Never vent a range hood into the attic; it is illegal and unsafe.
- Attic venting causes moisture, mold, and grease fire hazards.
- Always vent to the outdoors through the roof or wall with rigid metal duct.
- Ductless hoods are a compromise but do not remove moisture.
Why attic venting is a bad idea
Venting a range hood into the attic pushes moist, greasy air into an enclosed space. That air carries water vapor from cooking, which condenses on cold surfaces. Over time, this leads to mold growth and wood rot in roof rafters and insulation. Grease also coats attic surfaces, increasing fire risk. Most local building codes explicitly forbid this practice. Even if your attic has vents, they are not designed to handle the volume of air from a range hood.
What the building codes say
The International Residential Code (IRC) requires range hoods to vent to the outdoors. Section M1503.1 states that exhaust ducts must terminate outside the building. Attic spaces are not considered outdoors. Local amendments often repeat this rule. Inspectors will flag attic venting during a home sale or renovation. Failing to comply can result in fines or required rework.
The moisture and mold problem
Cooking produces steam, especially when boiling pasta or simmering soups. A range hood captures that steam and sends it through ductwork. If the duct ends in the attic, the moisture has nowhere to go. In winter, warm humid air hits cold roof sheathing and condenses. This creates ideal conditions for mold and mildew. Over time, insulation loses its R-value when wet. Wood rot can weaken structural members.
Fire and grease hazards
Grease particles travel with the air from your cooktop. They accumulate inside ductwork and on attic surfaces. Grease is highly flammable, especially when combined with heat from recessed lights or wiring. A small spark could ignite accumulated grease. This is a serious fire hazard that insurance may not cover if code violations are found.
Proper venting options
The correct way is to run ductwork to the outside. You can vent through the roof using a roof cap, or through an exterior wall with a wall cap. Use smooth metal duct, not flexible foil, to reduce grease buildup. Ensure the duct is as short and straight as possible. If you cannot vent outside, consider a ductless range hood with charcoal filters, but know it recirculates air and does not remove moisture.