Totally false. One year parts and labor warranty is standard.
More importantly, with such small clearance, you need to worry about airflow as the factory specifies 2-3 inches clearance around the perimeter.
Otherwise some provision to direct airflow through the unit, cool in the bottom, warm exhausted from the top. Generally, about 850 CFM external airflow needed if installed in an enclosure.
Techniwizard posts as an Independent Servicer