Abstract: A control system to control the operation of a furnace (10) having a fuel control unit (26) to supply fuel to a burner (24) includes a limit switch (48) within furnace (10) to detect an overheated condition. The limit switch (48) opens when a reference temperature is reached, shutting down the furnace (10). A logic unit (40) senses the state of the limit switch (48) and measures the shutdown period, and notes whether the shutdown period exceeds a predetermined interval. The logic unit (40) opens a lockout switch (38') that controls the fuel control unit (26) if the furnace is subject to a number of consecutive prolonged shutdowns that exceeds a predetermined limit.

Abstract: An abatement member for inhibiting formation of oxides of nitrogen in a gas-fired furnace by controlling peak flame temperatures and residence times at the peak flame temperatures is described. The combustion system has at least one heat exchanger conduit having a flow path therethrough and at least one gas burner for burning fuel to produce a combustion flame. The abatement member has a porous refractory body portion having at least one section which is disposed transversely to the direction of flow of gases through the conduit. In one embodiment, the abatement member is a metallic screen having a serpentine shape and positioned within the fire tube. The combustion flame is directed toward and into the inlet of a fire tube and through the screen whereby the screen absorbs thermal energy from the combustion flame at a rate which limits peak flame temperatures to levels which inhibit formation of oxides of nitrogen.