Installing an Over-the-Range Microwave Oven

by Michael Chotiner
(Technical diagrams courtesy Whirlpool Corporation)

Like all disruptive technologies, microwave cooking is controversial. Most people don't really understand how microwaves work or how to use all of their available features. An estimated 90% of families in the U.S. use microwaves to cook and/or reheat foods, yet this handy appliance continues to take flak from chefs and foodies.

I can speak to some other contentious issues with authority: Many folks want built-in microwaves rather than freestanding models, to save usable counter space, but installers complain that the available sizes of microwave ovens don't really correspond to the typical dimensions of stock cabinets and other objects that must be coordinated in kitchen layouts, so it's often difficult to line things up for seamless visual effect without filler panels and other contrivances.

Size Matters!

Microwave ovens designed for use by consumers are available in three size classes: Compact, Mid-size and Full Size.

While the size of a microwave oven expressed in cubic feet gives you an idea of whether it's too small for much more than heating up a cup of coffee or large enough to roast a turkey, it tells you nothing about the overall width, height and depth of the appliance -- important to know if you're planning to build-in. Pro installers complain that many spec sheets purporting to give the overall dimensions do so inaccurately. I know one contractor who won't start to build a microwave cabinet until he has the actual unit in hand.

If you look at all of the available variants of microwave ovens on the market in terms of width, height and depth, you'll see that there really are no standard sizes, but microwaves designed for over-the-range installation all fit into a 30-in. wide space.

The Over-The-Range Microwave Option

Purpose-made microwaves are available with handy kits for installing them over a range, but OTR installations aren't always simple. Here are some issues to consider:

Ventilation: All microwave ovens have a built-in blower for a recirculating venting system. Most microwaves designed for over-the-range installation offer two more options for venting to the outdoors: The blower can be positioned to direct exhaust air up and out through the roof via ductwork above the unit or horizontally through ductwork in the wall behind the unit. While microwaves themselves don't need venting to the outdoors, when they're installed over a range or cooktop, vents for carrying odors, moisture and grease from conventional cooking out through the roof or an exterior wall should be provided, if possible.

Installed height: For safety and convenience, you don't want to install an OTR microwave too high. The National Kitchen and Bath Association says that the bottom of the microwave to be no higher than 54 inches off the floor. If anyone likely to use the microwave is shorter than, say 5'4", even the recommended standard might be uncomfortably high.

Clearance between stovetop and bottom of microwave: Building codes and other standards are inconsistent on the allowed clearance between a stove top and anything above it. At least one existing rule allows a minimum of 13 inches, but pro installers and others who know their way around kitchens argue that there should be 20 to 24 inches of clearance above the stove top.

(A note from NH:  I received a note on this height issue from a reader so some clarification is necessary.  Both height locations are general recommendations.

The height above the floor is to accommodate people of various heights to be able to comfortably use the microwave and read the display. The distance above the range top is 1) to allow for the widest range of kitchen pots and pans and also to allow full visibility of the range top to all but the tallest people and 2) to accommodate the normal distance that the manufacturer recommends.

There is some variability... taller people might want the microwave installed higher! Of course, the top cabinet may need to be modified or replaced in any installation if the microwave needs to be moved higher. I think the author may have been trying to cover all bases, but in any installation I have done the first order of business is to use the manufacturer's recommendations as to the MINIMUM distance to the cooktop. This protects the microwave from excessive heat which could be an issue with some models if mounted too close to the range.

I don't know for sure, but the manufacturer's height recommendation might also include an optimal height for the exhaust fan to have the most effect, though admittedly above the range microwave fans in general are not as good as a strong range hood!)

Preparation for installation

Long story short: To install an over-the-range microwave oven, you need to have enough space between wall cabinets flanking the range and between the cooktop and ceiling. There should be a cabinet or shelf above the spot where the microwave will be installed so that you can fasten the top of the microwave to it. Most OTR microwaves are just under 30 in. wide; heights vary from about 10 to 18 inches and depths vary from 12 to about 18 inches. You need to choose a model that allows adequate clearance above the range but can be installed at a comfortable height.

• Determine that the space between wall cabinets flanking the range is at least 30 inches. If the space is wider, determine about how you'll fill the space between the sides of the installed microwave and the flanking cabinets. Some OTR microwave kits include filler strips, or you can order filler panels that match your cabinets from the manufacturer or a cabinet shop.
• If a wall cabinet is present above the range, measure the distance between the top of the range and the bottom of the cabinet. Subtract 20 inches (or whatever minimum between the microwave and cooktop suits you) from that distance to determine the overall height of a microwave that will fit. You may find that you'll need to cut down the wall cabinet or install another of suitable height before starting the microwave installation.
• If a vented range hood is present, turn off power to the circuit by flipping the breaker, and disconnect the blower wiring. Remove the hood and determine if a suitable outlet into which you can plug the installed OTR microwave is present nearby. If not, have a professional electrician install one.

How to Install an Over-the Range Microwave Oven

All OTR microwave kits come with detailed instructions. Read them before starting your installation. Most manufacturers include templates in the package. You'll need these to lay out the holes that need to be bored in the wall behind the microwave and in the wall cabinet above for fasteners. In other cases there's a wall plate attached to the back of the microwave that must be unscrewed from the machine and held up against the back wall to so you can mark the fastener layout.

1. Find and mark the position of at least one stud in the wall behind where the microwave will be installed.
You can try using a stud finder (I've never had much luck with them), or look for fasteners inside the wall cabinets and measure in 16-inch increments over toward the wall where the microwave will be mounted. Wall studs are usually spaced 16 inches on-center, so you should be able to project the stud positions. Don't be afraid to probe around with your drill to make sure that you find something solid.

Example of a wall-mounted support plate for an
over-the-range microwave installation.

2. Hold the microwave wall template in position against the wall and mark the positions of the required fasteners.
At least one of those fasteners must go into a stud; where no stud is present, drill holes for toggle bolts. Fasten the back plate to the wall and check it for level and plumb.

Typical template for marking fastener locations
and cutouts on the cabinet above a microwave.

3. Position the template for the fasteners that will join the top of the microwave to the bottom shelf of the cabinet above it and make your marks.
That template should also help you lay out the position of the opening that will need to be cut for the exhaust damper and for the microwave power cord, which will most likely plug into an outlet inside of that cabinet. Drill the holes and make other cutouts as needed, according to the manufacturer's instructions.

4. Following the manufacturer's instructions, orient the blower for roof, through-the-wall or recirculating venting as needed.

With the bottom back edge engaged in the wall support plate,
the microwave is rotated upward to bring the top of the housing up
to meet the bottom of the wall cabinet above.

The power cord is threaded through the bottom of the cabinet
to bring it to a grounded outlet inside. Bolts through the bottom shelf
must be threaded through pre-drilled holes into mounting holes
in the top of the microwave.

With a helper, lift the microwave into its approximate position. Thread the power cord through holes in the cabinets, as needed, so it can ultimately be plugged into its receptacle. Trying not to strain or snag the power cord, tilt the microwave so you can engage the bottom back edge with the retaining strip on the wall plate. Then rotate the front end upward to get the top of the microwave tight against the bottom of the upper cabinet. With the helper supporting, thread the bolts provided in the kit through the holes you've pre-drilled in the bottom shelf of the cabinet and into the mounting holes in the top of the microwave. Use all of the fasteners recommended by the manufacturer and check the installed unit for level and plumb.

Ductwork for outside venting can be connected to
the microwave's blower/damper and concealed inside the cabinet.

Options for venting over-the-range microwaves to the outdoors
include through-the-roof and through-the-wall ductwork assemblies.

5.Connect the blower/damper assembly to the ductwork with the appropriate fitting -- usually a 3-1/4-in. X 10-in. rectangular-to-round transition.

Plug 'Er in and heat up a cup of coffee, or soften a pint of your favorite ice cream and eat it all up. You will have earned it. Now enjoy having a microwave that's out of the way yet entirely convenient.

About the author:  Michael Chotiner is an expert on appliance installation, and writes on his experiences for Home Depot. Michael's appliance installation tips for microwave ovens are based on his years as a general contractor. Home Depot's selection of microwave ovens, including models mentioned by Michael, can be viewed on its website.