Recent developments in heat recovery systems allow for preheating of combustion air up to temperatures of 1300 degrees C and, thus, fuel savings up to 60% are achievable. In conventional burner/furnace designs, the higher the combustion air temperature the higher the NOx emissions. However, the most recent developments allow for low NOx combustion using high temperature combustion air. The objective of this paper is to establish conditions under which industrial furnaces should be operated in order to maximize the efficiency and minimize the pollutant emissions including carbon dioxide. To this end, semi-industrial scale experiments have been carried out using natural gas and vitiated air at 1300 degrees C. A Nippon Furnace Kogyo burner that features a central air jet and two fuel gas injectors was used. Comprehensive in-furnace measurements of velocities, temperature, gas composition (O-2, CO2, CO, H-2, NO, CH4) and radiation have been carried out. The furnace was operated under conditions resembling a well-stirred reactor; the temperature and chemistry fields were uniform all over the furnace. Almost the whole furnace volume was filled with combustion products containing 2-3% oxygen at temperatures in the range 1350-1450 degrees C, despite the high temperature (1300 degrees C) of the vitiated air. The natural gas jets entrained many of the combustion products before they mixed with combustion air. This mode of combustion resulted in high and uniform heat fluxes and low NOx and CO emissions. It was concluded that industrial furnaces of tomorrow are likely to be designed as well-stirred reactors equipped with high efficiency heat regenerators. Conventional burners will be either replaced with individual fuel and air injectors or substantially redesigned to facilitate uniformity of combustion conditions within the furnace.