How to Clean the Ductwork Inside Your Range Hood

Grease accumulation inside your range hood ductwork is invisible until it becomes a problem—either a fire hazard or a exhaust that barely pulls smoke anymore. The ductwork is the forgotten part of the hood system: you clean the filter regularly, maybe wipe the exterior, but the inside of the duct itself collects a thick, sticky layer of cooking vapors that harden over time. This buildup reduces airflow, makes your hood work harder, and creates genuine fire risk. Cleaning it is straightforward, takes an afternoon, and keeps your kitchen exhaust system working like it should. The key is accessing the duct safely, breaking up the grease deposit, and pulling it out—not pushing it deeper into the system.

1. Kill Power First. Switch off the range hood using the wall switch, then flip the breaker for the unit if it's hardwired. Wait 5 minutes for any residual moisture and grease vapor to settle. This matters for safety and to avoid electrical shock. If your hood is plugged in, unplug it from the outlet.
2. Disconnect Hood End. Locate where the hood connects to the duct—usually a 6-inch or 8-inch diameter aluminum or flexible duct. Loosen the clamp that holds it in place using a screwdriver or adjustable wrench. Slide the duct off the hood connection. Have a bucket or towel ready underneath, as loosening the connection will release trapped grease and dust.
3. Free Exterior Access. If you can reach your duct where it exits the home—usually through a wall or roof—disconnect it there as well. Loosen the clamp at the exit point and remove the exterior duct collar or cap. This gives you clear access to both ends of the interior ductwork. If you cannot safely access the exterior, you can work from the hood end alone; it will take longer but is still effective.
4. Scrub Grease Loose. Insert a dryer vent brush or flexible ductwork brush into the duct from the hood end. Push it through the length of the duct in short, forceful strokes. Twist as you go. The goal is to loosen the hard, caked grease layer so it falls into the duct rather than staying stuck to the walls. This takes 10 to 15 minutes for a typical 6-inch duct run of 8 to 10 feet. You'll feel resistance as the brush hits heavy deposits; lean into it.
5. Vacuum Out Debris. Once you've loosened the deposits with the brush, use a shop vacuum with a hose to pull out the loosened grease, dust, and debris. Insert the hose into the duct from the hood end and work it along the interior length. You'll hear and feel the suction pulling material out. Make multiple passes. This step is messy and produces dark, sticky runoff in the vacuum—that's normal. Empty the vacuum canister into a trash bag when finished.
6. Blast With Air. Using a can of compressed air or an air compressor set to 40–60 psi, blow air through the duct from the exit end toward the hood end. This dislodges any remaining grease particles clinging to the interior walls and pushes them toward the hood. Work in 2-foot sections, moving the nozzle back and forth. The grease and dust will blow out the hood end into a bucket or onto a catch cloth.
7. Degrease Hood Opening. With the duct removed, the hood intake opening is exposed. Use a cloth and degreaser to wipe down the interior walls and the back of the hood opening. Use your brush or a small bottle brush to scrub the opening where the duct connects. This prevents cleaned ductwork from immediately re-fouling from a grimy hood chamber. Degreaser and hot water work best; let it soak for a minute before scrubbing.
8. Check For Damage. While the duct is off and accessible, look for cracks, dents, or loose seams in the ductwork itself. Small dents don't matter. Cracks or separated seams are a problem—they allow air to escape and defeat the hood's ability to pull smoke. If you find damage, mark the location and plan to replace that section. Use a flashlight to look inside the duct as well; if you see rust, moisture, or mold, those sections may also need replacement.
9. Reconnect Hood End. Slide the indoor end of the ductwork back onto the hood's connection point. Tighten the clamp securely with a screwdriver or wrench until it's snug but not so tight that you strip the threads. The connection should be airtight; if air leaks around the seam, your hood won't pull properly. Give the connection a gentle tug to confirm it's seated.
10. Seal Exterior End. If you disconnected the duct at the exterior exit, slide it back into the exit collar and tighten the clamp. Make sure the exterior duct cap is seated and sealed. If your hood vents through the roof, ensure the flashing is intact and the cap points downward so rain drains away. Test that the duct feels secure by gently pulling and twisting.
11. Verify Airflow Returns. Flip the breaker back on or plug the hood back in. Turn the hood on at the lowest fan speed and listen for any strange noises or rattling from the ductwork. Airflow should feel noticeably stronger than it did before—hold your hand near the cooktop to feel the suction. The hood should pull smoke or steam away from the cooking surface without hesitation. Run it for 5 minutes to confirm stable operation.
12. Schedule Next Cleaning. Make a calendar note to repeat this cleaning process every 6 to 12 months, depending on how often you cook and what you cook. High-heat cooking, frying, and grilling create more vapor buildup than steaming or baking. If you cook multiple meals a day or use your wok frequently, clean every 6 months. If you cook occasionally, annually is fine. Regular cleaning is far easier than waiting until the hood barely pulls at all.