Nance, the microwave might be vented to the outside. Check and see. But I stand by what I said.
Now let me qualify my comments...
Many, many builders use micro over range as standard...it is one appliance that does the work of two and therefore saves them money.
Builders make a good % of their profit in the kitchen, with cheaper "builder" grade cabinets and appliances. How cheap depends on the builder. TV's new home kitchen quality is not great, but actually not too bad for the cost of the homes. I have seen much worse in much more expensive homes.
An exhaust fan vented to the outside is always better than an unvented microwave/exhaust combination, there is no getting around it.
Sorry, P.
