How to Cut a Metal Vent for a Microwave

Mount the microwave to the wall so that you can perform an accurate measurement for the vent length.

Place a tape measure at the top of the microwave where you see the rectangular vent opening and measure all the way to the location on the exterior wall hole. If your vent requires turns, measure each section separately and add them together.

Subtract 3 1/4 inches from the measurement to allow for the vent extension piece and the round transition piece, which connect the pipe to the actual microwave. This final measurement is the total length for the vent.

Lay the metal duct on a table or on the floor. Measure the proper distance from one end and mark the location with a pencil. Rotate the vent in a circle until the pencil line extends all the way around it.

Locate a pair of heavy work gloves and put them on -- metal duct edges are sharp. Cut upward through the end of the duct -- perpendicular to the duct's edge -- using a pair of tin snips, which operate just like scissors. Continue cutting until you reach the pencil line.

Turn the snips sideways until they are in line with the pencil mark. Proceed to cut all the way around the pencil line until you reach the starting point.

Discard the excess portion of the metal duct, and install the remaining section in the wall opening per the microwave manufacturer’s instructions.