Good afternoon,
What is the minimum clearance from a gas cooktop to the bottom of a microwave above. I believe that it is 24". The one I inspected today is 17". I’m trying to find the code. I’m not sighting the code, I just want to be able to see the wording and better my own education.
Thanks in advance.
Louis,
IRC states the following…
M1503
INSTALLATION OF MICROWAVE OVENS
M1503.1 Installation of microwave oven over a cooking appliance.
The installation of a listed and labeled cooking appliance or microwave oven over a listed and labeled cooking appliance shall conform to the terms of the upper appliance’s listing and label and the manufacturer’s installation instructions. The microwave oven shall conform to UL 923…EXHAUST SYSTEMS
M1901
RANGES AND OVENS
M1901.1 Clearances.
Freestanding or built-in ranges shall have a vertical clearance above the cooking top of not less than 30 inches (762 mm) to unprotected combustible material. Reduced clearances are permitted in accordance with the listing and labeling of the range hoods or appliances.
M1901.2 Cooking appliances.
Household cooking appliances shall be listed and labeled and shall be installed in accordance with the manufacturer’s installation instructions. The installation shall not interfere with combustion air or accessibility for operation and servicing.
Section M1901.1
freestanding or built in ranges shall have a vertical clearance above the cooking top of not less then 30 in to unprotected combustable material, reduced clerance are permitted in accordance with the liating & labeling of the range hood or apoliance.
1901.2 household cooking appliances shall be listed and labeled and shall be installed in accordance wth manf,install instrutions, the installation shall not intetfere with combustion air or access for operation or servicing IRC-06
pg 351
I think 30", but regardless call it out for safety if you feel it is unsafe.
I guess that the only way to truly know the height requirement is to have the manufacturers installation instructions. Would the underside of the microwave be considered combustible. If it is, then the 30 " requirement is needed. It appears that this is up to interpretation.
Most microwaves have trim at the lower portion that is indeed plastic, which makes it combustible.
Richard gave you some good advice saftey issue as it would be considered combustable
Thanks all, I agree and that’s how I’m going to write it up.
All microwave installation instructions say that the minimum distance between the cooktop and the bottom of the **cabinet **that the microwave is to be installed onto, is 30 inches. Typical microwave is around 15 - 17 inches high, so your 17 inches off the cooktop might be alright.
It is much less than 30 " for most combination micro wave range hoods, but it does vary from manufacturer to manufacturer and even from model to model…You would need specs from that unit to be sure…jim
I was going to say , it depends if it is just a microwave or a microwave/rangehood combo. A combo can be installed lower than 30" depending on manufacturers instructions.
“Onto” means “on top of”, not “below”. In any case, the right answer is “in accordance with microwave manufacturer’s printed instructions”, which may be readily available online, knowing the make and model number.
When I used to install them every day for Sears I seem to recall 18"
Just enough for that big old spaghetti pot.
I my memory is not good enough for you try I believe MY home site for SEARS.
You can download lots of trheir material.
Thanks for all the responses. I looked at the installation instructions at Sharp and the clearance is 30" or more to the bottom of the cabinet from the cook top, not the microwave. In theory it seams that 17" is certainly acceptable. It is also 2" clearance from backsplash of stove to bottom of microwave.
Fine, Mr. Preposiiton, the statement that I made is more correct than someone writing it up as a problem if the bottom of the microwave/exhaust unit is less than 30 inches. I agree that you should look up the install instructions and for the most popular units, the top of the microwave needs to be no less than 30 inches from the top of the cook top.
It is 30" from the bottom of the cabinet,(with the cabinet installed a min. 66" from the floor). NOT the bottom of the microwave (exhaust). If the bottom of the microwave was 30" from the top of the stove, that would be a safety hazard and out of reach for some people.
Look at this;
Page four and also other clearances.
http://www.whirlpool.com/assets/pdfs/product/ZINSTALL/9758657.pdf
Marcel 
Couple things to remember, emphasis mine
So,
30 inches clearance above stove.
Can be reduced with hood or microwave.
Installation instructions of hood or microwave take precedence.
Everyone good now? 
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Guess nobody trusts my memory.
Did you post the pics?