Range hoods require the installation of 7-inch round or 3 1/2-inch by 10-inch rectangular ducts to the outside unless the installer chooses to use them as recirculating vents. Recirculating vents filter the smoke and grease from the air before releasing it back into the room.
When installing range hood vents, it is essential that the ducts lead outside the home. Ducting the vent to an attic or other space in the home is dangerous. The grease buildup from improperly vented hoods can cause a fire hazard, while the moisture from cooking can encourage the growth of mold.
Many of the range hoods currently installed as recirculating devices are convertible to outdoor vents with the installation of the correct type of duct. When the range sits beside an outside wall, ducting through the wall is often the easiest option. When the range is not placed against the outside of the home, a roof vent is sometimes necessary. Outside the home, the installation of a vent cap prevents animals and cold air from entering the home.
When considering venting the range hood, homeowners may also want to think about installing a newer hood. Many of the contractor-installed hoods in new construction have loud fans and relatively low air volume movement. Upgraded vents help to reduce the noise of operation while removing more moisture, grease and cooking odors.