As the name suggests, the term convertible means that a microwave or convection microwave oven can be converted from venting to non-venting ducting modes, if required. Doing so means finding the appropriate recirculation kit part number, placing an order with an authorized parts distributor, and conducting a little DIY.
As for why you may wish to switch to the recirculating venting option, it’s something that may be necessary if looking to reposition your microwave. What’s important to remember is that virtually all building codes state that external venting is mandatory for an over-the-range microwave. It is a formal legal requirement to have the appropriate ventilation system installed in order to deal with the fumes produced by an over-the-range microwave oven.
A recirculating venting system wherein the microwave vents internally is therefore not an option with these types of appliances.
Nevertheless, those who own range microwaves may decide at a later date to reposition the microwave oven. They may choose to move it away from the kitchen stove and place it somewhere on a countertop – away from the stovetop surface.
At which point, it no longer needs to be hooked up to an external venting system or duct. A recirculating kit can be used with a convertible microwave to channel the emissions safely back into the kitchen.
Something that could prove significantly cheaper than purchasing a new microwave oven outright. Particularly if you bought the best microwave, you could afford it in the first place, which in the case of external venting microwaves can be quite expensive.