Typically there might be a cabinet installed over the microwave and inside that cabinet will be duct work or a soffit above the microwave or a direct wall exhaust.
Can all over the range microwaves vent outside.
Remove the access plate on the top of the unit in order to reach the motor.
If rectangular ducting please note.
In the first example the microwave over the range otr will vent through the manufacturer installed grease or carbon filter then directly through an exhaust port that is ducted to the outside of the structure.
All over the range spacemaker microwaves can be vented to the outside using an equivalent total of 140 feet of rigid 3 1 4 x 10 rectangular or rigid 6 round ducting.
Over the range microwaves have a light and fan built into the bottom of the appliance.
For this reason vent ducts are the only choice.
Ultimately the goal of the vent is to pull the air from the microwave and deposit it to the outside.
When considering venting in an over the range microwave there are ducted vents and recirculating vents.
When a microwave is replacing a standard range hood it is usually best to use the existing venting method.
Microwaves are shipped from the factory to vent out the top vertically but can also be vented out the rear horizontally.
Microwaves over the range otr typically vent in two different ways.
Microwaves that vent to the outside force the air through duct work to the outdoors.
This eliminates smoke cooking odors moisture and hot air from remaining in the kitchen.
If you have an over the range microwave it should have an exhaust fan that vents to the outdoors.