Patent ID: 8025049

Claim:
A high efficiency furnace comprising: a furnace enclosure having an interior volume and a distribution air outlet opening on the enclosure that is adapted for communication with an air distribution system; a primary heat exchanger in the furnace enclosure interior volume, the primary heat exchanger being adjacent the distribution air outlet opening; a secondary heat exchanger in the furnace enclosure interior volume, the secondary heat exchanger being adjacent the primary heat exchanger and being separate from the primary heat exchanger; a fan wheel in the furnace enclosure interior volume, the fan wheel having an outer diameter dimension, an axis of rotation that defines mutually perpendicular axial and radial directions, and the fan wheel being rotatable in a rotation direction around the axis of rotation; a blower housing in the furnace enclosure interior volume, the blower housing having an interior volume containing the fan wheel and an air flow outlet opening positioned adjacent the secondary heat exchanger to direct a flow of air from the blower housing interior volume through the air flow outlet opening, then through the secondary heat exchanger, then through the primary heat exchanger, then through the furnace enclosure distribution air outlet opening, the blower housing having first and second side walls on axially opposite ends of the fan wheel and on opposite sides of the air flow outlet opening, and the blower housing having an outer wall between the first and second side walls, the outer wall having a volute portion that spirals away from the fan wheel axis of rotation as it extends from a first end of the volute portion at one side of the air flow outlet opening around the blower housing interior volume to a second end of the volute portion at an opposite side of the air flow outlet opening from the first end, and the blower housing outer wall having a radial dimension from the fan wheel axis of rotation to the second end of the outer wall that is at least 0.91 times the fan wheel outer diameter dimension, and the blower housing air outlet opening having a minimal radial dimension that is at least 0.73 times the fan wheel outer diameter dimension.