Replace a Recirculating Range Hood With a Ducted One
A recirculating hood filters grease and blows the steam, smoke, and smell right back at you. Venting outside is the single biggest air-quality upgrade in a kitchen, and the hood is the easy part.
A ductless hood is a fan with a charcoal filter. It catches some grease and does nothing about moisture, carbon monoxide from a gas range, or the smell of last night’s fish. A ducted hood pushes all of it outdoors, and the difference on a humid August night with three burners going is dramatic. The replacement itself is a two-hour job; the real project is the duct run between the hood and the outside world, and that is what you plan first.
Size the fan and find the path
For a standard 30-inch range, 300 to 400 CFM is plenty; a pro-style gas range wants closer to 600. Anything over 400 CFM requires makeup air under most codes, one more reason not to oversize. Then trace the route: up through the cabinet and straight out the wall behind it, or up through the cabinet and roof. Every 90-degree elbow costs about 15 feet of equivalent duct, so a 400 CFM hood through 25 feet with two elbows is really moving perhaps 250. Keep it short, keep it rigid, and never use flexible plastic or foil duct for a kitchen hood.
Remove the old hood
Kill the breaker and test the circuit dead at the hood. Pull the filters, open the wiring cover, and disconnect the cable. Support the hood while backing out the mounting screws. Most hoods offer both a top and a rear exhaust knockout; you will open the one that matches your duct route.
Cut the cabinet and the wall
Use the hood’s template to mark the duct opening on the cabinet bottom and jigsaw it out, then cut the cabinet back or top to continue the run. Before any exterior cut, drill a locator hole from inside and check outside for siding seams, electrical service, and gas meters. Cut the exterior hole a half inch larger than the duct.
Run rigid duct and cap it
Assemble the duct with crimped ends pointing in the direction of airflow, seal every joint with foil tape, and support horizontal runs every 4 feet. Bed the wall cap in exterior caulk with its damper swinging freely and screw it to the sheathing. For a roof cap, slide the flange under the shingles above, lap it over the shingles below, and seal the nail heads. A second damper at the hood end stops the winter backdraft that frosts hoods.
Mount and wire the hood
Tape the duct transition to the hood’s knockout, lift the hood into place, and screw it to the cabinet bottom, keeping the bottom edge 24 to 30 inches above the cooktop. Feed the house cable through the clamp, connect black to black, white to white, ground to the green screw, and close the cover. Restore power and test fan and light.
Test for leaks
Run the fan on high and hold a tissue at every duct joint you can reach. Any flutter means grease will collect there, so tape it again. Confirm the exterior damper opens fully.
Never vent a range hood into an attic, soffit, or crawl space, and never share its duct with a dryer or bath fan. If the hood circuit is a cord-and-plug and you are converting to hardwired, or if you need a new circuit for a bigger fan, that is permit work. Gas ranges plus a big hood may need a makeup-air damper; ask the inspector.
The hood is a fan. The duct is the appliance.
Keep it moving
Wash the filters monthly in the dishwasher, and once a year vacuum the duct entry and check the exterior damper for grease or bird nests. A properly ducted hood with a short, sealed run will move rated air for decades, and you will notice its absence the first time you cook at a friend’s house with a recirculating one.
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