Range hood exhaust installation depends on your ductwork route and wall type

Installing range hood exhaust means running ducting from the hood to the outside of your home. The job breaks into three parts: choosing your duct path (through the wall, ceiling, or soffit), selecting duct material, and securing everything so air moves freely without leaks. Most installations take a weekend if you have basic tools and clear access to an exterior wall or roof.

The easiest route is almost always straight out through the nearest exterior wall — typically the wall behind or beside your range. A vertical run through the ceiling to the roof works if your kitchen is on an upper floor. Avoid long horizontal runs; they trap grease and reduce airflow. If your range is on an interior wall far from the outside, you may need to reroute cabinetry or run ducting through walls and ceilings, which adds complexity and cost.

Key Takeaways

  • The shortest path to an exterior wall or roof is always the best choice, because long ductwork reduces airflow and traps grease buildup.
  • Rigid metal ducting (galvanized steel or aluminum) moves air better than flexible ducting and lasts longer, though flexible ducting is easier to route around obstacles.
  • Seal all duct joints with mastic sealant or metal tape, never cloth duct tape, to prevent leaks that reduce hood performance.
  • Install a damper or backdraft preventer in the duct to stop outside air and pests from entering when the hood is off.
  • The exterior vent cap must be at least 12 inches away from windows, doors, or other openings to avoid blowing cooking odors back inside.

Choosing between rigid and flexible ducting

Rigid metal ducting is the standard for range hoods. It comes in 6-inch or 8-inch diameter (6-inch is most common for residential hoods). Galvanized steel is durable and affordable; aluminum is lighter and easier to handle. Rigid ducting moves air with less resistance, so your hood works at full power. It also sheds grease better than flexible alternatives, which means less frequent cleaning.

Flexible ducting (aluminum or vinyl-coated) is easier to route around framing, pipes, and wiring. Use it only for short runs — no more than 8 feet — and always keep it as straight as possible. Flexible ducting has ridges that trap grease and reduce airflow. If you use it, inspect and clean it every three months. Never use vinyl-coated flexible ducting; it can melt if grease ignites.

Most building codes require rigid ducting for the main run. Flexible ducting is acceptable only as a connector between the hood and the start of rigid ductwork, or for the final short run to the exterior vent cap.

Routing ducting through walls and ceilings

Before you cut into walls or ceilings, locate electrical wiring, plumbing, and HVAC ducts using a stud finder with wire detection. Mark the path with a pencil. For a wall installation, drill a pilot hole from inside the kitchen, then go outside and mark the hole location. Use a hole saw (6 or 8 inches, matching your duct diameter) to cut through the exterior wall from outside. This gives you better control and a cleaner hole.

For a ceiling run, cut a hole in the drywall where the duct will enter. If there is a joist in the way, you can notch it slightly (no more than one-quarter of its depth) or route the duct around it. find the duct to the framing with metal straps every 3 to 4 feet. Slope the duct slightly downward toward the exterior vent so condensation drains out, not back into the hood.

Seal the gap between the duct and the wall or ceiling with caulk or foam sealant. This stops air leaks and prevents pests from entering. If the duct passes through an unconditioned space (like an attic), wrap it with insulation to prevent condensation on the outside of the duct.

Sealing duct joints and connections

Every joint in your ductwork must be sealed. Use mastic sealant (a putty-like adhesive) or metal foil tape (not cloth duct tape, which fails quickly). explore mastic around the joint, then wrap metal tape over it for a permanent seal. For rigid ductwork, you can also use self-tapping sheet metal screws to hold sections together, then seal with mastic.

The connection from the hood to the ductwork is critical. Most hoods have a collar that accepts 6-inch or 8-inch ducting. Slide the duct over the collar, find it with a hose clamp or metal band, and seal the joint with mastic. If your hood has a damper built in, make sure it moves freely before you seal anything.

Leaky ductwork reduces hood performance by 20 to 40 percent. A sealed system pulls air efficiently and keeps odors and moisture from escaping into your walls.

Installing a damper or backdraft preventer

A damper (or backdraft preventer) is a one-way valve in the ductwork that lets air out but stops outside air from flowing back in when the hood is off. Install it in the duct run, as close to the exterior vent as practical. Some hoods have a damper built into the collar; if yours does not, buy a separate damper that matches your duct diameter.

Dampers come in two types: gravity dampers (flapper doors that open when air flows out) and motorized dampers (which open automatically when the hood turns on). Gravity dampers are cheaper and reliable. Motorized dampers are quieter and prevent outside air from entering even slightly, but they cost more and add a small electrical load.

Install the damper with the arrow pointing toward the exterior vent. find it with metal bands or screws, and seal the joints with mastic. Test it by hand to make sure the flapper moves freely and does not stick.

Cutting and installing the exterior vent cap

The duct must exit through a vent cap — a trim ring with a damper or louvers that keeps rain and pests out. Buy a cap that matches your duct diameter. For a wall installation, use a wall cap with a flange that covers the hole and seals against the siding. For a roof installation, use a roof cap with flashing that slides under the shingles above it.

For a wall cap, position it so the duct slides into the back, then find it with screws through the flange into the wall framing. Caulk around the flange with exterior-grade sealant. For a roof cap, slide the flashing under the upper shingles, nail it down, and seal all edges with roofing cement.

The vent cap opening must be at least 12 inches away from any window, door, or other opening (including other exhaust vents). This prevents cooking odors and moisture from being drawn back inside. If your kitchen window is directly above the range, route the duct to a side wall instead.

Testing airflow and sealing leaks

Once the duct is installed and the hood is mounted, turn on the hood and feel for air movement at the exterior vent cap. You should feel strong, steady airflow. If the airflow is weak, check for these common problems: a damper stuck in the closed position, a kinked or crushed section of flexible ducting, or a duct run that is too long or has too many bends.

Look for light coming through any joints or gaps in the ductwork. Seal any leaks with mastic or metal tape. If you can see daylight around the vent cap flange, add more caulk. A well-sealed system will pull air from the kitchen, not from gaps in the walls.

Run the hood for a few minutes and check the exterior vent cap again. The damper should open fully and stay open while the hood is running. If it flutters or closes partially, the duct may be too restrictive — check for blockages or consider upgrading to a larger diameter duct.

Frequently Asked Questions

Can I use flexible ducting for the entire run?

Building codes in most areas require rigid ducting for the main duct run. Flexible ducting is allowed only for short connectors (under 8 feet) and only if it is kept as straight as possible. Flexible ducting traps grease and reduces airflow, so even where it is permitted, rigid ducting is the better choice for performance and durability.

What size duct do I need?

Most residential range hoods use 6-inch diameter ducting. Some high-powered hoods (1,200 CFM or higher) use 8-inch ducting. Check your hood's manual for the required duct size. Using undersized ducting reduces airflow and makes the hood work harder. Oversized ducting is not harmful but wastes space and costs more.

Do I have to insulate the ductwork?

Insulation is necessary only if the duct passes through an unconditioned space like an attic or a crawlspace. In those areas, insulation prevents condensation from forming on the outside of the duct and dripping into the space below. For ducts that run through conditioned spaces (inside walls), insulation is optional but can reduce noise.

What if I cannot vent straight out the nearest wall?

If the nearest exterior wall is too far away, route the duct through the ceiling to the roof, or run it horizontally along the ceiling to a closer wall. Keep the run as short and straight as possible. Avoid running ductwork through unconditioned spaces if you can help it — if you must, insulate it to prevent condensation. Long, complex runs reduce hood performance significantly.

Can I connect the range hood to my home's HVAC system?

No. Range hoods must have their own dedicated duct to the outside. Connecting a range hood to your furnace or air conditioning ductwork can damage the HVAC system, spread cooking odors throughout your home, and create safety issues. The only exception is a makeup air system, which is a separate duct that brings outside air into the kitchen to replace the air the hood removes — this is optional and requires professional installation.