How to Install an Over-the-Range Microwave

Updated on September 29, 2017
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Dan has been a homeowner for some 40 years and has nearly always done his own repair and improvement tasks. He is a licensed electrician.

Installing an Over the Range Microwave

Most of the time, installing an over the range microwave oven is not difficult, but each house is different, and problems can be encountered. This article is designed to cover some of the potential problems that may be found as well as give basic instructions on how to install an over the range microwave oven.

The descriptions and photos are from the third such over the range microwave oven I've installed in recent months, with the work being done this time in an older home. Older homes often present the most problems, from electrical to cabinetry, and some of those problems and the solutions to them are presented here.

Even with the problems encountered, the task of installing the over the range microwave was not difficult and took about two hours to accomplish. All three of the units I've installed came with good descriptive instructions, and all three were very similar in installation procedures. The work is well within the capabilities of most homeowners.

Click thumbnail to view full-size
The range fan above the range must be removed.Checking the power - this wire is hot and must be shut off at the circuit breaker.  The lower area with silver tape is the "up" side of the old fan.Wires are fished up from the old hole below the cabinet into the new square hole cut into the back of the cabinet.   Note the white colored wire running through the space inside the wall.  It would be easy to damage this wire.Electrical box installed and the wires hooked properly to the new receptacle. The new receptacle is installed.  The newly installed microwave is plugged into it.  The new microwave even supplied a clip to "clean up" the wire in the cabinet.
The range fan above the range must be removed.
The range fan above the range must be removed. | Source
Checking the power - this wire is hot and must be shut off at the circuit breaker.  The lower area with silver tape is the "up" side of the old fan.
Checking the power - this wire is hot and must be shut off at the circuit breaker. The lower area with silver tape is the "up" side of the old fan. | Source
Wires are fished up from the old hole below the cabinet into the new square hole cut into the back of the cabinet.   Note the white colored wire running through the space inside the wall.  It would be easy to damage this wire.
Wires are fished up from the old hole below the cabinet into the new square hole cut into the back of the cabinet. Note the white colored wire running through the space inside the wall. It would be easy to damage this wire. | Source
Electrical box installed and the wires hooked properly to the new receptacle.
Electrical box installed and the wires hooked properly to the new receptacle. | Source
The new receptacle is installed.  The newly installed microwave is plugged into it.  The new microwave even supplied a clip to "clean up" the wire in the cabinet.
The new receptacle is installed. The newly installed microwave is plugged into it. The new microwave even supplied a clip to "clean up" the wire in the cabinet. | Source

Incomplete or Missing Electrical Connections

The task began with the removal of the old range fan unit, mounted in the place the over the range microwave oven was to occupy. The home I worked in is about 40 years old, and construction methods were somewhat different then. Although the normal 30" wide microwave fit easily into the space provided by the range and cabinetry and the necessary 30" clearance from the bottom of the microwave to the range was more than adequate it didn't take long to find that there was no reasonable power source for installing the new microwave oven.

The old house had the range fan hardwired, without a plug in for the microwave, and while it is possible to wire the new microwave during the installation process it is not the optimal solution. In such cases the power for the range fan simply pokes through the wall behind the fan, is run into the fan and hooked up. A new receptacle is needed in the cabinet above. Turn the power off before continuing any further! The best method to make sure the power is off is to use a non-contact voltage detector, but the fan light could be turned on and the breakers turned off until the light goes off. What ever method is used, make sure the power is off before disconnecting the fan.

The area where the power cable comes through the wall will be hidden by the microwave, so even fairly large holes in the wall won't be of any particular concern. I found that the hole where the wire came through wall was quite large, perhaps 2" X 4" - plenty large enough to work through, and the wire was easily long enough to run higher, inside the wall, and exit through the back of the cabinet just above. It only needed to go up a few inches, and there was plenty of wire to do that.

A new hole was cut through the back of the cabinet just large enough for a "old work" electrical box, and the wire easily fished into that hole. Before cutting the hole, the general area where the plug was to go was investigated from the original hole below, and I found that there were two other wires in the area. The plan had been to cut the hole through the cabinet and sheetrock wall behind it with a sabre saw, but that would probably cut the wires buried in the wall, so a sheetrock saw was very carefully used to cut the hole. A little more work, but it prevented damaging the wires behind the wall.

If you are not familiar with the installation or wiring of outlets, instructions are available in the link here; be sure to read and understand them. In particular, make sure the power is turned off before any work is done.

With the new plug in installed and the fan removed, the work of actually installing the over the range microwave was ready to proceed.

Installing the microwave supports

Click thumbnail to view full-size
The mounting bracket is installed.  The large hole in the back is for the fan exhaust, and was already there.The long screws are placed in the holes in the cabinet bottom, although will have to be slipped out to install the microwave.  The larger hole for the cord is further back.Template for holes in upper cabinet.
The mounting bracket is installed.  The large hole in the back is for the fan exhaust, and was already there.
The mounting bracket is installed. The large hole in the back is for the fan exhaust, and was already there. | Source
The long screws are placed in the holes in the cabinet bottom, although will have to be slipped out to install the microwave.  The larger hole for the cord is further back.
The long screws are placed in the holes in the cabinet bottom, although will have to be slipped out to install the microwave. The larger hole for the cord is further back. | Source
Template for holes in upper cabinet.
Template for holes in upper cabinet. | Source

Installing the Microwave

The first step in installing the new microwave is to attach the mounting bracket to the wall. The exact center of the area is measured (in my case 15 1/16" from each side) and a line drawn down the wall. The bracket is centered on the line and attached to the wall.

Attachment is accomplished by either using toggle bolts or wood screws. The instructions indicated that at least one wood screw is to be used, so the studs must be located for that screw, as well as any others that might be used. In the case here, the studs were visible through either the exhaust vent hole or the smaller hole where the wire originally came through the wall, but in most cases a stud finder from your homeowners tool set is very useful.

In my case there were wooden blocks installed on the underside of the cabinet to support the fan, and these blocks extended from the front to the back under the cabinet. The blocks resulted in the bracket being installed just barely too high and it had to shifted just slightly down by loosening the screws and pushing down. The instructions indicate that the bracket should touch the bottom of the cabinet; I suggest that it be installed perhaps 1/16" or 1/32" lower down. It will make installation of the microwave easier if this bracket is just below the cabinet instead of touching it.

Holes need to be drilled through the wall for the toggle bolts; 5/8" is the perfect size for most toggle bolts, and a spade bit makes quick work of the sheetrock. The stud(s) to receive wood screws should also be predrilled as the large screws may split the wood and are difficult to drive without predrilling the 1/16" hole recommended. In my case, I found an additional stud that could be used and so used 3 toggle bolts and 2 wood screws instead of the 3 toggle bolts and 1 wood screw. It doesn't affect the installation of the oven and provides a more secure support.

The cabinet bottom needs prepared as well; holes must be drilled in exact locations for screws to pass through and screw into the microwave. A paper template is provided to locate these holes; tape it to the bottom of the cabinet and drill where indicated. Holes that are 3/8" in diameter are the preferred size for the screws, while a 1 3/8" spade bit provided the hole necessary for the electrical cord to pass through that was just right for that cord end. The instructions indicated a 2" hole for the cord, but that is overly large; the smaller 1 3/8" hole was perfect.

The sides of the cabinet generally project down past the bottom of the cabinet, and in this case a wooden block needs to be made so that when it is placed under the cabinet it is the same height as the sides are. The installed microwave will touch the bottom at the lowest point (i.e. the protruding cabinet sides) and the screws will deform the top of the microwave as they are tightened if there is no surface to stop the sheet metal of the microwave from being drawn up. Drill the same 3/8" hole in the blocks so the screw will pass through the bottom of the cabinet and the block into the microwave. In my own case the block needed to be 1 1/4" thick; a typical ¾" pieced of wood coupled with a piece of ½" plywood would have been perfect, but blocks were already in place to support the now removed fan.

Unfortunately the holes in the bottom of the cabinet and the blocks were almost, but not quite, in the correct spot. And additional 1/2 hole needed to be drilled; this was done by working the drill bit up and down with side pressure applied until the holes were in the correct place, but elongated. The screw head nearly fell through the elongated hole, which is of course unacceptable. I chose to use some large "fender" washers on top to cover the hole; these washers are over an inch across with only a 1/4" hole for the screw to go through and thus covered the overly large hole in the cabinet bottom and spread the weight out. Alternatively, a new false bottom could be placed in the cabinet, made from hardboard.

Adjusting the blower motor

Click thumbnail to view full-size
Closed off exhaust holes in back of the microwave.The exhaust path is now opened correctly for rear exhaust.  Vertical exhaust is also a possibility.
Closed off exhaust holes in back of the microwave.
Closed off exhaust holes in back of the microwave. | Source
The exhaust path is now opened correctly for rear exhaust.  Vertical exhaust is also a possibility.
The exhaust path is now opened correctly for rear exhaust. Vertical exhaust is also a possibility. | Source

Adjusting the blower

As it came from the factory, the exhaust blower in the microwave was installed to recirculate air back into the room. The duct work to exhaust it outside was already in the wall, so it only made sense to use that duct, which the microwave is designed to do with a little modification. The photo shows how the exhaust area in the microwave is closed off from the factory; the blower assembly is removed from the microwave, turned to the orientation shown in the second photo and reinstalled. It sounds much more complicated than it is; the entire procedure took less than five minutes and was very easy.

The duct in the old house was not in real good condition and was considerably larger than the exhaust from the microwave so foam insulation of the type used around doors or windows with a sticky side was used on the wall to seal the area. In this manner the back of the microwave is sealed against the wall except for the ducting, and air must go up the duct instead of around small cracks behind the installed microwave and back into the room. This can be seen in the photo above that also shows the bolts passing through the cabinet bottom. It is the gray area around the duct. The insulation on hand was wide, but quite thin at about ¼" thick, so two layers were used.

Installed over the counter microwave
Installed over the counter microwave

Installing the Microwave

The actual installation of the microwave is quite simple - the bottom rear of the microwave is set onto the small hooks on the rear bracket screwed to the wall, the plug and cord fed up inside the cabinet, and the unit tipped up into place. The long screws need to be placed through the holes in the bottom of the cabinet and screwed into the microwave and the cord plugged in. My unit had three screws into the top of the microwave, with a notation that the center one is not to be tightened too much.

In my case the grease screens needed to be installed into the bottom of the microwave and the glass turntable set into place. The clear plastic film over the keypad needed to be removed, and voila! the unit is ready for supper.

Most of the tools I used are common around the house, although I did use an impact driver for driving the wood screws. A cordless drill will work nearly as well, and even a screwdriver would do the job with a good deal of effort (the screws provided are quite large). Probably the biggest obstacle for most homeowners will be a lack of confidence, but you can learn to do most home repairs yourself - all it takes is a little time and a few of the right tools. My own experience in installing this particular over the range microwave would tend to indicate that they can be installed in virtually any home. At absolutele worst I would expect a new power line to have to be pulled from the circuit panel or nearby plug, and new ducting installed if there is none and the owner insists on an outside duct. On a scale of 1 - 10, this task rates about a 3. My total time, including mounting the new plug, cleaning up afterward and taking photos was about 2 hours.

Installing an over the range microwave

Questions & Answers

© 2010 Dan Harmon

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    • wilderness profile image
      Author

      Dan Harmon 5 months ago from Boise, Idaho

      Connie: You have two problems here. You are wanting to move the microwave only 1/4", to a 3" gap on both sides. It may be possible to slide it on the backing, but it may not, either, and require that the backing be moved that 1/4". It is unlikely that putting lag bolts (or large screws) just 1/4" from existing holes will give enough support, even assuming it wasn't put where it was in order to have studs to put the screws into.

      But beyond that, you will have to enlarge the screw holes in the cabinet above. If there are blocks used to support the microwave, they can be moved and the existing holes re-used, but it will require a larger hole in the cabinet itself. If there are no blocks used to distribute the weight in the cabinet you will have to supply some.

      Hope that helps.

    • profile image

      Connie Clawson 5 months ago

      My lg microwave was not centered correctly in a 36 nice space above my 30 inch stovetop causing a gap of 2 3/4 inch on one side and 3 1/4 gap on the other side. Was supposed to have a 3 inch cabinet filler on both sides. Can the microwave be slid over a little to accommodate this or will it have to be removed and reinstalled. And what about the toggle bolts.

    • wilderness profile image
      Author

      Dan Harmon 13 months ago from Boise, Idaho

      Interesting question. It must fasten behind and above, and to material strong enough to hold it up. One must be able to get inside any "bulkhead" above and provide strong supports, although the wall behind needs only something along the lines of sheetrock. Given those requirements can be met, though, it shouldn't be too difficult - at worst open up the structure above or construct something, and then cover the opening after adding structural support.

    • profile image

      P Donohue 13 months ago

      Any ideas on how to install oven top microwave if there isn't a cabinet but bulkhead instead?

    • wilderness profile image
      Author

      Dan Harmon 4 years ago from Boise, Idaho

      I have seen any that shallow. Amazon lists several at or just over 15" deep, but that's about it. I suspect it will be very hard to find (or impossible) because that will sit it quite a ways back from the front of the range and make it difficult to load and empty.

    • profile image

      thiele 4 years ago

      I have a questions/ any idea where I can get an over the stove microwave that is only 14" deep, thanks

    • wilderness profile image
      Author

      Dan Harmon 6 years ago from Boise, Idaho

      Coincidentally, I very recently did just that. The last microwave I installed lasted just one year and 5 days. Five days past the warranty period.

      A new one was purchased, of a different brand, and installed. The brackets were radically different - there was no chance that the old bracket would fit the new microwave.

      Even if I had purchased the same manufacturer, I doubt that the bracket would have fit. The same model - maybe, but even that is in doubt.

      Plan on removing and replacing that old bracket. If you don't have to, well and good, but you should be prepared to do so.

    • profile image

      amkjud 6 years ago

      if i am replacing an older microwave, will the hanging bracket be the same or will i need to replace it?

    • wilderness profile image
      Author

      Dan Harmon 6 years ago from Boise, Idaho

      Thanks for the vote of confidence; I try to give instructions for someone that has never done the task before.

    • saleheensblog profile image

      saleheensblog 7 years ago from Dhaka,Bangladesh

      useful info, voted up

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