Over the range microwaves usually have a fan underneath them that can pull air up and away from the range. Once connected to ducting that vent to the outside, these fans can help clear a kitchen of smoke or potent odors. If there is a leak in this ducting, the odors and smoke seep out and back into the house. The following steps explain how to look for leaks in the ducting and reseal them.
Step 1 - Identify the Areas That Need to Be Resealed
The areas that are usually in need of resealing are joints where two pieces of the ducting merge. Examine any joints in the ducting, as well as, the area where the ducting meets the hood portion of the microwave, looking carefully for leaks. When the fan is running, if there are leaks in the pipe, one may be able to feel a small draft from these areas. If there does not seem to be any leaks along the joints, the lengths of ductwork themselves must be inspected for holes.
Step 2 - If a Leak is Found Around a Joint
If a leak is found along a joint, use a brush to liberally apply a mastic over the entire joint. Mastic is a glue-like substance that, when dry, will form a rubbery seal over the area. Metal-reinforced tapes that are rated for higher temperatures may also be wrapped around the ducting instead of the mastic; however, despite its name, duct tape is a poor material for sealing ducting and should not be used.
Step 3 - If a Hole is Found in the Ductwork Piping and Not at a Joint
Holes are generally patched with a small piece of sheet metal. Apply the sheet metal to the duct with an epoxy that is rated for bonding metal to metal. Once dry, cover the patch with mastic to ensure it is sealed.
Step 4 - To Reseal the Space Between the Wall and the Ducting
If looking for the leaks has created a space in the area around the ducting where the piping passes through the wall, simply fill the gap with either an expanding spray foam or caulking.