The Options for Venting an Over-the-Range Microwave

Built-In Venting

• Over-the-range microwaves do double duty as an appliance as well as a venting system. With their built-in exhaust system, it's usually not necessary to have a separate duct system or exhaust fan. The microwave vents the smoke and steam from the range it's placed over to the outdoors through a duct or recirculates it inside the home.

Inside Venting

• The inside venting system is usually installed and ready for operation on most over-the-range microwaves. No other venting is necessary. While it is still considered a ventilation system, it does not vent the smoke and air but instead recirculates the air with a fan. Most recirculating microwave systems have a charcoal filter installed on the microwave to trap odors.

Outside Venting

• Ductwork is connected to the microwave when venting it to the outside. The ductwork may run from the top -- vertical duct -- or back -- horizontal duct --of the microwave. The duct piece configuration varies widely based on the where the ductwork originates from the microwave and how it's positioned within the wall. Most configurations require several pieces of straight duct pieces, elbows and a roof cap. Outdoor venting should allow for a direct route as much as possible, with the use of as few elbow pieces as possible. This facilitates clear venting and prevents blockages.

Warnings and Tips

• Over-the-range microwaves do not have as powerful a venting system as separate hoods, fans and other ventilation systems. While they are usually sufficient to control air flow, some ranges -- particularly those larger than 36 inches wide -- may require a separate venting system. Always refer to the range owner's manual or contact the manufacturer to verify venting requirements.