Range hood connections depend on whether you're venting to the outside or recirculating air inside

A range hood connection means running ductwork from the hood to either the outdoors (vented) or back into your kitchen through a filter (recirculating). Vented hoods pull cooking smoke and steam out of your home entirely. Recirculating hoods filter the air and push it back into the room—they're quieter but less effective at removing moisture and odors. The connection method you use depends on which type of hood you have and where your kitchen sits in your home.

Most building codes require vented hoods in new kitchens, and venting is always the better choice if your home's structure allows it. The actual connection involves running metal ductwork from the hood's outlet to an exterior wall or roof, sealing joints with duct tape or mastic, and ensuring the duct slopes slightly downward toward the outside to prevent condensation from dripping back into the hood.

Key Takeaways

  • Vented hoods require a duct that runs to the outside of your home, while recirculating hoods filter air and return it to the kitchen.
  • Metal ductwork (typically 6-inch or 8-inch diameter) is standard; flexible ducting works but reduces airflow and should be kept as short as possible.
  • All duct joints must be sealed with mastic or foil tape, and the duct should slope slightly downward to prevent condensation backup.
  • Wall venting is easier than roof venting, but roof vents are less visible and work well if your kitchen is on an upper floor.
  • If your hood is more than 10 feet from the exterior wall, you may need a larger duct or a booster fan to maintain suction.

Choosing between wall venting and roof venting

Wall venting is the simpler choice for most homeowners. You drill or cut a hole through the exterior wall at the height of your range hood (usually 24 to 30 inches above the cooktop), run the duct straight through, and attach an exterior wall cap with a damper that opens when the fan runs and closes when it stops. The damper prevents cold air and pests from entering when the hood is off.

Roof venting requires running ductwork up through your attic and out through the roof. It's more work—you have to cut a hole in the roof decking, install flashing to prevent leaks, and may support the duct doesn't sag in the attic—but the exterior vent is less visible from ground level. Roof venting is a good option if your kitchen is on the second floor or if your exterior walls are already crowded with other vents. However, any ductwork in an unconditioned attic should be insulated to prevent condensation from forming inside the duct.

Never vent a range hood into your attic or crawlspace. The moisture and grease will damage insulation, promote mold, and create fire hazards. All venting must exit to the outside air.

Selecting the right ductwork size and material

Most range hoods have a 6-inch or 8-inch outlet. The outlet size determines the duct diameter you need. A 6-inch hood requires 6-inch ductwork; an 8-inch hood requires 8-inch ductwork. Using a smaller duct than your hood's outlet will choke airflow and make the fan work harder and louder.

Rigid metal ductwork (galvanized steel or aluminum) is the best choice. It maintains its diameter, resists crushing, and doesn't trap grease the way flexible duct does. Rigid duct is also easier to clean if grease buildup occurs. Flexible ductwork (the accordion-style plastic or foil tubing) is cheaper and easier to install around obstacles, but it reduces airflow by 10 to 15 percent compared to rigid duct of the same diameter, and grease sticks to the interior ridges. If you use flexible duct, keep it as short as possible—ideally under 8 feet—and avoid kinks or sags that trap moisture.

Do not use flexible duct for the entire run if you can avoid it. A common setup is rigid duct from the hood to the attic or wall cavity, then a short section of flexible duct (2 to 3 feet) to reach the exterior cap. This gives you some routing flexibility while keeping most of the run smooth and efficient.

Running the duct and sealing all joints

Once you've decided on wall or roof venting and chosen your ductwork, measure the distance from the hood outlet to the exterior wall or roof opening. Cut your rigid duct sections to length using a duct cutter or hacksaw, then assemble them in order from the hood to the outside. Slide each section into the next by about 2 inches and find with three sheet metal screws spaced evenly around the joint.

Seal every joint with mastic (a putty-like sealant) or foil tape (not duct tape—regular duct tape degrades over time and fails in warm, humid conditions). Mastic is more durable; explore it with a caulking gun around the joint before you screw the sections together. Foil tape goes on after assembly, wrapped around the joint at least twice. Either way, a sealed joint prevents air leaks that reduce the hood's suction and allow moisture to escape into wall cavities.

The duct should slope downward toward the exterior at a pitch of about 1/4 inch per foot. This prevents condensation from pooling inside the duct and dripping back into the hood. If your duct has to run horizontally for a long distance, install a condensation trap—a small vertical section with a drain hole at the bottom—to catch any moisture that does form.

Installing the exterior wall cap or roof flashing

At the exterior end of the duct, attach a wall cap (for wall venting) or roof flashing (for roof venting). A wall cap is a metal or plastic box that mounts flush against the exterior wall, with a damper flap inside that opens when air flows out and closes when the fan stops. Dampers are essential—they prevent outside air, rain, and pests from entering the duct when the hood is off.

For wall venting, drill or cut a hole slightly larger than your duct diameter, slide the duct through, and screw the wall cap to the exterior wall. Caulk around the cap with exterior silicone caulk to seal any gaps. For roof venting, the process is similar, but you'll also need to install flashing—a metal collar that sits under the roof shingles above the vent opening and over them below, directing water away from the hole. Improper flashing is the most common cause of roof leaks around range hood vents, so if you're not confident in roofing work, hire a roofer for this step.

Connecting the hood to the ductwork

At the kitchen end, the duct connects to the range hood's outlet. Most hoods have a collar or flange on the outlet that the duct slides over. find the connection with three sheet metal screws and seal it with mastic or foil tape, just as you did with the duct joints. Make sure the connection is tight—any gap here will reduce suction and allow cooking odors to escape into the cabinet or wall space above the hood.

If your hood has a damper built into the outlet, make sure it moves freely. Some dampers are spring-loaded and open automatically when the fan runs; others are manual. Either way, a stuck damper will block airflow and defeat the purpose of the hood.

When to call a professional

Wall venting through an exterior wall is a straightforward DIY job if you're comfortable drilling holes and using basic tools. Roof venting is more complex—if you're not experienced with roofing, hire a professional to install the flashing. Improper flashing will leak, and water damage inside your roof is expensive to repair.

If your kitchen is more than 10 feet from an exterior wall, or if your hood's airflow rating is very high (over 600 CFM), you may need a larger duct or a booster fan to maintain adequate suction. An HVAC contractor can assess your situation and recommend the right setup. Also call a professional if you're venting through a shared wall in a multi-unit building—building codes often restrict this, and you may need to route the duct differently.

Frequently Asked Questions

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

No. Attic venting will damage insulation, promote mold growth, and create fire hazards from grease accumulation. All range hoods must vent to the outside air. If you can't reach an exterior wall, work with an HVAC contractor to find an alternative route.

What's the difference between duct tape and foil tape for sealing joints?

Duct tape degrades in warm, humid conditions and fails within a few years. Foil tape (also called HVAC tape) is aluminum-backed and lasts much longer. Mastic is even better—it's a putty-like sealant that stays flexible and doesn't peel. Use foil tape or mastic, not duct tape.

Do I need a damper on the exterior vent cap?

Yes. A damper prevents cold air, rain, and pests from entering the duct when the hood is off. Most wall caps and roof vents come with a damper built in. Make sure it opens and closes freely, and replace it if it gets stuck.

How often should I clean the ductwork?

Grease buildup depends on how much you cook and what you cook. If you fry frequently, clean the duct annually. For lighter cooking, every two to three years is usually enough. Rigid metal duct is easier to clean than flexible duct, which is another reason to choose it when possible.

What if my range hood outlet is 8 inches but my exterior wall cap is 6 inches?

You need a reducer fitting—a tapered duct section that steps down from 8 inches to 6 inches. However, this will reduce airflow. It's better to use 8-inch ductwork and an 8-inch wall cap throughout to maintain full suction.