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Over-the-range microwaves typically include a ventilation system that serves as a vent hood for the range's cooktop. Like any ventilation equipment, the microwave fan should be vented to the outdoors to be effective. This requires a duct running through an exterior wall or through the roof. The alternative to a ducted fan is a recirculating fan, which simply blows the air and cooking vapors through a filter and back into the kitchen; there is no real ventilation. The following is an overview of the basic steps for installing an over-the-range microwave with a vent fan ducted to the outdoors.Continue to 2 of 10 below.
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Cut Holes for the Vent Duct
Microwaves can be vented through the back of the unit, with the duct running straight back and through the wall behind the unit, or they can be vented through the top of the unit, with the duct running up to the roof or a higher point on the wall. Use the template provided with the microwave to mark the hole for the vent duct on the wall or the bottom of the cabinet.
To run the duct through a wall: Mark the wall, then cut out the drywall using a drywall saw. If you run into a stud behind the drywall, you'll have to move the vent to avoid it, or plan to add a little jog in the duct run. This is a load-bearing wall, and you can't cut out a stud unless you build a structural header over the opening (similar to a window frame). It's much easier to move the vent. Use a small drill bit to drill through the outside wall to mark the center of the hole before going outside to mark and cut the hole in the exterior side of the wall.
To run the duct up through a cabinet: To vent up through the cabinet and soffit, into the attic, and through the roof, use the template to mark the underside of the cabinet, then cut the hole. Cut additional holes as needed to complete the duct route to the attic and through the roof.Continue to 3 of 10 below.
03 of 10
Install the Duct
Install the ductwork and outdoor vent cap, as applicable. The duct should be rigid metal rectangular or round duct. Microwave vent openings often are rectangular, and you can transition to a round duct with an adapter fitting. You will connect the interior end of the duct to the microwave after installing the microwave unit.Continue to 4 of 10 below.
04 of 10
Install an Outlet in the Cabinet
An over-the-range microwave oven usually plugs into an electrical outlet installed inside the upper cabinet above the microwave. Microwaves typically are rated for 15 amps, but they should be fed by a dedicated 120-volt, 20-amp circuit. This is because the high wattage of a full-size microwave plus a vent fan can exceed the safe capacity of a 15-amp circuit. Install the circuit cabling, electrical box, and 20-amp electrical outlet, making sure the outlet is within reach of the microwave plug. Follow all local building code requirements for the circuit installation.Continue to 5 of 10 below.
05 of 10
Mount the Wall Bracket
Draw a vertical line at the center of the cabinet space, using a level. Position the wall-mount bracket so it is aligned with the centerline. Adjust the height based on the cabinet and microwave configuration, following the manufacturer's instructions. Mark the mounting holes, then remove the bracket. Drill pilot holes for the mounting screws or anchors. If a mounting hole does not line up with a wall stud, drill a larger hole for a heavy-duty hollow-wall anchor (such as a toggle bolt). Mount the wall bracket with screws and anchors, as appropriate.Continue to 6 of 10 below.
06 of 10
Drill Mounting Holes in the Cabinet
Use the template that comes with the microwave to mark the mounting holes on the bottom of the cabinet. Drill the holes through the bottom panel of the cabinet, as directed by the manufacturer. Microwaves usually mount to the cabinet with bolts, so the mounting holes go all the way through the cabinet panel. Drill a larger hole for the microwave's power cord.Continue to 7 of 10 below.
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Configure the Vent
Make all necessary adjustments to the microwave vent to prepare for the installation. For example, if the unit is set for back-venting at the factory, you may need to reconfigure the vent system for top-venting. Follow the manufacturer's instructions for all adjustments.Continue to 8 of 10 below.
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Install the Microwave
Find a helper or two for mounting the microwave to the wall bracket and cabinet. Lift the unit into position, and feed the power cord through the hole in the cabinet. Hook the lower edge of the unit onto the wall bracket, then tilt the unit so its back is flush against the wall. Insert the mounting bolts through the bottom of the cabinet and into the threaded holes in the top of the unit, then tighten the bolts.Continue to 9 of 10 below.
09 of 10
Connect the Duct
Connect the duct to the vent opening of the microwave, using an adapter fitting, if necessary. Seal the connection with metal duct tape approved for high-heat ductwork. Do not use standard plastic duct tape.Continue to 10 of 10 below.
10 of 10
Plug in the Microwave
Install the grease filter on the microwave, as applicable. Plug in microwave to the electrical outlet. Test the microwave for proper operation by heating up a glass of water. Do not run the microwave empty.