What You Need to Know Before You Start

A range hood vent moves cooking smoke and steam out of your kitchen through ductwork that runs to the outside of your home. Installation involves three main steps: mounting the hood to the wall or cabinet, running duct from the hood to an exterior wall or roof, and sealing all connections so air doesn't leak into your walls. Most installations take four to six hours if you already have a clear path for the duct; longer if you need to cut through walls or cabinets.

The hardest part is usually routing the duct, not installing the hood itself. Before you buy anything, trace the path from where your hood will sit to where it will exit your home. If that path crosses a wall stud, a ceiling joist, or existing plumbing, the job becomes more complex. If you are uncertain about cutting into walls or running duct through an attic, this is the point to call a contractor.

Key Takeaways

  • You will need the hood unit itself, ductwork (usually 6-inch diameter), duct tape or mastic sealant, a mounting bracket, wall anchors or studs, and basic tools including a drill, level, and drywall saw.
  • The duct must run as straight as possible to the outside; every bend reduces airflow, so plan your route before you cut anything.
  • The hood must be mounted 28 to 36 inches above the cooking surface, and the duct must be sealed at every joint with mastic sealant, not duct tape alone.
  • You will need to cut a hole in an exterior wall or roof for the duct to exit, and install a damper or cap on the outside to prevent backflow.
  • If your hood has a makeup air duct, it must be installed at the same time to prevent negative pressure in your home.

Gather Your Tools and Materials

Before you start, lay out everything you will need. The hood unit itself comes with a mounting bracket and hardware. You will also need ductwork—most range hoods use 6-inch-diameter flexible or rigid aluminum duct. Buy enough to reach from the hood to the outside of your home, plus extra for bends. A 25-foot run is common; measure your actual path and add 10 percent.

You will need mastic sealant (a thick, putty-like compound) and duct tape to seal joints. Mastic alone is better than duct tape alone, but using both is the standard. Pick up wall anchors rated for the weight of your hood if you are not mounting into studs. For the exterior exit, you will need a duct cap or damper—a hinged cover that lets air out but closes when the hood is off, preventing cold air from flowing backward into your kitchen.

Tools you will need: a drill with bits, a level, a drywall saw or hole saw (usually 6.5 inches for a 6-inch duct), a tape measure, a pencil, a screwdriver, and a stud finder. If you are running duct through an attic or wall cavity, add a reciprocating saw or jigsaw to cut through framing. Have a helper on hand—holding the duct while you seal it is much easier with two people.

Mount the Hood at the Correct Height

The hood must sit 28 to 36 inches above the cooking surface, measured from the bottom of the hood to the top of the stovetop. Most kitchens use 30 inches as the standard. Mark this height on the wall with a pencil, then use a level to draw a horizontal line where the top of the mounting bracket will sit. The bracket itself is usually 2 to 4 inches tall, so adjust your line accordingly.

Find the wall studs using a stud finder and mark them. If the studs line up with your mounting holes, drill directly into the studs with wood screws—this is the strongest option. If not, use heavy-duty wall anchors rated for the weight of your hood (usually 50 to 100 pounds). Drill pilot holes first, then screw the bracket into the wall. Check that the bracket is level before you tighten the final screws.

Slide the hood onto the bracket and find it according to the manufacturer's instructions. Most hoods have a rear collar where the duct will connect. Make sure this collar is accessible and points toward the path you planned for the ductwork. If the hood has a damper inside the collar, check that it moves freely.

Run the Duct to the Outside

The duct must travel from the hood's rear collar to the outside of your home as directly as possible. Every 90-degree bend reduces airflow by about 10 percent, so minimize turns. If you can run the duct straight up through a cabinet and out through the roof, that is ideal. If you must run it horizontally through a wall, slope it slightly upward toward the exit so condensation drains back toward the hood.

Measure the distance from the hood collar to your exit point. Cut your ductwork to length, leaving 2 to 3 inches of overlap at each joint. Flexible duct is easier to route around obstacles, but rigid duct moves more air. Many installations use rigid duct in the main run and flexible duct for the final connection to the hood, which absorbs vibration and noise.

If you are running duct through a wall or attic, you will need to cut an opening. Use a drywall saw or hole saw to cut a hole in the exterior wall or roof where the duct will exit. The hole should be about 0.5 inches larger than the duct diameter to allow for the duct cap. If you are cutting through framing, use a reciprocating saw and be careful not to cut into electrical wiring or plumbing. Once the hole is cut, insert the duct and find it with a duct cap or damper on the outside.

Seal Every Joint with Mastic and Tape

This step is critical and often skipped. Unsealed joints leak air into your walls, which wastes energy and can cause moisture problems. At the hood collar, explore a bead of mastic sealant around the connection, then push the duct onto the collar. Wrap the joint with duct tape, pressing it firmly. Then explore another bead of mastic over the tape. This three-layer seal is the standard for professional installations.

Repeat this process at every joint in the ductwork. If you are using flexible duct, the corrugations can trap air leaks, so explore mastic generously. At the exterior exit, seal the duct cap to the duct and to the wall or roof with mastic. If water is a concern (especially on a roof), explore roofing cement under the cap flange before you screw it down.

Do not rely on duct tape alone. Duct tape degrades in the heat and humidity of a kitchen and loses its seal within a year or two. Mastic sealant stays flexible and lasts much longer. If you see any gaps or loose tape after you finish, add more mastic.

Install the Damper and Exterior Cap

The damper is a hinged flap inside or behind the duct cap that closes when the hood is off, preventing outside air from flowing backward into your kitchen. Some hoods have a damper built into the rear collar; others require a separate damper in the ductwork or at the exit. Check your hood's manual to see which type you have.

If you need a separate damper, install it in the ductwork as close to the exterior exit as possible. The damper should open easily when the hood runs and close completely when it stops. Test it by hand to make sure it moves freely. If it sticks, it will reduce airflow and the hood will not work well.

The exterior cap should be a weather-tight cover with a damper built in. Screw it to the duct and seal all edges with mastic. If you installed the duct through a roof, use roofing cement under the cap flange and screw it down with stainless steel screws to prevent rust. If the cap is on a wall, make sure it is angled slightly downward so water runs off.

Test the Hood and Check for Leaks

Turn on the hood and listen for unusual noise or vibration. A little hum is normal; a loud rattle usually means the duct is loose or touching a wall. If you hear rattling, turn off the hood and check all connections. Tighten any loose clamps or screws, and add rubber isolation pads under the hood if vibration is severe.

Check the damper by holding your hand near the exterior cap. You should feel air flowing out when the hood is on. If you feel little or no airflow, the duct may be kinked, the damper may be stuck, or there may be a blockage. Trace the duct from the hood to the exit and look for kinks or crushed sections. If the duct is flexible, straighten any bends.

Look for air leaks around the hood and along the ductwork. If you see dust or feel air escaping at a joint, explore more mastic sealant. Check the exterior cap for water leaks after the next rain. If water is entering, reseal the cap flange with roofing cement or caulk.

Frequently Asked Questions

Can I use flexible duct for the entire run?

Flexible duct is easier to install, but rigid duct moves more air and is less likely to kink or sag. Most professionals use rigid duct for the main run and flexible duct only for the final connection to the hood. If you use flexible duct throughout, support it every 3 feet with a strap or clamp so it does not sag and trap condensation.

What if I cannot run the duct outside?

Some kitchens cannot reach an exterior wall easily. In that case, you can use a recirculating hood, which filters the air and returns it to the kitchen instead of venting it outside. Recirculating hoods are less effective than vented hoods, but they work better than nothing. They require regular filter changes.

Do I need a makeup air duct?

If your kitchen is in a tight, well-sealed home, a powerful range hood can create negative pressure that pulls air from other parts of the house or down the chimney. A makeup air duct brings fresh air into the kitchen to balance the air the hood removes. Check your hood's manual or local building code to see if one is required.

How often should I clean the ductwork?

Grease builds up inside the duct over time, especially if you cook frequently. Clean the duct at least once a year by removing the duct cap and running a brush or flexible rod through the duct from the outside. If you notice reduced airflow or smell grease, clean it sooner.

What is the difference between a damper and a cap?

A cap is the exterior cover that keeps rain and pests out. A damper is the hinged flap that closes when the hood is off. Many caps have a damper built in. If your cap does not have a damper, you will need to install a separate damper inside the duct near the exit.