How to Measure for Duct Opening Size for Small Over the Range Microwave

Over the range microwaves with exhaust fans are great for getting rid of smoke and odors from food cooking on the stove beneath them. To hook up these exhaust fans properly, it is crucial to measure the ducting correctly.

Step 1 - Measure the Exhaust Opening on the Appliance

Before installing the microwave range hood, look at the back and top portions of the appliance to determine where the air from the fan will be vented out of. Using a tape measure, find the distance across the widest part of the circle; in other words, find the diameter of the exhaust port. Round the measurement to the nearest whole number. For example, if the vent diameter measures 7 3/4 inches, the diameter should be rounded to 8-inches

Step 2 - Measure the Ducting Coming from the Wall

Once you've found the size of the opening on the appliance itself, measure the exhaust duct that runs through the walls of the house and vents to the outside. The reason the diameter of the exhaust duct must be found is to ensure it will fit with the opening on the appliance itself. Once again round to the nearest whole number if necessary.

Step 3 - Link the Ductwork

Using the two measurements, simply link the two pieces of ducting with a coupler if they are the same diameter or with the proper size reducer if they are different. If the ducting measures 10-inches and the exhaust port on the microwave range hood is only 8-inches, a 10-inch to 8-inch reducer will be needed.