A microwave oven designed to be mounted over a cooking range typically has a built-in vent fan and light fixture designed to illuminate the stovetop. These microwaves usually fit between adjoining wall cabinets and below a specialty upper cabinet that hides the vent connections and electrical outlet. When added to an existing kitchen, this type of microwave replaces the existing range hood and vent fan.
While some over-the-range microwaves use simple recirculating fans that do little more than filter cooking vapors and return the air into the room, the better types have external vents that exhaust to the outdoors via ductwork that runs through the roof or an exterior wall.
Every microwave oven will have specific instructions for installation, but all follow a similar process:
- Installing an electrical outlet (and new circuit, as needed)
- Cutting holes for the duct and vent cap
- Installing the duct and vent cap
- Mounting the wall bracket
- Drilling holes in the cabinet
- Preparing the microwave vent
- Mounting the microwave
- Connecting the ductwork
- Finishing the project
Installing an over-the-range microwave oven requires basic carpentry skills and extensive experience working with electrical circuits. A dedicated breaker must be installed (ideally by a licensed electrician), and you must ensure the ductwork is water-tight when vented through the roof. If you are not confident in your ability to accomplish these steps or do not have advanced experience working with circuits, hire a handyperson, carpenter, or electrician for some or all of this work.
Equipment / Tools
- Tape measure
- Drill with bits
- Drywall saw
- Reciprocating saw or jigsaw
- Metal shears (if needed)
- Caulk gun
- Stud finder
- Spade bit or hole saw
- Over-the-range microwave oven
- Metal duct sections
- Transition fitting for microwave vent (if needed)
- Vent cap (for roof or side wall)
- Sheet metal screws
- Exterior caulk or roofing cement
- 20-amp circuit breaker 20-amp receptacle, wall box, and 12-gauge NM cable
- Electrical box
- 20-amp receptacle
- 12-gauge NM cable
- Wood screws
- Metal duct tape
Install an Electrical Outlet
Building codes require that a microwave oven have a dedicated 20-amp circuit that serves no other outlets of appliances. This likely means that you'll need to add a new electrical circuit and outlet within reach of the oven's power cord. Most microwaves are configured so the power cord extends up through the floor of the upper cabinet above the microwave, so the best place for this wall outlet is inside the upper cabinet.
Note: 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.
This is a complicated job that requires you to run a new electrical cable through walls to the main circuit breaker panel, to install and connect an electrical outlet, and to finalize the circuit hookup at the circuit breaker panel. Unless you are experienced and very confident in your skills, this kind of electrical work is best left to a professional electrician.
Cut Holes for the Ductwork and Vent Cover
As you begin the installation, you'll need to determine whether to vent your microwave through the back of the unit, with the ductwork running straight back and through the exterior wall, or through the top of the unit, with the ductwork running up through the cabinet and ceiling to the roof. This is sometimes a matter of simple convenience and accessibility.
Either method will work, but your vent fan will work most efficiently with a short, straight run of ductwork. Usually, this means that exterior wall installation of the vent is the easiest option, but where it is impossible to do this, or where you don't want to mar the exterior siding with a vent cap, you can run ductwork up through to the roof, attaching it with roof vent cap fitted into the shingles.
Use the template provided with the microwave to mark the hole for the vent duct on the wall or the bottom of the upper cabinet.
To run the ductwork through the wall:
Tape the provided paper template onto the interior wall. Mark the location of the vent opening on the wall. Cut out the opening in the drywall with a drywall saw or jigsaw. Mark an outline for the vent cap opening on the exterior wall sheathing, and drill locator holes through the sheathing and siding to the outdoors.
From the outside, mark an outline of the vent cap on the siding, using the locator holes for reference. Cut out the exterior siding and sheathing, using a reciprocating saw or jigsaw. This can be a relatively easy job if you have standard lap siding, but brick or stucco exteriors may require considerable work and additional tools.
To run the ductwork through the roof:
Tape the paper template to the bottom of the upper cabinet. Outline the location of the vent opening on the bottom of the upper cabinet. Drill holes at the corners of the outline, then cut out the vent opening, using a jigsaw or reciprocating saw.
Mark and cut out additional openings on the top of the upper cabinet, the ceiling, and the attic floor, where the ductwork will run. From inside the attic, outline the shape of the roof cap collar on the roof sheathing. Drill pilot holes then cut a hole in your roof for the vent roof cap.
Install the Duct and Vent Cap
All duct should be rigid metal and can be either rectangular or round in shape. You may need a transition fitting to make the connection between the vent cap collar and the first duct section.
From the exterior or roof, insert the collar of the vent cap into the hole you have cut into the siding or roof. Secure the vent cap in place following manufacturer's instructions. This will usually mean applying silicone caulk or roofing cement, then securing the flanges on the vent cap with nails or screws. Roof caps are usually self-flashing, with metal flanges that slide underneath overhanging shingles and are secured with roofing nails. Caulk beneath the flashing with roofing cement to prevent leaking. Wall vent caps should be sealed in place with silicone caulk.
Once the cap is installed, secure the first section of duct to the inner collar on the vent cap, using sheet metal screws. Seal the joint with metal duct tape (not plastic tape). Continue extending the duct with additional sections, securing each joint with sheet metal screws and metal duct tape. Cut the last section of duct to fit, using metal shears, so it is flush with the wall surface (for back-venting) or the top of the upper cabinet (for top-venting).
Flexible plastic or corrugated aluminum duct, although easy to install, is not recommended, and it may be prohibited by the local building code. These ducts can collect grease on their inside surfaces, creating a potential fire hazard.
Mount the Wall Bracket
This step may require some carpentry skills. Different brands of microwaves differ somewhat in how they are hung from the wall, but most use a bracket that is installed on the wall behind the unit. The oven hangs on the bracket and is secured near the front with bolts driven down through the top cabinet and into the case of the oven.
If you are lucky enough to have a wall stud positioned at the exact center of the bracket, you can drive the center mounting screw for the bracket directly into this stud. If not, most installation pros suggest removing a section of drywall and installing a strip of plywood across the wall where the oven bracket will be attached. The plywood strip is anchored to wall studs and provides secure backing for attaching the mounting bracket.
The microwave oven should come with paper templates that assist you in attaching the wall bracket, drilling the bottom of the upper cabinet, and attaching the mounting bolts for the oven.
Start by drawing a vertical line at the center of the cabinet space, using a level. If your oven comes with a paper template, tape this to the wall as a guide. Use a studfinder to locate the wall studs. If one of the wall studs aligns with the centerline, you can continue to the next step. If not, you will first need to remove drywall, then cut and install a plywood backer strip across the wall at the level where the bracket will be installed. Anchor this backer strip securely to wall studs.
Position the wall-mount bracket on the wall so it is aligned with the centerline. Adjust the height of the bracket based on the cabinet and microwave configuration, following the manufacturer's instructions. Make sure the bracket is level. Mark hole locations for the mounting screws. Remove the bracket, then drill pilot holes at the marked locations.
Position the bracket on the wall, make sure it is level, and anchor it with wood screws driven through the bracket and into the pilot holes or wall studs.
Drill Holes in the Cabinet
Holes in the bottom of the upper cabinet are needed for the microwave's power cord and unit mounting bolts.
To make the holes, tape the paper template provided with the microwave to the bottom of the upper cabinet. Mark the location for both the mounting holes that will secure the microwave oven and a larger hole for the power cord. Drill holes for the mounting bolts using an appropriately sized twist bit. Drill the power cord hole with a spade bit or hole saw.
Prepare the Microwave Vent
Make any necessary adjustments to the microwave's vent fitting. 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 alterations.
The exhaust openings for most microwaves are rectangular in shape, and if you are using round ductwork, you may need to use a transition collar to convert the round shape of the ductwork to a rectangular shape that can be connected to the microwave.
Mount the Microwave
Microwave ovens are heavy, and this step calls for a helper or two as you lift the oven into position and secure it.
Lift the microwave up into position, and feed the power cord up through the hole in the cabinet. Hook the lower edge of the microwave onto the wall bracket, then tilt the unit so its back is flush against the wall.
While a helper holds the microwave in position, insert the mounting bolts down through the bottom of the cabinet and into the threaded holes in the top of the unit. Tighten the bolts securely.
Connect the Ductwork
Connect the metal ductwork to the vent opening on the microwave.
For back venting:
If the duct installation has been correct, the microwave's vent fitting should slide smoothly into the collar of the exterior vent cap. But often minor adjustments are needed to make the connection between microwave vent and the duct.
For top venting:
You will need to cut and fit the final section of duct to run from the duct entering the top of the upper cabinet and the microwave's vent fitting at the bottom of the upper cabinet. This is normally a simple short length of rigid metal duct.
Once the connection is complete, seal any joints that are accessible, using metal duct tape.
Finish the Project
Your microwave oven installation is nearly complete. Finish the job by installing the grease filter on the microwave, as applicable. Plug the microwave oven into the electrical outlet, and turn on the circuit breaker. Test the microwave for proper operation by heating up a glass of water. Do not run the microwave empty.