A sub-base is installed under the sleeve of a PTAC unit. It is often used to stabilize the unit, giving it a support with leveling legs. A non-electrical sub-base simply stabilizes your PTAC unit without any connections.
The sub-base may be installed onto wall sleeve either before or after sleeve installation. Minimum clearance between wall sleeve bottom and finished floor is 3¾"; maximum height clearance from bottom of wall sleeve and finished floor is 5". Minimum clearance between wall sleeve flange and finished wall is 2¾".