches.
- Seal every joint with duct tape or mastic sealant, and caulk around the vent opening on the outside to stop air leaks and water entry.
- If venting through the roof, install flashing under the shingles above the opening and over the shingles below it to direct water away from the hole.
- Test the hood after installation by turning it on and feeling for air movement at the exterior vent cap to confirm the duct is not blocked.
Choosing between a wall vent and a roof vent
A wall vent (also called a through-wall vent) exits through the side of your house. This is the easiest route if your kitchen is on an exterior wall and the hood is within 10 feet of that wall. Wall vents need less ductwork, have fewer bends, and are less likely to leak because water runs down, not into, the opening. The vent cap sits flush against the siding, and you caulk around it to seal the gap.
A roof vent exits through the roof, usually when the hood is in the center of the house or far from any exterior wall. Roof vents require more ductwork and more bends, which slows airflow and makes the hood work harder. They also need roof flashing—a metal collar that sits under the shingles above the hole and over the shingles below it—to keep rain out. Roof vents are more prone to leaks if the flashing is installed wrong or if caulk fails over time.
If you have a choice, a wall vent is simpler and more reliable. Choose a roof vent only if the hood location makes a wall vent impractical or if local building codes require it.
Measuring and marking the vent opening
Measure the diameter of your ductwork. Most range hoods use 4-inch, 5-inch, or 6-inch ducts. Check the hood manual or look at the outlet where the duct connects. Write this number down—you need it to buy the right vent cap and hole saw.
For a wall vent, find a spot on the exterior wall that is level with the hood outlet and as close to it as possible. Go outside and mark the center point where you want the hole. Use a level to make sure the vent cap will sit straight. For a roof vent, go into the attic and drill a small pilot hole through the roof at your chosen location, then go outside and mark around it. This pilot hole helps you see exactly where you are cutting.
Before you cut, double-check that there is no wiring, plumbing, or structural member in the way. If you are venting through a wall, use a stud finder to confirm you are not hitting a stud. If you are venting through the roof, look in the attic to see what is directly below the spot. Move your mark if needed to avoid obstacles.
Cutting the opening and installing the duct
For a wall vent, drill a pilot hole at your marked center point, then use a hole saw the same diameter as your duct to cut through the drywall and siding. Start from inside the house and push the saw through to the outside. This gives you better control and a cleaner hole. If the siding is vinyl or aluminum, cut slowly to avoid cracking it. Once the hole is through, insert the duct into the opening from inside.
For a roof vent, use the pilot hole you drilled earlier as your guide. From the attic, use a hole saw to cut through the roof decking. Go back outside and use a reciprocating saw or jigsaw to cut through the shingles and roofing material around the hole. The opening should be slightly larger than the flashing collar so the flashing can slide under the shingles above. Insert the duct from inside the attic, pushing it up through the roof opening.
Connect the duct to the range hood outlet using duct clamps. Tighten the clamps so the connection is snug but not so tight that you crush the duct. If the duct has seams, seal them with duct tape or mastic sealant—this stops air from leaking out and reduces noise.
Sealing the vent opening and installing the exterior cap
For a wall vent, slide the vent cap over the duct from the outside. Most caps have a flange that sits flat against the siding. Caulk around the entire flange with exterior-grade caulk, using a caulking gun. Smooth the caulk with a wet finger so it fills gaps and looks neat. Let the caulk dry per the manufacturer's instructions before running the hood.
For a roof vent, install the flashing collar before you attach the cap. Slide the upper edge of the flashing under the shingles above the hole, then lay it flat over the roof. Nail the upper edge to the roof decking (the nails will be covered by shingles), then nail the sides and lower edge. explore roofing cement under the flashing edges and under the shingles you just lifted. Re-nail the shingles over the upper edge of the flashing so they hold it down. Finally, slide the vent cap over the duct and find it per the cap's instructions.
Caulk around the base of the roof vent cap where it meets the flashing. Use roofing cement or exterior caulk rated for roofs. This seals the gap and prevents water from running down the duct.
Connecting the duct run and testing airflow
If the hood outlet and the exterior vent are not close together, you need to run ductwork between them. Use rigid duct (metal pipe) or flexible duct, depending on your space. Rigid duct is more efficient because it has less friction, but it is harder to fit around obstacles. Flexible duct bends easily but should not have more than two or three bends, and bends should be gentle—sharp kinks slow airflow.
Connect each section of duct with duct clamps and seal the seams with duct tape or mastic sealant. Slope the duct slightly downward toward the exterior vent so any condensation drains out instead of pooling inside the duct. If the duct runs through an unconditioned space like an attic, wrap it with insulation to prevent condensation from forming on the outside of the duct.
Once everything is connected, turn on the range hood and feel for air movement at the exterior vent cap. You should feel a strong breeze coming out. If you feel little or no air, the duct may be kinked, blocked, or have too many bends. Check the entire run and straighten any kinks. If the airflow is still weak, you may need a booster fan installed in the duct.
Common mistakes and how to avoid them
The most common mistake is venting into the attic or crawl space instead of outside. This pushes humid air into spaces where it can cause mold and rot. Always run the duct all the way to an exterior opening. Another mistake is using too many duct bends or bends that are too sharp. Each bend slows airflow, so keep the duct path as straight as possible and use long-radius elbows instead of sharp 90-degree turns.
Forgetting to seal duct seams is another frequent error. Unsealed seams leak air and reduce the hood's ability to pull smoke and steam out of the kitchen. Use duct tape or mastic sealant on every joint. For roof vents, the biggest mistake is poor flashing installation. If the flashing is not under the shingles above the hole, water will run down the duct and into your attic. Take time to lift the shingles and slide the flashing under them properly.
Do not use flexible duct as a permanent installation if you can avoid it. It sags over time, traps grease and moisture, and is harder to clean. Use it only for short runs where rigid duct will not fit. Finally, do not skip caulking. Caulk around the vent cap on the outside stops water and air leaks. Use exterior-grade caulk rated for the material you are sealing—silicone for metal, acrylic latex for wood or vinyl.
Frequently Asked Questions
Can I vent the range hood into the attic instead of outside?
No. Venting into the attic pushes moisture and cooking odors into a space where they cause mold, rot, and structural damage. Range hoods must vent to the outside air through a duct that runs all the way to an exterior wall or roof opening. This is a building code requirement in most places.
What size hole do I need to cut for a 6-inch duct?
Use a 6-inch hole saw to cut the opening. The hole should match the duct diameter so the vent cap flange sits flush against the wall or roof. If you are cutting through thick material like stucco or brick, a hole saw may overheat—drill slowly and let it cool between passes.
How do I know if my duct is kinked or blocked?
Turn on the hood and feel for airflow at the exterior vent cap. If you feel little or no breeze, trace the entire duct run from the hood to the outside opening. Look for sharp bends, crushed sections, or debris blocking the duct. Flexible duct can sag and trap grease—straighten it or replace it with rigid duct if it is sagging.
Do I need to insulate the ductwork?
Insulation is not required but is a good idea if the duct runs through an unconditioned space like an attic or an unheated garage. Insulation prevents condensation from forming on the outside of the duct, which can drip back into the hood or the kitchen. Use duct wrap or pipe insulation rated for the temperature range in your attic.
What should I do if water is leaking around the vent cap?
For a wall vent, the caulk around the flange may have failed. Remove the old caulk, let the area dry, and re-caulk with fresh exterior-grade caulk. For a roof vent, the flashing may not be under the shingles above the hole, or the roofing cement may have dried out. You may need to lift the shingles, check the flashing position, and re-seal with roofing cement.