How to Clean Kitchen Exhaust Ductwork

Kitchen exhaust ductwork collects grease the way gutters collect leaves, except what collects in your ducts is a genuine fire hazard. Every time you cook, oils vaporize and travel up through the hood into the ductwork, where they condense and build up layer by layer. Within a year or two, that buildup restricts airflow so badly your hood barely whispers, and the accumulated grease becomes combustible. The difference between a functioning exhaust system and a fire waiting to happen is usually just a Saturday afternoon and some elbow grease. When your hood sounds strained or the kitchen fills with smoke even with it running, the ductwork needs cleaning. This job is straightforward—disconnect the ductwork at access points, scrub it thoroughly with degreaser, and reassemble. No special skills required, just persistence and the willingness to get dirty.

1. Kill the Power First. Switch off the exhaust hood and flip the breaker that controls it. If it's hardwired, locate the breaker in your electrical panel. If it's plugged in, unplug it. Wait a full minute before touching anything—the motor may still be spinning. This prevents accidental startup while you're working inside or near moving parts.
2. Clear the Hood Opening. Open the hood and slide out any mesh or baffle filters. If your hood has a removable grease trap or drip pan, pull that out as well. These parts are usually held by friction or a simple latch. Set them aside—you'll clean them separately. This gives you clear access to the hood's interior and the first section of ductwork.
3. Disconnect at the Hood. Follow the ductwork from the hood to where it exits the cabinet or wall. Most ductwork is connected with a single screw collar or band clamp at the hood outlet. Loosen the screw or clamp with a screwdriver or wrench and slide the duct away from the hood. If the duct is sealed with tape or caulk, carefully cut or peel it away. Mark the ducting with tape so you know which way is up and which direction it came from.
4. Pull from the Outside Out. Go outside to where the ductwork exits the building. You'll see a vent cap or damper assembly. If it's attached with screws or rivets, unscrew or drill out the rivets to separate the duct from the exterior hood. If it's caulked shut, cut the caulk with a utility knife. Carefully pull or slide the ductwork out from the wall or roof. This is often the dirtiest and stickiest part of the job.
5. Organize Your Workspace. Lay out the disconnected ductwork on a flat surface—a driveway or tarp works well. Gather a stiff bottle brush or plumbing snake brush, degreasing spray (commercial kitchen degreaser or TSP), old rags or paper towels, and a five-gallon bucket of warm water. If the buildup is very thick or you're dealing with rigid ductwork, a length of PVC pipe or wooden dowel can help you push the brush through. Have a scraper or putty knife nearby for stubborn sections.
6. Soak and Soften. Stand the ductwork on end (or lay it at a slight angle so liquid doesn't pour out the other end) and spray the interior generously with degreaser. Work section by section if it's a long run. Let the degreaser sit for 10 to 15 minutes so it can break down the grease. This waiting period does half the work for you—don't skip it. You should see the grease begin to soften and run.
7. Scrub Every Section. Insert a stiff brush into the ductwork and scrub vigorously in all directions, twisting and pushing to dislodge the grease. Work your way through the entire length of the duct, moving the brush back and forth and rotating it to catch all angles. The loosened grease will come off in clumps. For long straight sections, push the brush through from one end to the other, then pull it back, repeating several times. As grease dislodges, it will fall out or accumulate at the low end.
8. Rinse Until Water Runs Clear. Once you've scrubbed all sections, spray or pour warm water through the ductwork to rinse out loosened grease and degreaser residue. Tilt the ductwork so water runs toward the low end and drains out. You may need to spray again and let it drain. Repeat until the water runs clear and you see no more grease or foam. This is critical—any remaining degreaser will interfere with sealing later.
9. Don't Forget the Filters. Spray the mesh filters and grease trap with degreaser and scrub them with an old brush or cloth. Let them soak in a bucket of warm water mixed with degreaser for 15 minutes if they're very dirty, then scrub again. Rinse thoroughly with clean water and let them dry. These accumulate a lot of the heavier grease and are easier to clean when separated from the main ductwork.
10. Check for Hidden Damage. While the ductwork is disconnected, examine it for dents, tears, or corrosion. Look especially at seams and joints. Minor dents don't matter, but holes or separated seams will need repair tape or replacement sections. If you spot damage, plan to address it before reinstalling. Clean ductwork that leaks air into walls or crawlspaces defeats the purpose.
11. Seal at the Hood. Carefully slide the ductwork back onto the hood outlet, aligning it properly. Tighten the collar clamp or screw firmly but don't overtighten—metal can crimp. Seal the joint with aluminum foil tape or HVAC mastic compound, wrapping around the seam completely. Do not use regular duct tape—it fails under heat. Reinstall the filters and grease trap in their original orientation.
12. Seal the Exterior. Carefully push the ductwork back through the wall or roof opening until the exterior hood or damper aligns with the opening. Screw or rivet it back in place. Apply a bead of paintable silicone caulk around the perimeter where the ductwork meets the wall or roof to seal out weather and pests. Smooth the caulk with a wet finger. Allow it to cure per the product instructions before using the hood.
13. Verify Strong Airflow. Restore power to the hood by flipping the breaker back on. Turn on the hood and listen—it should sound noticeably quieter and more efficient than before. Hold a piece of paper or thin cloth near the hood opening; the pull should be strong and consistent. If airflow seems weak or the hood is still loud, you may have missed a section of buildup or the ductwork may need a second pass. Check the exterior to confirm air is being expelled, not just circulating inside the duct.