What is the best roof vent for a range hood?
Short answer. The best roof vent for a range hood is a metal roof cap sized to the hood's duct, often 6 to 10 inches, with a backdraft damper and no fine screen that can clog with grease. The duct itself must be smooth, airtight metal that runs straight outdoors, never into the attic, soffit or ridge vent.
What a good range hood cap has
- Full size collar: matched to the hood's outlet. Necking an 8 inch hood down to 6 inches at the cap chokes airflow and makes the fan loud.
- Metal body: galvanized steel or aluminum, which tolerates heat and grease.
- Backdraft damper: to stop outside air and pests when the hood is off.
- A bird guard, not insect screen: fine screens trap grease and clog.
- A tall or angled hood: so rain does not fall straight into the duct.
Code points worth knowing
- The residential code requires kitchen exhaust ducts with smooth inner walls, airtight construction and a backdraft damper, made of metal and independent of other exhaust systems.
- Exhaust may not end in the attic, a soffit, a ridge vent or a crawl space.
- Hoods that can exhaust more than 400 cubic feet per minute need makeup air, so high powered hoods affect more than the roof.
Roof or wall?
On an island or a range far from an exterior wall, a roof cap is often the shortest path. On an exterior wall, a wall cap avoids a roof penetration. Either way, a short, straight run with few elbows works best.
Upkeep
Grease builds up in the cap and can stain the shingles below it. Check the cap once a year for buildup and a damper that sticks. If shingles around the cap are stained or soft, have the flashing checked. See roof flashing explained and common roof leak causes.