The proper distance between a microwave oven and a range top will vary based on what kind of microwave you're planning to use. If you want to install an over-the-range microwave, you will need much less space between the stove and microwave than you would for a countertop microwave as these models are designed to withstand higher external temperatures.
If you plan to use a countertop microwave near a cooktop, the microwave should be far enough away from the range to avoid any danger of fire or heat damage to the microwave and also to keep the microwave away from any spatter from food cooking on the range. In general, countertop microwaves should be at least 2 feet away from the cooktop, and because these models are not designed for over-the-range use, they should never be mounted above a cooktop.
Over-the-range microwaves include built-in ventilation systems for filtering and venting exhaust from the cooktop. These models offer the option of venting either through a duct to the outside of the home or directly back into the kitchen. The recommended clearance between these units and the stove varies based on who you ask.
The International Residential Code, the building code on which most local building codes are based, requires a clearance of 30 inches between the top of a range and any combustible surface, but it specifies that over-the-range microwaves, which are designed to tolerate less clearance, should be mounted according to their manufacturer's instructions.
The National Kitchen and Bath Association recommends that the bottom of the microwave should be no higher than 54 inches above the floor, which would allow for 18 inches of clearance between the microwave and the typical cooktop height of 36 inches.
Some manufacturers allow smaller clearances. General Electric, for example, requires that its microwaves be mounted with a minimum of 66 inches between the floor and the top of the microwave, which results in a clearance of between 13 and 16 inches from the microwave to the cooktop. Tight clearances, however, may make it difficult to use large pots on the cooktop.
Range Output Limits
Manufacturers also place limits on the output capacity of cooktops suitable for use in conjunction with over-the-range microwaves. GE specifies, for example, that its over-the-range microwave models not be installed over any range whose burners output more than a combined 60,000 British thermal units, which is drastically higher than the average 7,000 BTUs of a standard home range. So unless you have a lot of very powerful burners, this is one limit you probably don't need to worry about.
Microwave Landing Areas
The National Kitchen and Bath Association recommends that there be a clear landing area near a microwave so that cooks have a place to easily set down food taken from the microwave. The landing area should be at least 15 inches wide and be located above, below or adjacent to the handle side of the microwave's door. In the case of an over-the-range microwave, there is obviously not space for a landing area immediately below the microwave, so maintaining a clear counter space next to the cooktop is important.