Premix furnace burner

A premix furnace burner for a gas combusting furnace. The furnace burner includes a premix chamber and a burner plate assembly. The burner plate assembly is comprised of a burner plate with a plurality of relatively small apertures for the passage of a mixture of combustible gas and air and an annular ring for retaining the burner plate. The annular retaining ring determines the capacity of the furnace burner by appropriately sizing of the opening in the annulus of the retaining ring to sealingly overlay a selected portion of the burner plate apertures. The retaining ring further secures the burner plate in the correct operational position while simultaneously permitting the burner plate to expand and contract in response to temperature changes induced by combustion of the gas and air mixture. The premix chamber includes therein a blower impeller driven by a two-speed motor and a control means for selectively operating the impeller at a relatively higher or lower speed to vary the rate of flow of the mixture of combustible gas and air and thereby vary the firing rate of the furnace.