Venting Microwave Distance from Stove Cooktop

[Pauls_HVAC_Woes]

Hi all, brand new here so therefore this is my first question that I would greatly appreciate help with.  Does anybody have a clue what the distance from a gas stove cook top to the bottom of a microwave. All I can find is 30" to the bottom of the cabinet above the microwave? I've checked the code book, the manufacturers instructions for both the stove and the microwave etc. Today we removed the microwave above a stove as it was only just 15" above the top of the new stove, now I am having my doubts though. I am aware that by code it needs to be vented, but when do you draw the line if there is no indication anywhere. Thanks to all that take the time to help it's greatly appreciated.

[Porcupinepuffer]

I'm pretty sure there isn't a standard clearance to the bottom as it wouldn't be considered combustible. The 30" to the cabinet is one that has be followed. Along with depth and height of the nearby cabinets that are usually on both sides coming down close to the stove. If the manual for the stove or microwave doesn't have anything more stringent and you meet the 30", then it should be fine even if it's only 15" from the stove. There may also be minimum requirement of CFM of exhaust that the gas range might call for that the microwave exhaust may not meet. These combo microwave/exhaust hoods don't typically move nearly as much CFM as a good quality range hoods do.