The three ways to vent a range hood
A range hood needs to move cooking smoke and steam somewhere. You have three choices: duct it outside through your roof or wall, duct it to your attic or crawlspace, or recirculate the air back into the kitchen through a filter. Outside venting removes the most moisture and odor. Attic venting is cheaper to install but traps humidity in your home. Recirculating filters the air but does not remove moisture, so it works best in kitchens where you already have good ventilation or where ducting outside is impossible.
Your choice depends on your home's structure, your budget, and how much cooking you do. A household that cooks daily and has an exterior wall near the stove should duct outside. A rental or a kitchen far from an outside wall might use recirculating. Attic venting is rarely the best option because moisture buildup can rot framing and encourage mold, but it exists as a middle ground when outside venting costs too much.
Key Takeaways
- Outside venting through the roof or an exterior wall removes the most smoke and moisture but requires cutting through your home's structure and running ductwork.
- Recirculating hoods filter air and return it to the kitchen, costing less to install but leaving humidity in the room and requiring regular filter changes.
- Attic venting is the cheapest to install but traps moisture inside your home, risking rot and mold in framing and insulation.
- Ductwork diameter, length, and the number of bends all affect how well your hood removes air, so undersized or kinked ducts reduce performance.
- Most building codes require outside venting or recirculating; attic venting is often prohibited in newer homes.
Outside venting through the roof
Roof venting is the most common choice for new kitchens and the most effective. You cut a hole in the roof, run rigid or semi-rigid ductwork from the hood up through the attic, and install a roof cap that lets air out but closes when the fan stops. The cap prevents rain and pests from entering when the hood is off.
The main cost is the roof work. If your kitchen is directly below the attic, the ductwork run is short and the job is straightforward. If the kitchen is far from the roof's peak or if your attic is cramped, the run gets longer and more expensive. Longer ducts need larger diameter pipes and more powerful fans to work well. A run longer than 10 feet should use 7-inch or 8-inch ductwork instead of 6-inch, and you may need to upgrade the hood's fan motor.
Rigid ductwork (metal pipe) is more efficient than flexible ductwork because it has fewer places for air to slow down. Flexible ducts are cheaper and easier to route around obstacles, but they have ridges inside that slow airflow and can sag if not supported properly. If you use flexible duct, support it every 3 feet and avoid kinks.
Outside venting through an exterior wall
Wall venting is faster and cheaper than roof venting if your kitchen has an exterior wall near the stove. You drill or cut a hole through the wall, run ductwork horizontally (or nearly so) to the outside, and install a wall cap. The ductwork run is usually shorter than a roof run, so you can often use 6-inch ductwork and a standard fan.
The hole must be large enough for the ductwork and sealed around the edges with caulk or foam to prevent air leaks and pest entry. If the wall is brick or stone, the job takes longer and costs more. If the wall is wood siding or vinyl, it is straightforward. Make sure the wall cap points slightly downward so rain runs off instead of pooling.
One drawback: a wall cap on the side of your house is visible, and some homeowners find it unsightly. It also sits lower than a roof cap, so heavy rain or snow can block it more easily. If your kitchen is on the north side of the house, the cap may stay wet longer and develop mold on the outside.
Recirculating hoods with filters
A recirculating hood pulls air through a filter and pushes it back into the kitchen. It needs no ductwork and no holes in your home. The filter traps grease and some odor, but it does not remove moisture. After cooking, humidity stays in the room and can condense on windows or walls if your kitchen does not have a separate exhaust fan or good air circulation.
Recirculating hoods work best in kitchens with a window, a separate bathroom exhaust fan, or a range hood that vents outside. They are a practical choice for renters, for kitchens in the middle of the home where outside venting is expensive, and for homes where you cook light meals and do not generate much steam. They are not a good choice for a household that cooks daily or uses the stove for canning or boiling large pots.
The filters need replacement every 3 to 6 months depending on how much you cook. Charcoal filters trap odor and cost $15 to $40 each. Mesh filters trap grease and are washable, so they last longer but need cleaning every month. Some hoods use both types stacked together. Check your hood's manual for the correct filter size and replacement schedule.
Attic venting (and why to avoid it)
Attic venting runs ductwork from the hood into the attic and vents the air there instead of outside. It is the cheapest to install because you do not cut through the roof or an exterior wall. The ductwork is short and the work is straightforward.
The problem is moisture. Cooking steam goes straight into your attic, where it condenses on framing, insulation, and roof sheathing. Over time, this moisture causes wood rot, mold growth, and insulation failure. Your heating and cooling bills rise because wet insulation does not work. Mold spores spread into the living space below. In cold climates, moisture freezes and thaws with the seasons, which accelerates rot.
Most building codes written in the last 20 years prohibit attic venting for range hoods. Some older codes allow it, but even where it is legal, it is a false economy. The cost of replacing rotted framing and insulation far exceeds the cost of venting outside. If your hood currently vents to the attic, plan to reroute it outside or switch to a recirculating model.
Ductwork size and installation details
The diameter of your ductwork matters. A 6-inch duct is standard for most residential hoods and works well for runs under 10 feet. For longer runs, more bends, or a hood rated above 400 CFM (cubic feet per minute), use 7-inch or 8-inch ductwork. Undersized ducts force the fan to work harder, making it louder and less effective.
Every bend in the ductwork slows airflow. A 90-degree elbow reduces airflow more than a 45-degree elbow. If you have a choice, use 45-degree elbows and keep bends to a minimum. Flexible ductwork should be stretched tight, not coiled or kinked. Rigid ductwork should be sealed at every joint with mastic (a sticky sealant) or metal tape, not cloth duct tape, which deteriorates over time.
The hood itself should be mounted as close to the stove as possible, typically 24 to 30 inches above the cooktop. The closer the hood, the more efficiently it captures steam and smoke before they spread into the kitchen. If the hood is too high or too far away, much of what you cook escapes into the room instead of into the duct.
Choosing between venting options for your situation
If your kitchen has an exterior wall within 10 feet of the stove and you own your home, outside venting through the wall is usually the best choice. It is faster and cheaper than roof venting, and it removes moisture and odor completely. If your kitchen is in the center of the home or far from an exterior wall, roof venting is the next choice, even if the ductwork run is longer.
If you rent, live in a condo, or cannot modify your home's structure, a recirculating hood is your practical option. Pair it with a window or a separate exhaust fan to handle moisture. If you cook light meals and do not generate much steam, a recirculating hood performs adequately on its own.
If your hood currently vents to the attic, switching to outside venting or recirculating should be a priority. Attic moisture damage compounds over years and becomes expensive to repair. The cost of rerouting ductwork outside is far less than replacing rotted framing.
Frequently Asked Questions
Can I vent a range hood into the attic?
Technically yes in some older building codes, but it is not recommended. Cooking steam condenses in the attic and causes mold, wood rot, and insulation failure. Most modern codes prohibit it. If your hood currently vents to the attic, plan to reroute it outside or switch to a recirculating model.
How long can ductwork be before it stops working?
A 6-inch duct works well up to about 10 feet. Beyond that, airflow drops noticeably and you should upgrade to 7-inch or 8-inch ductwork or add a more powerful fan. Each 90-degree bend counts as about 5 extra feet of ductwork, so a run with multiple bends needs to be shorter or larger.
Do I need a damper in my ductwork?
A damper is a flap that closes when the fan stops, preventing outside air from flowing back into your kitchen. Most roof caps and wall caps have built-in dampers. If yours does not, a separate damper installed in the ductwork near the hood is a good idea, especially in cold climates where outside air can leak in and cool your home.
What is the difference between rigid and flexible ductwork?
Rigid ductwork (metal pipe) is more efficient because it has smooth interior walls that do not slow airflow. Flexible ductwork is cheaper and easier to route around obstacles, but its ridged interior reduces airflow and it can sag or kink if not properly supported. For best performance, use rigid ductwork where possible and flexible only where you need to bend around obstacles.
How often do I need to clean the ductwork?
Grease builds up inside ductwork over time, especially in the first few feet near the hood. Clean the ductwork every 6 to 12 months if you cook frequently, or every 12 to 24 months if you cook light meals. A professional duct cleaning service can do this, or you can hire a handyperson to disconnect the ductwork and flush it with a shop vacuum.