A wall sleeve is required for all new PTAC unit installations. A sleeve helps bear the weight, protects and helps insulate your PTAC system. Your 42" PTAC unit fits right into the sleeve, which is mounted through the wall. A typical wall sleeve is 13 3/4" deep.
This kit allows you to add an additional 2" to the depth for installation in slightly thicker walls.It attaches with screws to the standard wall sleeve.