The method for heating the furnace chamber produces high momentum levels during the heat treating cycle so as to obtain substantially uniform temperature throughout the charge. The method includes initially firing a plurality of high velocity burners at substantially maximum fuel input and in substantially stoichiometric ratio. Thereafter, the fuel input is reduced while maintaining the stoichiometric ratio at least during the high input portion of the cycle. Excess air is introduced external of the combustion zones of the burners on a predetermined signal such as a given fuel input reduction to maintain the desired momentum level within the furnace. The apparatus comprises a high velocity burner having associated therewith an excess air unit for discharging excess air external of the combustion chamber or port block of the burner. The excess air unit can be integral with the burner so as to supply excess air through the burner port block or a separate unit can be provided which is connectable to the burner and about the port block which defines the combustion chamber.