Where your range hood vents determines how well it removes cooking smoke and odor

A range hood pulls steam, smoke, and cooking odors from your stovetop and sends them somewhere—either outside your home or back into the kitchen through a filter. The venting route you choose affects how much noise the hood makes, how often you replace filters, and whether cooking smells linger in your house. Most hoods vent to the outside through ductwork that runs through your walls or ceiling. Some recirculate air back into the kitchen after passing it through a charcoal filter. Understanding which type you have and how it works helps you maintain it properly and know when to call a professional.

Key Takeaways

  • Range hoods either vent outside through ductwork or recirculate filtered air back into the kitchen—outside venting removes odors completely, while recirculation traps them in a filter you must replace regularly.
  • Outside venting requires a duct that runs through your wall or ceiling to an exterior wall or roof, and the duct size and material affect how well the hood performs.
  • Ductwork should slope slightly downward toward the outside to prevent grease and condensation from dripping back into your kitchen.
  • Flexible aluminum duct is easier to install than rigid duct but collects grease faster and can sag if not supported properly.
  • If your hood is recirculating, you cannot convert it to outside venting without installing new ductwork and a damper, which usually requires opening walls or ceilings.

Outside venting: how the duct route works

Outside venting means the hood pulls air through a duct that exits your home through an exterior wall or the roof. The duct carries cooking vapors, grease particles, and moisture directly outside instead of filtering and returning them to your kitchen. This is the most effective way to remove odors permanently.

The duct typically starts at the hood itself, runs horizontally or at a slight downward angle through your wall cavity or above your ceiling, and terminates at an exterior wall or roof vent. The vent opening on the outside has a damper—a flap that opens when the hood runs and closes when it stops, preventing cold air or pests from entering. Most building codes require the duct to slope at least 1/4 inch per foot toward the outside so grease and condensation drain away from the hood rather than back into your kitchen.

The length and path of the duct matter. A long duct run with many bends loses suction power, so the hood has to work harder to pull air through. Most manufacturers recommend keeping the duct run under 30 feet and limiting bends to no more than four 90-degree turns. If your kitchen is far from an exterior wall, you may need a more powerful hood to compensate.

Duct material: rigid versus flexible

Outside venting ducts come in two main materials: rigid metal (usually galvanized steel or aluminum) and flexible aluminum. Each has trade-offs in installation, performance, and maintenance.

Rigid duct is straight sections of metal pipe that connect with fittings and clamps. It resists grease buildup better than flexible duct, stays smooth inside so air flows more easily, and lasts longer. The downside is that rigid duct is harder to install—it requires cutting holes in walls or ceilings, measuring and cutting sections precisely, and securing each section with clamps. If your kitchen layout is complicated or the duct run is long, rigid duct installation often requires opening walls or ceilings, which means hiring a contractor.

Flexible duct is a coiled aluminum tube wrapped in a wire spiral. It is easier to route around obstacles and requires fewer connections, so a homeowner can sometimes install it without opening walls. The problem is that the ridged interior collects grease faster than smooth rigid duct, and the material can sag between supports if not properly braced every 18 inches. Over time, grease buildup in flexible duct reduces airflow and increases fire risk. Flexible duct also creates more noise as air rushes through the ridges.

Many building codes allow flexible duct only for short runs—typically 8 feet or less—and require rigid duct for longer distances. Check your local code before choosing.

Recirculating hoods: when outside venting is not an option

Some range hoods, especially in apartments or kitchens far from an exterior wall, recirculate air instead of venting outside. The hood pulls air through a charcoal filter that traps grease and odors, then returns the filtered air to the kitchen. This avoids the need for ductwork but does not remove moisture or heat from cooking.

Recirculating hoods are less effective at odor removal because the charcoal filter has limits—it works best for light cooking and needs replacement every three to six months depending on use. Heavy cooking or frying overwhelms the filter quickly. Moisture from boiling or steaming stays in your kitchen, which can lead to condensation on windows and walls.

If you want to convert a recirculating hood to outside venting, you need to install ductwork from the hood to an exterior wall or roof, plus a damper on the outside vent. This usually means opening your ceiling or walls to run the duct, which is a significant project. In many apartments, the building structure makes this impossible. Talk to your landlord or a contractor before assuming conversion is feasible.

Installing outside venting: what the process involves

If you are replacing a hood or installing one in a new kitchen, the venting route should be planned before the hood goes in. The duct needs to be in place before you mount the hood to the wall or cabinet.

For a new installation, measure the distance from the hood location to the nearest exterior wall or roof. Determine whether you will use rigid or flexible duct based on the distance, the number of bends needed, and your local building code. Rigid duct is the better choice for runs longer than 8 feet or with multiple bends. Mark the path the duct will take, then cut or drill holes through walls, ceilings, or cabinets as needed. Run the duct along that path, securing it with clamps or straps every 18 inches. Install a damper at the exterior vent opening. Connect the hood to the duct with a transition collar or adapter that matches the hood's outlet size.

If you are replacing an existing hood and the old ductwork is still in place, you can often reuse it if it is in good condition and the new hood's outlet size matches. Inspect the duct for grease buildup, dents, or disconnections. Clean it thoroughly before connecting the new hood. If the old duct is damaged or the outlet sizes do not match, you will need to install new ductwork.

Dampers and exterior vents: preventing backflow

The damper is a one-way flap at the exterior vent opening that lets air out when the hood runs but closes when the hood stops. Without a damper, cold air, rain, or pests can enter your home through the duct when the hood is off.

Most dampers are spring-loaded or gravity-operated and open automatically when air pressure from the hood pushes against them. Check that the damper moves freely and closes completely when the hood is off. If it sticks or does not seal, air leaks around it, wasting energy and allowing odors or pests to enter.

The exterior vent opening itself should have a hood or cap to keep rain out and prevent birds from nesting in the duct. Wall vents typically have a flange that mounts flush to the exterior siding. Roof vents need flashing to seal the hole around the duct and prevent leaks. If the flashing is damaged or missing, water can enter your attic or walls. Inspect the exterior vent twice a year, especially after heavy rain or wind, to make sure it is clear and the flashing is intact.

Maintenance: keeping vents clear and ducts clean

Outside venting requires regular maintenance to work properly. Grease and moisture accumulate in the duct over time, especially in the first few feet after the hood where air is warmest and grease condenses fastest. This buildup reduces airflow and increases fire risk.

Clean the duct at least once a year, more often if you cook frequently or fry regularly. For flexible duct, the easiest approach is to disconnect it from the hood, pull it straight, and wipe the interior with a cloth or brush. For rigid duct, use a duct brush or hire a professional duct cleaning service. Check the exterior vent opening monthly to make sure it is not blocked by leaves, bird nests, or ice. A blocked vent forces the hood to work harder and can cause grease to back up into the kitchen.

Inspect the damper at the exterior vent each season. Make sure it opens when you turn on the hood and closes completely when you turn it off. If it sticks, clean around the hinge or replace it. Check the ductwork for disconnections, dents, or holes. A disconnected duct section sends cooking vapors into your walls instead of outside. Dents and holes reduce airflow and can leak grease.

When to call a professional

You can handle basic maintenance like cleaning the hood filter and wiping the exterior vent. But some venting jobs require a contractor. Call a professional if you need to install new ductwork, especially if it involves opening walls or ceilings, cutting through structural members, or running duct through an attic or crawlspace. A contractor can also assess whether your existing ductwork is adequate for a new hood or whether upgrades are needed.

If your hood is not pulling steam or odor effectively and you have cleaned the filter, the problem is likely a blocked or disconnected duct. A contractor can inspect the entire duct run, locate the blockage, and repair it. If you smell gas or see water dripping from the duct, stop using the hood and call a professional when ready—these are signs of serious problems like a disconnected duct or failed damper.

Frequently Asked Questions

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

No. Venting into the attic sends moisture and grease into a space that is not designed to handle it. This causes mold, rots wood framing, and creates a fire hazard. All range hoods must vent to the outside or recirculate through a filter. Building codes prohibit attic venting.

What size duct do I need for my range hood?

The duct size must match the outlet on your hood. Most residential hoods have 6-inch or 7-inch outlets. Check your hood's manual or the outlet itself to confirm the size. Using a smaller duct reduces airflow; a larger duct wastes energy and may not seal properly.

Why is my range hood making a whistling noise?

Whistling usually means the duct is too small for the hood's airflow, or there is a partial blockage forcing air through a narrow gap. It can also happen if the damper is not opening fully. Check that the duct size matches the hood outlet, inspect the duct for blockages or dents, and make sure the damper moves freely.

Do I need a damper if I vent through the roof?

Yes. A damper prevents cold air, rain, and pests from entering through the roof vent when the hood is off. Roof vents should have a damper built into the vent cap or installed in the duct just inside the roof opening.

How often should I clean my range hood duct?

Clean the duct at least once a year. If you cook frequently, fry often, or use your hood daily, clean it every six months. Signs that cleaning is overdue include reduced airflow, lingering cooking odors, or visible grease around the exterior vent opening.