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These days all the over- the-range microwave ovens are approximately the same size. So, you will be able to select just about any manufacturer and replace it.
They generally hang down approxiamtely 16 1/2" and come off the back wall 15 1/2".
They are approximately 29 7/8" wide and fit into a 30" wide opening.
Your model should be about those dimensions also.
Please let me know if you would like more information and/or clarification.
This is a reference to the interior cavity. So, if you want a larger inside you may wish to consider this point. They can be as large as 2.0 or so. Most people don't find that they need the extra space. However, everyone is different.
Larger units do have more power and that means you can heat foods just little bit quicker.
Almost all units can be used either ducting to the outside or reciruclating inside. So, again you will have a large selection to chose from.
You probably will need to recirculate the exhaust inside. GE brand will require you to purchase a charcoal filter (in addition to the unit) for this so that the smoke and smell will be taken out before it goes back into the kitchen. GE's charcoal filter is approximately $40.00.
Whirlpool's and Frigidaire's over-the-range microwave ovens usually come with the charcoal filter.
They all have lights and grease filters.