A burner , comprising: a fuel nozzle assembly configured to output a gaseous mixture including fuel and oxidant; and a porous flame holder defining gas passages extending between an upstream surface and a downstream surface of the porous flame holder , each having a minimum lateral dimension (DL) equal to or greater than a fuel quenching distance, aligned to receive the gaseous mixture , the gas passages being configured to pass a combustion reaction supported by the gaseous mixture; wherein the gas passages include a wall configured to receive heat from a reacting portion of the gaseous mixture , radiate the heat toward an unreacted portion of the gaseous mixture , and receive the radiated heat adjacent to the unreacted portion of the gaseous mixture ; characterized in that the fuel nozzle assembly includes a plurality of nozzles configured to output the gaseous mixture , the burner further comprises an air source configured to output substantially pure air, a lower story tile , and the porous flame holder supported above the lower story tile by a support structure ; a start-up flame holder configured to hold the combustion reaction having a richer fuel mixture than the porous flame holder , wherein the start-up flame holder is configured to support the combustion reaction at a location configured to pre-heat the porous flame holder , wherein the fuel nozzle assembly is configured to mix the gaseous mixture sufficiently to substantially destroy Taylor layers between pure fuel and air carrying the oxidant and that the gas passages are configured to hold the combustion reaction between the upstream surface and the downstream surface , whereby the production of NO x is decreased. a fuel nozzle assembly configured to output a gaseous mixture including fuel and oxidant; and a porous flame holder defining gas passages extending between an upstream surface and a downstream surface of the porous flame holder , each having a minimum lateral dimension (DL) equal to or greater than a fuel quenching distance, aligned to receive the gaseous mixture , the gas passages being configured to pass a combustion reaction supported by the gaseous mixture; wherein the gas passages include a wall configured to receive heat from a reacting portion of the gaseous mixture , radiate the heat toward an unreacted portion of the gaseous mixture , and receive the radiated heat adjacent to the unreacted portion of the gaseous mixture ; characterized in that the fuel nozzle assembly includes a plurality of nozzles configured to output the gaseous mixture , the burner further comprises an air source configured to output substantially pure air, a lower story tile , and the porous flame holder supported above the lower story tile by a support structure ; a start-up flame holder configured to hold the combustion reaction having a richer fuel mixture than the porous flame holder , wherein the start-up flame holder is configured to support the combustion reaction at a location configured to pre-heat the porous flame holder , wherein the fuel nozzle assembly is configured to mix the gaseous mixture sufficiently to substantially destroy Taylor layers between pure fuel and air carrying the oxidant and that the gas passages are configured to hold the combustion reaction between the upstream surface and the downstream surface , whereby the production of NO x is decreased. <EOS>