After much research and speaking with a Kohler factory tech, I settled on a particular generator. According to the factory tech, there are two versions of this generator, one that has minimum site clearance of 60" and one that is certified to 18". I called the this company before ordering to make sure that I would receive the 18" certified version. The salesman insisted that all generators can be sited at 18". This is clearly wrong as the dimension drawings, from their own site, shows a minimum 60" clearance. I have seen other dimension drawing for the "same" unit that has the 18" clearance. The Kohler factory rep stated that only models made after a particular 'specification number' are certified for the closer distance. When I pointed out that the AP salesman was wrong, he hung up on me.