Many microwave ovens are not vented to the outside. If you are willing to give up the outside venting feature, you can have a service person from the appliance dealer turn the fan around to vent inside. Remove the wall jack and insulate and seal the wall opening.
The joints should be sealed, and if the duct runs through an unheated space, they need to be insulated. How do you seal a range hood duct? If the gaps are larger than 1”, they may be sealed from the attic side with air-blocking material like rigid foam that's cut to fit and sealed in place with caulk or spray foam.
There is no requirement that your Over The Range (OTR) Microwave be vented to the outdoors. All OTR microwave ovens can be set up to either allow the fan to recirculate the air back into the kitchen or be vented to the outdoors.
They do a better job of extracting toxins and smoke (although not at the same level as a range hood). A vented option will remove these fumes and vent them to the exterior of your home. A recirculating OTR microwave uses charcoal filters to neutralize air before it is pumped back into your kitchen.
A ductless recirculating vent pulls air through a filter and exhausts the air back into the kitchen. Some units are equipped with a charcoal filter that traps some particulate matter and odors, but most of the heat and moisture, along with some types of particles, stay in the house.
You can insulate your vent hood duct, but it's not required. Insulating your vent hood duct will keep the noise down and keep your greasy kitchen air from escaping into your joists and attic.
When insulating HVAC ductwork, use a foil, faced fiberglass insulation with an R-6 or higher R-value. Use the type of metallic foil duct tape recommended by the insulation manufacturer to seal and hold the insulation in place. Make sure the foil surface of the insulation is free of dust before applying the tape.
Can flexible duct be used for a range hood? No. Avoid flexible duct for your range hood, regardless of the CFM.
If you're comfortable with metal working, cover up your old range hood vent using sheets of galvanized metal—the same material used to install flashing along a chimney. Your home center will have sheets or rolls of metal, as well as specialty tin snips for cutting.
Microwaves cannot be ducted into a common duct work. DO NOT vent into an attic or crawl space.
This is an exhaust damper assembly for a microwave, which is also known as a microwave vent damper. The damper directs air flow through the vent duct from the top or rear of your microwave, depending on your model, to allow the air to flow outside and prevent outside air from coming in.
Stop vent clanging with dampers
Measure the diameter of the vent pipe and order the dampers from a duct supply company (hvacquick.com is one source). Start by replacing the backdraft damper directly above the vent hood. If that doesn't solve the problem, install a second damper near the wall or roof discharge cap.
Lower the front of the microwave and have a look over the top, under the cabinet. The unit will be supported at the lower rear by a bracket flange. Your microwave's vent either exhausts upward or rearward, but from right at the top rear of the unit. You'll be able to see whether there's a duct opening at that location.
Use a utility knife to cut foil-faced fiberglass insulation to the proper size. Wrap the insulation around the duct, and then pinch the seam closed. Secure the insulation with short strips of foil tape. Apply a long strip of foil tape along the seam in the insulation.
Fiberglass insulation can touch HVAC ductwork provided the ducts are not leaking or forming too much condensation. The insulation should be snug enough to prevent significant gaps throughout the ductwork.
1" clearance in the rear. The front edge of the microwave (measured at door) should sit at least 3" or more back on the counter or shelf to avoid accidental tipping. If located on the counter near a range, we recommend locating it at least 2 ft away.
A vent damper is an attachment below the vent cover that regulates air flow. This is invaluable to controlling air flow and air balancing, but can sometimes not be a good solution for your particular situation.
You must not vent into the soffits, or even under the soffits unless you are more than a foot and a half below the soffit to allow the wind to dissipate the moisture before it rises back up into the attic.
No, you should never vent your range hood into the attic. The excess buildup of grease and moisture in your attic will ruin it and over time may cause mold damage. Instead, vent your hood through an interior wall or through the ceiling all the way outside of your home.