How to Insulate the Outside Vent on a Microwave


Built-in microwavevens often have venting systems to draw food odors out of the home. The vent in the microwave runs outside via a hole in the wall. Properly insulating the area around this hole is critical to maintaining the energy efficiency of your home. The added insulation prevents cold air from seeping into the vent or walls, and thus into your home. The process requires accessing the wall space behind the microwave.

Things You'll Need

  • Screwdriver or power drill
  • Hand-held rotary tool
  • High-temperature silicone caulk or expandable spray foam
  • Dust mask
  • Safety glasses
  • Work gloves
  • Loose fiberglass insulation
  • Plywood (optional)
  • Wood screws (optional)
  • Open the cabinets above the microwave and locate the two long screws that penetrate through it and hold the microwave in place. Remove each screw using a power drill, then unplug the microwave’s power cord from the outlet. Grasp the sides of the microwave and carefully pull it out from the wall.

  • Remove the microwave’s mounting bracket from the wall by detaching all screws using a power drill. Set the bracket and the screws safely aside.

  • Remove the access wall panel, if applicable, by detaching the screws and lifting it away from the wall. If no panel exists, cut through the wall using a drywall knife or hand-held rotary tool, forming a rectangular shape. Only cut deep enough to penetrate the wall material. Lift out the wall panel to reveal the inside of the wall.

  • Peer into the rear wall cavity and locate the perimeter of the outside vent pipe. Apply a bead of high-temperature silicone caulk around the rim of the vent where it meets the home to insulate it from air and water penetration. If desired, you can apply expandable spray foam instead of caulk.

  • Scoop up a handful of the fiberglass insulation, pulling it apart slightly if needed. Stuff the insulation into the area behind the microwave at the location of the outside vent. Continue adding more insulation until no air gaps remain. Do not pack the insulation in tightly, since loose insulation protects better against the cold temperatures.

  • Reinstall the microwave by reversing the steps taken to uninstall it.

Tips & Warnings

  • If you did not have an access panel, cut a piece of plywood to recover the hole and secure it to the wall studs with wood screws. After installing the plywood panel, proceed with reinstalling the microwave.
  • Wear work gloves, a dust mask and safety glasses to protect from irritation caused by the fiberglass insulation particles.

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