How to Route Your Microwave Exhaust Vent to the Outside

Many times, you can convert an over-the-range microwave vent to exhaust to the outside.

A microwave is an essential appliance in most households, but installing one that vents to the outside can be a daunting task. However, with the right tools and knowledge, the installation process can be straightforward and stress-free. 

This article provides a step-by-step guide on how to route a microwave exhaust vent to the outside, or external venting, allowing you to upgrade your kitchen while keeping it safe and functional.

In This Article:

Closeup of steam rising from a stainless steel pot
No one wants the smell of last night’s cooking in the house today — not to mention the moisture, which can lead to mold and mildew. (©Adam, Adobe Stock Photos)

Why External Venting is Important

External venting is the process of directing air, moisture, and other pollutants to the outside of the house instead of recirculating them back into the kitchen. 

Here are a few reasons why external venting is important in a kitchen:

  1. Removal of Cooking Odors: Cooking odors such as smoke, grease, and other cooking fumes can quickly build up in the kitchen, causing an unpleasant odor. A proper external venting system removes cooking odors from the kitchen and directs them outside, ensuring that the kitchen smells fresh and clean.
  2. Moisture Control: Cooking food generates a significant amount of moisture, which can lead to mold growth and other hygiene issues if not adequately controlled. A venting system removes this excess moisture from the kitchen, preventing the buildup of humidity and moisture-related issues.
  3. Heat Control: Cooking also generates heat, which can be uncomfortable in the kitchen, particularly during the summer months. External venting helps to control the heat generated by cooking and directs it outside, keeping the kitchen cooler and more comfortable.
  4. Air Quality: A venting system helps to remove pollutants such as carbon monoxide and nitrogen dioxide from the kitchen, improving the overall air quality in the house. These pollutants can lead to respiratory issues and other health problems if not adequately controlled.
  5. Increased Appliance Lifespan: Appliances such as microwaves and range hoods that vent externally tend to last longer than those that are not. This is because venting helps to reduce the accumulation of moisture and cooking odors, which can cause damage to the appliance over time.

In conclusion, proper ventilation ensures that the kitchen remains fresh, comfortable, and safe for all who use it.

Over the range microwave in kitchen with an inside exhaust vent
Over-the-range microwaves typically have built-in exhaust fans that can be vented externally. (3 Echoes Content Studio)

Microwaves That Can Be Converted to External Ventilation

Not all microwaves can be converted to external ventilation. Before attempting to convert your microwave, check the manufacturer’s guidelines and specifications to ensure that the appliance is suitable for external venting.

Here are two types of microwaves that can be converted to external ventilation:

  • Over-the-Range Microwaves: Over-the-range microwaves are mounted above a range or cooktop. They typically have built-in exhaust fans and can be vented externally through a duct that runs through the wall or roof of the house.
  • Built-In Microwaves: Built-in microwaves are installed into cabinets or wall cavities. These microwaves can be vented externally through a duct that runs through the wall or roof of the house.

The process to convert a microwave vent to exhaust outside can be challenging, so you may want a professional to do it. It is crucial to follow the manufacturer’s guidelines and specifications and hire a qualified professional if you are unsure about the process.

Tools and Material Needed

Here is a list of the tools and materials needed to route a microwave exhaust vent to the outside:

  • Screwdriver
  • Pliers
  • Transition piece
  • Ductwork
  • Metallic tape
  • Laser measuring tool
  • Jigsaw
  • Roofing tacks and sealant
  • Cabinet-grade plywood
  • Corner trim
  • Primer and paint

Steps to Route a Microwave Exhaust Vent to the Outside

Note: It is important to follow safety guidelines and regulations when installing or modifying any electrical appliance. If you are unsure about any of the steps, consult with a professional contractor or electrician.

Interior Steps

Rotating the microwave motor

Turn off the power to the microwave by unplugging it or turning off the circuit breaker that supplies power to the unit.

Hands holding the access plate on top of a microwave
If the access plate is held in place by screws, use a screwdriver to remove them. If it’s held in place by clips, use a flathead screwdriver to carefully pry them off. (3 Echoes Content Studio)

Remove the access plate on the top of the unit in order to reach the motor. The access plate is usually held in place by screws or clips. If it’s held in place by screws, use a screwdriver to remove them. If it’s held in place by clips, use a flathead screwdriver to carefully pry them off.

Once you’ve removed the access plate, locate the motor mounting screws on the back of the microwave. Then, use a screwdriver to remove these screws, and carefully take out the motor.

Hands rotating a microwave motor
The direction of rotation can usually be found on the motor itself or in the microwave user manual. (3 Echoes Content Studio)

Next, rotate the motor 90 degrees so that the fan motor now blows upward. This directs the exhaust up and out of the microwave, so it can vent to the outside instead of back into the room. Once you’ve rotated it, reattach it to the microwave using the mounting screws you removed earlier.

Attach transition piece

Hands installing a transition piece on top of a microwave that will connect the exhaust vent to the outside
A transition piece is used to connect the microwave exhaust vent to the ductwork or hood above it. (3 Echoes Content Studio)

The next step is to attach the transition piece that will connect the microwave to the ductwork leading outside. Purchase a transition piece that matches the dimensions of the microwave exhaust vent and the ductwork or hood above it. Transition pieces are available in a variety of sizes and shapes, so be sure to choose the one that is appropriate for your needs.

Carefully align the transition piece with the exhaust opening on the back of the microwave, then use screws or clamps to secure it in place.

Attach ductwork

Cut the hole to the same dimensions as the transition piece. (3 Echoes Content Studio)

Using a jigsaw, cut a hole in the top and bottom of the cabinet so the duct can pass through.

To ensure that the hole in the ceiling is in the right location, use a laser measuring tool to mark a dot on the ceiling that identifies the center of the hole. This will make it easier to cut the hole accurately.

Metallic duct tape seals any gaps in the ductwork. (3 Echoes Content Studio)

Inside the cabinet, use metallic duct tape to seal the joints between the transition piece and the microwave. This prevents any air from escaping through the gaps.

Exterior Steps

Use a laser measuring tool to mark a dot on the roof decking that identifies the center of the hole. (3 Echoes Content Studio)

In the attic, mark a spot directly above the duct so you can cut a hole in the roof decking. Use a reciprocating saw or other saw to cut a hole in the roof decking that is the same size as the ductwork.

Use roofing sealant around the perimeter of the flange to prevent and leaks. (3 Echoes Content Studio)

On the roof, tuck the flange of a roof vent under the shingles above the opening and secure it with roofing tacks and roofing sealant. This will ensure the vent is securely in place and prevent any leaks.

Cabinet-grade plywood will give the frame a finished look. (3 Echoes Content Studio)

Finishing Touches

To hide the exposed duct in the kitchen, use wood studs to build a frame around the exposed duct. This will create a structure that you can attach the plywood to, and provide support for the cover.

Once the frame is in place, cover it with cabinet-grade plywood. This will create a clean, finished look and hide the ductwork from view.

To finish the cover, add corner trim to cover any exposed edges of the plywood. This will create a professional-looking finish that matches your kitchen decor.

Use the same color paint as the wall so the frame will blend in. (3 Echoes Content Studio)

Apply a coat of primer and two coats of wall paint to finish. This will give the frame a polished look and blend it into the rest of the kitchen.

Exhaust vent on a rooftop
A proper venting system will remove the air from the kitchen and prevent the buildup of moisture and odor. (3 Echoes Content Studio)

Testing the Microwave’s External Ventilation

After you’ve routed your microwave exhaust vent to the outside, it’s crucial to test it to ensure it’s functioning properly and venting outside correctly. Failure to properly test the microwave could lead to potential hazards such as carbon monoxide buildup, which can be deadly.

To test the microwave and make any necessary adjustments, follow these steps:

  1. Turn on the microwave and let it run for a few minutes. This will help to ensure the fan is working properly and the air is venting outside.
  2. Check the exhaust vent outside to make sure that air is flowing out properly. You should be able to feel the air coming out of the vent with your hand.
  3. If the exhaust vent is not working properly, check the ductwork for any obstructions or kinks. Remove these so the air can flow properly.
  4. If the ductwork is clear and the exhaust vent is still not working properly, check the fan motor to make sure that it is running properly. Replace the motor if it’s not running.
  5. Once you have made any necessary adjustments, retest the microwave to ensure that it is functioning properly.

Further Reading


  1. I want to replace an old OTR microwave. Due to the kitchen layout the microwave will be installed on an inside wall. I want to vent to the outside. The old microwave did not. It appears when this house was built provision was made for venting out the rear of the microwave into the standard 2×4 wall, up the cavity inside the wall, then up through duct work in the attic through the roof. I would like to use that path to vent a new microwave. My question – given the cavity would be only 3.5 inches deep plus 0.5 inches for the drywall (14. 5 inches stud to stud), will the damper that is attached to back of a typical microwave significantly block the upwards airflow when the fan pushes it open to exhaust the air? We haven’t purchase a new microwave yet so I am unable to see what the overall depth at the damper will be when pushed open. I do not have the option to vent through the cabinet above. Your advice would be appreciated.

  2. I have an interior wall range with microwave/hood. We wanted to have a replacement microwave/hood dropped lower by 1 1/2 inches and have it vented. Contractor said that venting would have to be through overhead cabinet and run on top of cabinet to external wall with hole punched to exhaust to side. Above the kitchen is a full bath adjoin closet bedroom, so I’m not sure if there is a direct pathway to roof above 2nd floor. Is this a good idea to have vent resting above kitchen cabinets to vent outside?

  3. In the video, you did not show how to connect the duct work to the transition piece or the roof vent. You just skipped over that and showed it as done. How do you do this? ( Showing how to put the cap vent under the shingles does not show how to attach the duct work underneath to it.)

  4. I need exactly what u had demoed in the video. Replace microwave with vent out. Do u have services in San antonio Texas and tentative/approx , what would be the cost to do this ?

    • Hi, Bob, features home improvement advice from the nationally syndicated TV show “Today’s Homeowner” and its experts.
      We don’t offer information on individual home builders, repairers and suppliers, but we encourage checking your local phone listings for this information and project estimates, which vary by location.
      Thanks for your question, and good luck!

    • Hi, Ginny,
      We can’t provide product recommendations due to the constantly changing inventory, but we recommend checking your local home center, asking questions and ensuring the product matches your needs.
      Good luck!

  5. My question is the same as Raymond’s. I need to vent through the wall. The vent was installed for an old microwave which now needs to be replaced. I guess the problem is to find a replacement designed to line up with what I have. Thanks for your advice.


  6. I bought a whirlpool microwave model vml75011HV-4. I had the installer vent it to the outside of my house. However, when I use the venting system it still blows air out inside my house as well as outside. Is this normal and should I have any air coming out of the front of my microwave into my kitchen?

  7. My microwave is installed on a wall adjacent to the garage. We have switched the MW from recirculating to venting and added the metal flange on the back. we have cut the drywall in the garage and now just need to add the proper vent piping or ductwork to get it to the side of the garage to cut an exterior vent with vent cap and bird screen (of course!). What is the proper size vent pipr or ductwork required in Virginia?

    • Hi, Steve,
      Great question! We have forwarded it to the Today’s Homeowner Radio Show’s producer.
      He will contact you soon to discuss featuring it during an upcoming show.
      Take care!


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