My home contains a non-metal, fiber board duct system, is that a problem?

No, however, installation on fiber board duct will require additional means of support to carry the full weight of the unit when it is full of water. This could include a floor stand or a hanging bracket from the ceiling. It is also recommended that the mounting plate screws should also be re-enforced on the front of the duct with a small metal plate, or oversized washers.