Gravity Heat ManagementGravity Heat Management Gravity Heat Management (Includes 36 Plenum and 10 Flex) Its only natural to want to add a TV above a Rushmore or Boulevard fireplace as it is the focal point of the room. With the addition of the gravity air kit this can now be safely accomplished. The gravity air kit naturally moves the heat being produced by the fireplace through ducting behind the wall to a discharge near the ceiling, reducing the wall temperatures above