how to install an over the range microwave

Something I wish we would have done when we first installed our kitchen was to properly vent our over-the-range microwave. Our microwave was just recirculating the air back into the kitchen. So bacon or anything I cooked was just staying in the air. Installing vent ducting to an outside wall will force the air outside removing cooking odors, smoke, moisture, and heat.

Our kitchen was in desperate need of some venting. We have a microwave above our stove on an outside wall, so our objective was to install vent ducting that connects to the microwave exhaust fan port and moves the air outside.

Here's how we installed vent ducting to our over-the-range microwave.

List of tools and supplies we used:

Universal Exhaust Kit (we bought it but didn't use it)
Tape measure
Pencil
Straight edge
Reciprocating saw
Oscillating saw
Utility knife
Duct tape (Use HVAC foil tape)
Exterior vent
Short Way 90 Degree Rectangular Elbow
Rectangular Stack Duct Starting Collar
Metal shears
Eye protection
Shop vac

Here's How to Vent an Over-the-Range Microwave on an Outside Wall.

We bought a Universal Exhaust Kit but discovered once we got into the project that it wouldn't work very well for us. The piece that came with the kit wasn't flat on the backside and didn't allow for enough clearance between the microwave exhaust port and the back wall. Luckily, we had the correct pieces already. The rectangular elbow piece aka the Short Way 90 Degree Rectangular Elbow worked much better for the layout we have.

The rectangular elbow came with cut corners so we flattened the edges out, creating a flange to make it easier to fit.

With our pieces all ready to go we then marked out where we needed to cut the hole on the back wall. Always measure twice to cut once.

Cut Hole for Vent

With the oscillating saw, Kenney cut the hole on the back wall removing the sheetrock. He then used the utility knife to remove the plastic layer and insulation. Before doing this make sure to cover up the microwave and stove. It also helps to follow the saw with the shop vac to keep the mess to a minimum. (That was my job).

The following hopefully won't be your situation, but we had a stud in the way of the hole we needed to cut. Half of the stud was in the hole opening, so the solution was to cut a 'dado' in the stud. A dado is basically a channel that runs across the grain of the wood. To cut a dado, make marks with your pencil on the stud and cut with a reciprocating saw across the marked top part of the stud and through the marked bottom part of the stud to the desired depth and or width. Then you take a hammer and chisel and remove the waste.

Since Kenney is a former carpenter, he did this his own way. He brought out the battery chain saw. And with the tip of the saw, he bored through the stud with the precision of a surgeon and with the style of Mad Max. (Definitely not recommended for an amateur.)

Needless to say this made a total mess of my stove, my kitchen counters, and floor, because, of course, we didn't think to cover everything up first. Shop vac to the rescue!

This chainsaw plunge cut he did went all the way through the exterior wall of the house. Then it was just a matter of squaring the hole on the exterior of the wall with the reciprocating saw and the oscillating saw. BUT that's how we did it and not something we recommend at all.

Instead, to make the outside wall cut, you can mark the outline with a pencil on the interior back wall and drill through each of the 4 corners using an 8″ or 10″ long 1/4″drill bit. Make sure when you drill that you're straight, level, and square to the wall (as if your body was a drill press). Then on the exterior, cut the hole with an oscillating saw or small circular saw.

Assemble Vent Ducting

Before final assembly he had to trim part of the flat edge of the elbow to get it to fit properly. To trim the flange use a straight edge and draw a straight line. Then just use metal shears (or as I call them 'the giant scissors that cut metal) to cut across the line.

Now it's time to put it all together. He took the Rectangular Stack Duct Starting Collar and inserted it into the U channel of the rectangular elbow. The elbow was then fit on to the microwave exhaust. The duct collar was inserted in the hole in the wall and everything was sealed up with duct tape. Imagine that! We actually used duct tape for duct work! Actually, we recommend you use hvac tape. It's duct tapes bigger brother and will provide a much better bond. But since we'll be re-configuring this area eventually we used duct tape.

The exterior vent was then finally inserted through the exterior wall into the connecting duct pipe (which was connected to the elbow, which was connected to the microwave).

Seal Vent Ducting

There are 2 ways to do the sealing — permanent and temporary.

Permanent: Insert exterior vent tube partially into connecting duct tube. Make 2 to 3 rows of silicone beads all the way around the vent tube. Continue sliding the vent tub through the duct and screw to the wall. The silicone will smear itself creating a permanent seal between the vent tube and the wall duct.

Temporary: (If you're planning to remodel like we are). Insert duct all the way, put temporary mounting screws to hold vent in place. Remove vent screen and while reaching into the vent itself take care not to damage the vent flap. Make small lengths of ducting tape and reach inside the vent duct and tape the seam between the vent collar and exterior vent tube all the way around the inside of the duct. And then replace the vent screen.

All done now! But before we could relax we checked to make sure the fan worked. To check the air flow, you can light a candle and hold it under the microwave with the fan on and blow the candle out. The smoke should disappear.

Our fan works like a charm! Now I can cook without setting off the smoke alarms! Bacon anyone?