A furnace system for heating a poultry brooder house includes a firebox for burning biomass fuel, and a grate within the firebox for burning the biomass fuel thereon. A distributor assembly may positioned within the firebox and is located directly above the grate. The distributor assembly includes a distributor plate having a plurality of apertures therethrough, and a distributor arm above the distributor plate that is movable relative to the distributor plate to cause biomass fuel supported on the plate to pass through the apertures and fall onto the grate. The furnace system may include a hopper assembly that defines a well for receiving a volume of biomass fuel for delivery to the grate or to the distributor plate.