In this video, This Old House general contractor Tom Silva shows how to install a wall-mounted microwave oven with ducted fan hood.
1. Use the manufacturer's template to mark cutout lines onto the wall.
2. Cut through the drywall using an oscillating multi-tool.
3. Pull the insulation from within the hole.
4. If there's a wall stud in the way, enlarge the hole in the drywall and cut out the stud with the oscillating multi-tool.
5. Reframe the opening using 2x4s; install a bottom plate, header, jack studs and blocking. Secure the new framing to the old framing with 3-inch screws.
6. Fill in voids within the new framing with fiberglass insulation.
7. Screw a ½-inch plywood panel over the new framing.
8. Screw the oven's mounting bracket to the plywood panel and framing.
9. Drill holes through the house wall from the inside.
10. From outside, cut through the siding using a right-angle grinder or oscillating multi-tool.
11. Cut through the plywood house sheathing using a reciprocating saw.
12. Spray expanding foam insulation around the inside of the wall hole.
13. Set microwave oven onto the bracket, then screw down through the upper cabinet and into the top of the microwave.
14. Apply silicone sealant around flange of the vent hood, then slide it into the hole and screw it to the house siding.