Kitchen hood venting sends cooking smoke and steam outdoors through ductwork instead of recirculating it back into your kitchen
A range hood that vents outside removes moisture, heat, and cooking odors at the source rather than filtering and returning them to your home. The duct carries air from the hood to an opening in your exterior wall, roof, or soffit. This is different from a recirculating hood, which filters the air and pushes it back into the kitchen—a vented hood is more effective at removing humidity and smell, but it requires running ductwork through your walls or ceiling.
The basic path is straightforward: hood → duct → damper → exterior wall or roof. What makes the installation real work is routing the duct without kinks, keeping it as short as possible, and choosing the right exit point for your home's structure.
Key Takeaways
- Vented hoods require rigid or semi-rigid ductwork that runs from the hood to an opening on your exterior wall, roof, or soffit—flexible dryer-vent-style duct should not be used for range hoods.
- The shortest, straightest duct run is best; every bend and every foot of length reduces airflow, so a direct path through an exterior wall is more efficient than routing through the attic to the roof.
- A damper (a one-way flap) prevents outside air from flowing back into your kitchen when the hood is off, and it should be installed in the duct between the hood and the exterior opening.
- Roof vents work but collect grease and require regular cleaning; wall vents are easier to maintain and less likely to leak, but you need an unobstructed exterior wall.
- If your hood is more than 10 feet from the nearest exterior wall or roof, or if your ductwork requires more than two 90-degree bends, the hood may not move air effectively and a professional assessment is worth the cost.
Choosing between wall, roof, and soffit vents
A wall vent is the most common and practical choice. You cut a hole through the exterior wall (usually 6 or 8 inches in diameter, depending on your hood) and install a dampered vent cap on the outside. The duct runs horizontally or slightly downward from the hood to that opening. Wall vents are straightforward to clean, less likely to leak, and keep the duct run short if your kitchen is on an exterior wall.
A roof vent requires running ductwork up through your attic or ceiling cavity and out through the roof. Roof vents collect grease and condensation more readily than wall vents, and they are harder to clean without getting on the roof. They also create a potential leak point where the vent penetrates the roof. Use a roof vent only if your kitchen has no suitable exterior wall, or if your hood is on an interior island and a wall vent would require an impractically long duct run.
A soffit vent (the underside of your roof overhang) is tempting because it looks less visible, but it is a poor choice for range hoods. Soffit vents are designed to bring fresh air into your attic, and a range hood vent can push grease and moisture into that space, damaging insulation and attracting pests. Avoid soffit vents unless you have no other option.
Duct material and sizing
Use rigid metal ductwork (galvanized steel or aluminum) or semi-rigid metal duct for a range hood. Do not use flexible plastic or foil dryer-vent-style duct. Flexible duct traps grease, collapses under negative pressure, and is a fire hazard in a kitchen. Rigid duct is smoother, moves air more efficiently, and is easier to clean.
Most residential range hoods use 6-inch or 8-inch diameter ductwork. Check your hood's manual or the outlet collar on the hood itself to see what size it requires. The duct diameter should match the hood outlet—do not step down to a smaller duct, as this will reduce airflow and trap grease.
Ductwork should slope slightly downward as it runs toward the exterior (about 1/4 inch per foot). This helps condensation drain back toward the hood rather than pooling in the duct. If your duct must run upward to reach a roof vent, install a condensate trap (a small U-shaped section of duct) at the lowest point to catch water.
Installing the damper and exterior vent cap
A damper is a one-way flap that lets air out but prevents outside air, pests, and cold from flowing back into your kitchen when the hood is off. Install it in the duct between the hood and the exterior opening, as close to the hood as practical. Some dampers are built into the vent cap on the outside; others are separate inline dampers installed inside the duct. Check your hood manual to see if a damper is included or required.
The exterior vent cap is the visible part on your wall or roof. It should have a damper flap, a screen to keep pests out, and a trim ring or flange to seal the gap between the duct and the wall or roof. Install it so the flange sits flush against the exterior surface, then caulk around the flange with exterior-grade silicone caulk to prevent water from seeping in. On a roof vent, use roofing cement under the flange and seal all edges.
Routing ductwork through walls and ceilings
The path from hood to exterior should be as direct as possible. Every bend slows airflow and traps grease. If you must make turns, use 90-degree elbows rather than flexible duct, and limit yourself to two bends maximum. A duct run longer than 10 feet or with more than two bends will lose significant airflow; if your kitchen layout requires this, you may need a more powerful hood or a professional assessment.
When running duct through a wall cavity, use a wall thimble (a metal sleeve) to protect the duct from insulation and to provide a clean opening for the vent cap. Drill or cut the hole from inside the kitchen first, then measure and cut from outside to may support the opening is the right size. Seal any gaps between the duct and the wall framing with caulk or foam sealant to prevent air leaks.
If your duct must run through an attic to reach a roof vent, keep it away from insulation and may support there is clearance around it. Do not let the duct touch rafters or electrical wiring. find the duct with metal straps every 3 to 4 feet to prevent sagging.
Connecting the hood to the ductwork
Most range hoods have a collar or outlet on the top or back where the duct connects. Slide the duct over this collar and find it with a stainless-steel hose clamp or duct tape rated for high temperature (aluminum foil tape, not standard duct tape). Make sure the connection is airtight; any leak will reduce airflow and allow cooking odors to escape into your walls.
If your hood has a damper built into the outlet, make sure it moves freely before you seal the connection. Some hoods also have a grease trap or baffle filter that you will need to clean regularly—check the manual for the maintenance schedule.
When to call a professional
If your kitchen is on an interior wall with no direct path to the exterior, if your duct run would be longer than 15 feet, or if you are unsure about cutting through exterior walls or the roof, hire a licensed HVAC contractor or a kitchen remodeler. They can assess your home's structure, recommend the best vent location, and handle the cutting and sealing work correctly. A poorly sealed duct opening or roof penetration can lead to water damage or air leaks that cost far more to fix later.
If you are uncomfortable working at heights or on a roof, a professional should install the exterior vent cap and seal it properly. This is one of the most common sources of leaks in vented hoods.
Frequently Asked Questions
Can I use flexible duct for my range hood?
No. Flexible duct traps grease, restricts airflow, and is a fire hazard. Use rigid or semi-rigid metal ductwork only. Flexible duct is acceptable for dryer vents but not for range hoods.
What size duct do I need?
Check your hood's manual or the outlet collar on the hood itself. Most residential hoods use 6-inch or 8-inch ductwork. The duct diameter must match the hood outlet to avoid losing airflow.
Is a roof vent or wall vent better?
A wall vent is usually better. It is easier to clean, less likely to leak, and keeps the duct run short. Use a roof vent only if your kitchen has no suitable exterior wall or if a wall vent would require an impractically long duct run.
Do I need a damper?
Yes. A damper prevents outside air, pests, and cold from flowing back into your kitchen when the hood is off. It should be installed in the duct between the hood and the exterior opening, or built into the vent cap.
How often should I clean the ductwork?
Clean or inspect the duct and vent cap every three to six months if you cook frequently, or annually if you cook less often. Grease buildup reduces airflow and is a fire hazard. Use a duct brush or hire a professional duct cleaning service if the duct is long or hard to reach.