There are three types of microwaves in use today. two are much more common and the third is seldom seen. The original one is the free standing type that can sit on a kitchen counter top. These unit have become very inexpensive and come in a few sizes including especially small units that can be hung underneath a cabinet in order to free up counter top space. The newer style hangs above your range top attached to your wall and upper cabinet and has a combination exhaust fan built in. For the sake of space and convenience it is very common for houses built in the last 15 years to have the over the range microwave / hood combination installed instead of the counter top model. The third type is not widely used. It is part of a combination built in wall oven that has a microwave on top and a wall oven below. These built in wall units come in either a 27″ or 30″ wide models. From a service technician’s stand point, Landers Appliance does not recommend this type of set up. Since the units are married or attached as one piece, we have found that if the microwave or wall oven fails prematurely most people are forced into making the repair because the replacement cost of the combo unit is too prohibitive. If someone has a combination wall oven and it needs to be replaced we usually recommend buying a separate single wall oven and a separate built in microwave to mount above it. Even though this arrangement will cost more to install, since the microwave will require a separate power supply source and an internal platform to support it, in the long run it is much more cost effective. If either the wall oven or the microwave fail and the repair price is too expensive, the replacement costs for the individual appliances are much more reasonable and can become a reasonable option instead of being forced to fix the combo unit.