How to Choose and Install an Over-the-Range Vented Microwave

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A vented over-the-range microwave is a good solution for many kitchens. A standard countertop microwave oven takes up a large footprint, and in small kitchens with limited counter space, this can be a big inconvenience. An excellent space-saving alternative is a vented over-the-range microwave (OTR) oven, which combines the functions of a microwave, vent hood exhaust fan and task light. If you choose a microwave oven with convection heating, which can brown foods by circulating hot air, the appliance can become an important workhorse in your kitchen.

As Consumer Reports observes, an over-the-range microwave oven also offers the advantage of letting you match the microwave with the rest of your kitchen appliances. When paired with appliances from the same manufacturer and topped by an upper cabinet that matches the style of the rest of your kitchen, the microwave will blend in quite seamlessly.

How an Over-the-Range Microwave Works

A vented over-the-range microwave oven can be mounted in several ways, but most typically, it is positioned above the cooking surface of a range or cooktop and beneath a short upper wall cabinet that conceals the connections for the ductwork that vents the appliance to the outdoors. This appliance combines a standard microwave or convection/microwave oven in a cabinet that also incorporates an exhaust fan with charcoal filters as well as a downward-directed task light to illuminate the cooking surface.

On vented microwaves, the duct outlet can be adjusted in one of three ways: directed upward if you plan to direct-vent the appliance up through the roof; backward if you plan to direct-vent out through the kitchen wall behind the cabinet; or closed off entirely if you plan to configure the appliance so it is self-venting.

Self-venting, in which kitchen air is merely recirculated and cleaned by a charcoal filter, is not a recommended configuration since it does nothing to actually expel fumes to the outdoors. Self-venting should never be used for appliances that burn natural gas or liquid propane, which produces carbon monoxide and moisture that need to be exhausted from the kitchen.

Choosing a Vented Microwave Oven

As with countertop microwaves, you have many options when choosing a vented over-the-range microwave oven.

  • Standard microwave vs. convection: Standard microwaves are familiar to almost everyone, but you might want to consider a combination convection microwave if you do a lot of cooking. Convection microwaves are somewhat larger in size and have the ability to brown foods by circulating superheated air through the oven. You can even roast meats in these units, which makes them very useful for preparing large meals.

  • Capacity: Over-the-range microwaves are typically slightly smaller in capacity than countertop models; most have an interior capacity of 1.5 to 1.7 cubic feet. Larger capacities allow you to use larger cookware when microwaving.

  • Size: An OTR microwave's height is generally about 16 inches, which is ideal for mounting beneath a short upper wall cabinet. There are also slimline versions that are shorter and are ideal for certain kitchen configurations. There are also taller versions, which are normally reserved for convection microwaves, where taller cooking utensils are used. Most OTR microwaves are 30 inches wide to match the most common cooktop widths; there are also models as narrow as 22 inches.

  • Exhaust fan volume (cfm): The exhaust fan on a vented OTR microwave is rated in cubic feet per minute, or cfm, a measurement of how much air the fan can move. Kitchen designers suggest that any vent fan be rated for at least 100 cfm for each linear foot of range top but no more than 400 cfm. If you can find a 400-cfm unit that matches your needs and budget, this is the best choice.

  • Wattage: Microwave ovens are rated according to their operating wattage. OTR models generally fall between 900 and 1,000 watts. The higher the wattage, the quicker the appliance will cook foods.

In addition to these important basics, there are other convenience features to consider:

  • Program/shortcut settings: More sophisticated microwaves have more automatic settings to simplify common cooking tasks.

  • Finish: As with countertop microwaves, OTR units offer a choice of several cabinet finishes: white, black, stainless steel, black or brushed stainless steel, etc.

  • Sensors or probes: A microwave can have sensors that measure steam being emitted from foods or probes that measure interior temperature. These features allow the oven to shut off power to prevent overcooking.

  • Touchpad location: Some OTR microwaves place the touchpad controls along the bottom of the cabinet, which can be helpful to shorter users.

  • Turntables and racks: Some microwaves are bare interior cabinets, while others come with rotating turntables or interior racks.

Carefully consider how you cook and then buy an OTR microwave that includes the features you will actually use. It generally doesn't make sense to pay for features you will never need.

Installing an Over-the-Range Microwave

The installation procedures for OTR microwaves vary from manufacturer to manufacturer, but several major brands follow this basic procedure. This example assumes the over-the-range microwave will be mounted beneath a short upper wall cabinet that conceals the ductwork — the most common scenario. If you have a different configuration, consult the instructions for information on how to adapt the installation.

Step 1: Verify Over-the-Range Microwave Dimensions

Review the specifications for your over-the-range microwave oven and make sure it will fit in the space available. An OTR microwave must be installed so the top edge of the microwave is at least 66 inches above the floor and the bottom edge is at least 30 inches above the cooking surface. The width of the cabinet should be equal to or slightly less than the width of the cabinet above the microwave. The adjacent wall cabinets and top cabinet should be 12 to 14 inches deep.

Step 2: Plan the Duct Route

Before beginning installation, plan the route for the ductwork. The airflow will be most efficient with the shortest, most direct route, so when possible, plan to route the ductwork directly through the kitchen's sidewall behind the cabinet above the microwave. Where this is not possible, such as when the range and OTR microwave are positioned on an island or peninsula, strive for a route that is as short and straight as possible.

Check walls and ceiling spaces for the presence of wires or pipes that could interfere with the routing of the ductwork. It's better to have your ductwork route carefully planned before you begin.

Step 3: Run the Electrical Circuit

Most typically, OTR microwave ovens are powered by a dedicated 20-amp electrical circuit with a receptacle outlet placed inside the upper wall cabinet above the microwave oven. The outlet can also be located elsewhere, but it must be accessible so that the appliance can be easily unplugged for service.

Electrical codes in most communities now require that the microwave have its own dedicated circuit; it cannot be shared by other outlets or appliances. Adding a new circuit is normally done by a professional electrician, although skilled DIYers can do the work provided the installation is inspected. Complete this work before beginning installation of the microwave, and make sure the outlet is within reach of the microwave's electrical cord.

Step 4: Configure the Over-the-Range Microwave's Vent Outlet

Before beginning installation, make sure the microwave's vent outlet matches your situation. The procedure for directing the vent outlet varies considerably from manufacturer to manufacturer, but it normally involves adjusting the duct outlet to a direction that matches your ductwork — upward or toward the back of the microwave. If you are using round ductwork, you may need to attach a duct adapter that transitions the rectangular outlet to a round duct.

Image Credit: Paul Anderson

Step 5: Attach the Templates

In most installations, the microwave will hang from its back lower edge on a mounting plate anchored to the wall and from the top using bolts that extend down from the inside of the upper cabinet into the microwave's frame. To simplify this process, templates are provided, and they are taped to the wall behind the microwave and to the bottom of the cabinet above the microwave. These templates will guide you when drilling holes in the cabinet and when attaching the mounting plate to the wall.

Tape the templates in place as directed by the manufacturer. With some microwave ovens, the templates are printed on the appliance carton, so make sure not to damage the carton when uncrating the microwave. Mark the hole locations on the wall and the bottom of the wall cabinet, remove the templates and drill holes at the marked locations on the wall and cabinet.

Step 6: Attach the Mounting Plate

Next, attach the microwave oven's mounting plate to the wall. The mounting plate and attachment method varies depending on the manufacturer, but generally, it must be anchored to a least one wall stud as well as with two or more toggle bolts where there are no studs. The toggle bolt connections will require that you drill holes in the wall in order to insert the expandable wings of the bolts through the wall. Make sure that the mounting plate is installed perfectly level.

Step 7: Install the Vent Cap

Install the appropriate vent cap, which will terminate the ductwork to the outdoors. This can be a wall cap if the ductwork will terminate through a side wall (the preferred method) or a roof cap if the ductwork will terminate through the roof. This requires cutting a round or rectangular hole through the siding and sheathing or through the roof to insert the tailpiece of the vent cap from the outside.

Make sure to seal the vent cap with caulk or roofing cement to prevent leaking around the edges. A roof vent cap must be integrated with the shingles (or other roofing material) so water sheds over the flange of the cap.

Step 8: Run the Ductwork

Run lengths of approved, smooth-walled metal ductwork from the tailpiece of the vent cap to the location where the microwave oven's vent outlet will be located. Approved ductwork can be round or rectangular depending on where the ductwork is installed. Bends in the ductwork are formed with elbow fittings. Secure the joints between ductwork pieces and elbows using sheet-metal screws and metal-faced tape (not fabric duct tape).

Step 9: Install the Over-the-Range Microwave Oven

Hanging the microwave oven generally requires two people. Holding the microwave up near its final position, feed the power cord up into the cabinet. Then, hook the lower back edge of the microwave onto the mounting plate. Rotate the microwave so the top surface is flush against the cabinet. While one person holds the microwave in place, another person then screws mounting bolts down through the bottom floor of the cabinet and into the frame of the microwave oven.

Step 10: Connect the Ductwork to the Microwave

Connect the ductwork to the vent outlet on the microwave using sheet-metal screws and metal-faced tape. If the ductwork is round, this may require installing a transition fitting to convert the rectangular outlet to a round fitting. With some microwave ovens, it may be easiest to install this transition fitting before lifting the microwave into position.

Step 11: Test the Microwave Oven

Plug the microwave into the wall outlet and then test all functions, including the exhaust fan and task lights.

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Bryan Trandem is an avid home improvement DIYer and trained Master Gardener. He has been writing and editing books and articles on gardening, home improvement, woodworking, and home decor for more than 30 years. He lives in Minneapolis, MN.

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