Most over-the-range microwaves require precise placement to ensure both appliances work efficiently without damaging one another. Placing the microwave too close to the cook top can cause either appliance to work inefficiently and it may be a fire hazard. Consult your microwave installation instructions to determine the placement requirements.
Venting a microwave and an oven is vital to ensure that the appliances and the kitchen remain dry. Failing to vent the microwave and oven can cause a puddle to form in the oven, encourage mold growth and even become a fire hazard. Many over the range microwaves have vents on the bottom that allow you to vent the oven through the microwave. You can vent the microwave through a vent on the top or through a ventilation pipe that goes through cabinetry.
Microwaves can be quite heavy. Keep them firmly attached to the wall by anchoring a steel mounting plate directly to your wall studs. Find the studs with a stud finding tool or by gently tapping the studs until you hear a dull thud. Most microwaves require you to attach at least one wall stud. The mounting plate has several holes in it that allow you to attach the microwave to the plate through the inside of the top of the microwave.
Most over the range microwaves are either 30 or 36 inches wide. Cabinets that you purchase from a box store will also have either a 30- or a 36-inch cavity for the microwave. Cabinet fillers allow you to hide the gaps in between the microwave and the cabinets. These fillers can either match the cabinet or the microwave. In some cases, the microwave will vent through these gaps.