A burner is disclosed having a burner chamber with heavily insulated heat retaining walls and a series of off-center mixers located at one end thereof. A uniform concentration gas/air mixture to 50% additional fuel above the lean flammability limit coming from the mixer tubes is ignited in the burner chamber due to the recirculation of combusting gas and air back to the end of the burner chamber above auto the ignition temperature for the mixture. The particular mixture disclosed utilizes 0.55-0.7 equivalence ratio. With the present burner, oxidant and fuel are respectively supplied to each mixer by respective common oxidant and fuel plenums. In this way, fuel and oxidant are mixed near the point of combustion, enhancing safety and permitting the construction of larger burners.