Microwave Ducts

• A duct that is 140 feet or less moves the microwave exhaust outside of the house quickly and efficiently. However, the configuration of the wall space where the microwave duct will go may determine the need for rectangular-to-round transition adaptors, elbows and wall caps. These parts will add extra length to the ductwork. A typical transition adaptor may run 5 feet. A 90-degree elbow joint may be 10 feet. While a wall cap will add about 40 feet of duct, a roof cap may add about 24 feet.
  
  

Outside Top Exhaust Mount

• A microwave can be exhausted through the roof of a house via an outside top exhaust mount. The ductwork should be mounted between two wall studs, threaded through the wall up to the vent under the roof cap. The microwave mounting plate is installed with toggle bolts on the wall so that the microwave exhaust damper lines up with the duct. The damper should be adjusted to open and close freely to push exhaust from the microwave into the duct. The duct is lowered to meet the exhaust adaptor. It's sealed into place with duct tape.
  
  

Outside Back Exhaust

• A microwave oven can also be mounted to the exhaust directly through the wall, which is called the outside back exhaust. A horizontal vent is cut into the wall through which the duct will run. The duct extends through the outside wall where it will be sealed to a wall cap. The exhaust adaptor is moved to the back of the microwave to face the wall vent. The blower motor is adjusted so that its fan blows the exhaust out through the exhaust adaptor at the rear of the microwave. The duct is pulled through the wall to meet the exhaust adaptor and is sealed into place with duct tape.
  
  

Considerations

• A shorter run of duct will minimize dangerous levels of grease and debris in the ductwork. However, you may need to use elbow-duct pieces to get around corners, plumbing, wiring or structural anomalies to reach the duct's outdoor destination. Some microwave ovens have blower motors, so they exhaust out the fronts of the ovens. The blower motor must be moved and adjusted, so it exhausts out through the wall duct. Other microwave ovens provide recirculation exhaust systems, which means that they do not need exhaust ducts.