Only a licensed contractor should perform the installation of a direct vent furnace. He should be trained to handle the plumbing, gas, electrical and venting aspects of a direct vent furnace and be aware of all local and national codes.
The direct vent furnace comes as a ready-assembled unit. The unit consists of two main components: the outer housing and the flue system. First find a location to install the furnace. It needs to be on an outer wall for proper venting of the flue gases. Check for the clearances needed from the furnace and vent.
Ensure the gas piping and electrical wiring connection availability to the furnace. Drill the vent openings for the electrical wiring and the gas piping. Install the pacer plate and then mount the furnace. Install the cabinet housing over the furnace. Do the thermostat installation.
The outer housing houses two of the main operational components. One is the firebox. The sealed firebox only allows the combustion gases to leave the system and exit the building. The space between the firebox and the outer housing is the second operational component. This section is used to add hot air to the room, and not the exhaust gases.
The flue system consists of the inner flue and the outer flue. The external flue draws air into the bottom of the sealed firebox for combustion. The internal flue takes the hot exhaust directly to the outside either through the roof or the adjacent wall.