I have a client who would like to move thier furnace from the fist floor (house is on a slab) into thier attic. The furnace is a Goodman GMP 100-3. It is currently vented out the top of the unit via b-vent. All of the duct work for the home is in the attic. I am wondering if this unit can be used somehow or changed to a horizontal or downflow and tied into the main trunk in the attic. Suggestions and ideas appreciated.