Abstract: A mixing/quenching device is in the form of a perforate metal sheet or screen secured at the downstream end of a belled orifice with the perforations defining a plurality of flow paths. The dividing and combining of the flow is passing through the flow paths provides turbulence such that thermal NO.sub.x is reduced.

Abstract: An apparatus for reducing the resonant type noise generated in a combustion driven heating apparatus. A dissipative device is disposed within a hot gas passageway to absorb and attenuate acoustic wave energy and thereby reducing the resonant noise level of the heating apparatus.

Abstract: A belled orifice inlet plate is provided for an induced draft combustion furnace heat exchanger of the type in which an inshot burner produces a hot gaseous combustion that is injected through an opening in the inlet plate into a combustion zone in the heat exchanger. The inlet plate has a flared collar that surrounds the opening at its periphery, and which extends a predetermined distance into the combustion zone. Preferably, the collar should have a depth on the order of one-quarter inch to one-half inch, and the flared portion should have a radius of curvature on the order of about one-quarter inch.