What You Need to Know Before You Start

A range hood vent carries cooking smoke and steam out of your kitchen through a duct that runs to the outside of your house. The duct can go through an exterior wall, up through the roof, or out through a soffit (the underside of your roof overhang). The route you choose depends on your kitchen layout, your roof pitch, and whether you're working in a single-story or multi-story home. Most installations take a full day and require cutting an opening in your wall or roof, so this is a project where mistakes are expensive—if you're not confident with power tools or working at height, hiring a licensed contractor is the safer choice.

Before you buy materials or rent tools, measure the duct diameter your range hood requires (usually 6 or 8 inches), check your local building codes (some areas require permits for roof penetrations), and decide which exterior route makes the most sense for your space. The duct should run as straight as possible and slope slightly downward toward the outside to prevent moisture from backing up into your kitchen.

Key Takeaways

  • The duct diameter must match your range hood outlet—usually 6 or 8 inches—and should run as straight as possible with a slight downward slope toward the outside.
  • Wall vents are simpler than roof vents because they avoid roof penetration, but roof vents work better in kitchens where a wall route would be very long or blocked by framing.
  • You will need to cut an opening in your exterior wall or roof, install a duct collar or roof flashing to seal the gap, and run rigid or flexible ductwork from the hood to the outside.
  • Most building departments require a permit for roof penetrations, so check your local code before you start cutting.
  • Sealing all duct joints with mastic sealant and metal tape prevents air leaks and moisture from entering your walls or attic.

Choosing Between a Wall Vent and a Roof Vent

A wall vent is the simpler option if your kitchen is on an exterior wall and the duct run is relatively short (under 20 feet). You drill or cut a hole through the wall sheathing and siding, install a wall cap with damper flaps, and run ductwork from the hood to that opening. Wall vents are faster to install, less likely to leak, and easier to maintain because you can access them from ground level.

A roof vent is necessary if your kitchen is far from an exterior wall or if a wall vent would require the duct to run horizontally for a long distance. Roof vents require cutting through roof decking and shingles, installing flashing to seal the opening, and running ductwork upward through your attic. Roof vents are more complex and create a potential leak point if the flashing is not sealed properly, but they work well in kitchens where a wall route is impractical.

If your kitchen is on an interior wall, a soffit vent (venting through the underside of the roof overhang) is sometimes an option, though it requires similar work to a roof vent and is less common. Talk to your contractor or building department about which route is allowed in your area and makes sense for your home's structure.

Tools and Materials You Will Need

For a wall vent installation, gather a drill with a large spade bit or hole saw (sized to your duct diameter plus 1 inch), a reciprocating saw or jigsaw, a stud finder, a level, a tape measure, caulk and a caulk gun, metal ductwork or flexible duct, mastic sealant, metal foil tape, hose clamps, and a wall cap with damper. You may also need a drywall saw if you are cutting through interior walls before reaching the exterior.

For a roof vent installation, add a reciprocating saw or circular saw (to cut roof decking), a pry bar, roofing nails, a hammer, roof flashing sized to your duct diameter, roofing cement or mastic, and replacement shingles that match your roof. You will also need a sturdy ladder or roof access and safety equipment like a harness if your roof is steep.

Rigid metal ductwork is more durable and efficient than flexible duct, but flexible duct is easier to route around obstacles and is acceptable for most installations. Never use vinyl or plastic ductwork—it can melt from heat and is a fire hazard.

Installing a Wall Vent Step by Step

Start by locating the exterior wall where your vent will exit. Use a stud finder to identify the wall framing, then drill a small pilot hole from inside the kitchen through to the outside so you can see exactly where the opening will be. Mark the center of your duct opening on the exterior wall with a pencil.

From outside, use a hole saw or spade bit to cut the initial opening, or use a reciprocating saw to cut a square opening slightly larger than your duct diameter. Smooth any rough edges with sandpaper. Insert the wall cap (the trim ring and damper assembly) from the outside, and find it with the fasteners provided—usually screws or nails. Seal around the cap with exterior caulk to prevent water from entering the wall cavity.

From inside, connect your range hood ductwork to the wall cap opening using rigid metal duct or flexible duct. Seal every joint with mastic sealant (a thick, putty-like adhesive) and reinforce with metal foil tape. Mastic is more effective than tape alone because it fills gaps and hardens to create an airtight seal. find the duct to the wall cap with a hose clamp to prevent it from slipping.

Test the hood by turning it on and checking that air flows out the wall cap and the damper flaps open freely. If you feel air leaking around the duct joints, add more mastic and tape.

Installing a Roof Vent Step by Step

Locate the spot on your roof where the vent will exit by measuring from inside your attic and drilling a pilot hole through the roof decking. This hole marks the center of your vent opening. From the roof, mark a circle around the pilot hole sized to your duct diameter plus 1 inch, then use a reciprocating saw or circular saw to cut through the roof decking and shingles.

Carefully pry back the shingles around the opening (do not remove them if you can avoid it—you will nail them back down). Slide the roof flashing under the shingles on the uphill side and over the shingles on the downhill side, so water runs over the flashing rather than under it. find the flashing with roofing nails around its perimeter, then seal under the shingles and around the flashing with roofing cement or mastic. Nail the shingles back down and seal the nail heads with roofing cement.

From inside the attic, connect your ductwork to the roof collar (the metal ring that protrudes from the flashing). Seal all joints with mastic and metal foil tape. Make sure the duct does not sag or kink, and support it with metal straps every 3 to 4 feet to prevent it from sagging over time and trapping moisture.

Once the duct is connected, go back to the roof and inspect the flashing to make sure it is sitting flat and all seams are sealed. A roof vent that leaks will cause water damage in your attic, so take time to get the flashing right.

Sealing and Insulating Your Ductwork

Every joint in your ductwork—where sections connect, where the duct meets the hood, and where it meets the wall or roof cap—must be sealed to prevent air leaks and moisture from entering your walls or attic. Use mastic sealant (also called duct mastic or duct sealant), which is a thick, sticky compound that hardens as it dries. explore it with a putty knife or caulk gun, covering the entire joint, then wrap the joint with metal foil tape for extra strength.

Do not rely on tape alone—tape can peel off over time, especially in humid kitchens. Mastic is the primary seal, and tape reinforces it. Avoid duct tape (cloth tape with rubber adhesive), which deteriorates in heat and humidity and is not approved for range hood ducts.

If your ductwork runs through an unconditioned space like an attic, wrap it with fiberglass duct insulation to prevent condensation from forming on the outside of the duct. Condensation can drip back into your kitchen or soak into your attic framing, so this step is worth doing even though it adds cost and time.

Common Mistakes to Avoid

The most common mistake is running the duct horizontally for too long without a downward slope. If the duct is level or slopes upward, moisture condenses inside it and drains back into your kitchen or hood. Aim for a slope of at least 1/4 inch per foot toward the outside. If you must run the duct horizontally for a distance, install a condensation trap (a small vertical section with a drain) at the low point to collect and remove moisture.

Another frequent error is using too many duct bends or elbows. Each bend increases resistance to airflow, so the hood has to work harder and may not pull smoke effectively. Keep bends to a minimum and use 45-degree elbows instead of 90-degree ones when possible. Long, kinked flexible ductwork is worse than a few bends in rigid duct.

Failing to seal duct joints properly is also common. Unsealed joints let conditioned air escape from your kitchen in winter and allow humid air to enter your walls. Mastic and tape take extra time, but they prevent expensive water damage and mold later.

Finally, do not forget to check your local building code before you start. Some areas require a permit for roof penetrations, and some have rules about duct diameter, slope, or materials. A permit costs money upfront but protects you if there is ever a problem with your home's sale or insurance claim.

When to Call a Professional

If your roof is steep or high, or if you are not comfortable working at height, hire a contractor to handle the roof vent installation. Falls from roofs are serious, and the cost of a contractor is much less than a hospital bill.

If your ductwork needs to run more than 25 feet, or if it requires many bends and turns, a contractor can design a duct layout that minimizes resistance and ensures your hood works properly. A poorly designed duct system will make your hood noisy and ineffective, and you may end up replacing it.

If you are unsure about your local building code or whether you need a permit, contact your building department or ask a contractor. Some areas have strict rules about vent termination (for example, the vent must be a certain distance from windows or property lines), and violating these rules can result in a fine or an order to remove the vent.

Frequently Asked Questions

Can I vent my range hood into the attic instead of outside?

No. Venting into the attic introduces moisture and cooking odors into your attic, which causes mold, rot, and structural damage. Range hoods must vent to the outside. Some building codes explicitly prohibit attic venting and will not pass an inspection if you do it.

What is the longest duct run I can use?

Most range hoods are rated for a maximum duct run of 25 to 30 feet, measured along the duct path including all bends. Longer runs reduce airflow and make the hood less effective. If your kitchen is far from an exterior wall, a roof vent is usually the better choice than a very long wall vent.

Do I need to insulate the ductwork?

Insulation is not required but is recommended if the duct runs through an unconditioned space like an attic. It prevents condensation from forming on the outside of the duct and dripping back into your kitchen. In a conditioned space (like between interior walls), insulation is optional.

Can I use flexible ductwork instead of rigid?

Yes, flexible ductwork is acceptable and is often easier to install around obstacles. However, rigid ductwork is more durable, resists kinking, and provides better airflow. If you use flexible duct, support it every 3 to 4 feet and avoid sharp bends that restrict airflow.

What should I do if the damper flaps stick or do not open?

Damper flaps can stick if they are clogged with grease or dust. Clean them by removing the wall cap or roof cap and wiping the flaps with a damp cloth. If they still stick after cleaning, the damper may need to be replaced. A stuck damper reduces airflow and allows outside air to enter your kitchen when the hood is off.