To install a ceiling-mounted garage heater, install mounting boards, mount and secure the heater, install the flue and vent, attach the wiring, and connect the gas line. The required supplies are boards, nails, sealant, metal flashing, a block and tackle, clamps, a drill, a jig saw, and basic hand tools.
Screw several sturdy boards across the ceiling joists in one corner of the garage. Attach a block and tackle to an adjacent beam, wrap the cargo straps around the heater, and winch it up to the ceiling. Secure the heater with clamps, and drill bolt holes through the mounting boards. Position the holes according to the bolt holes in the heater frame.
Insert carriage bolts through the holes, and remove the clamps. Screw the flue to the back of the heater, mark the ceiling directly above the flue pipe, and drill a hole there.
Climb up to the garage roof, and cut a circular hole for the flue pipe. Center the opening around the drilled hole. Place the metal flashing over the hole, and trace it. Pick up the flashing, and remove portions of the shingles that fall inside the tracing. Nail the flashing to the roof. Guide the vent pipe down through the flashing, and attach it to the heater flue. Secure a weather ring and pipe cap over the upper end of the vent pipe, and brush sealant over the nails.
Attach the wiring and gas line according to the instructions in the heater installation manual. Seal the gas connections with pipe sealant.