This numerical study investigates the effects of using a diluted fuel (50% natural gas and 50% N-2) in an industrial furnace under several cases of conventional combustion (air with 21% O-2 at 300 and 1273 K) and the highly preheated and diluted air (1273 K with 10% O-2 and 90% N-2) combustion (HPDAC) conditions using an in-house computer program. It was found that by applying a combined diluted fuel and oxidant instead of their an combined and/or undiluted states, the best condition is obtained for the establishment of HPDAC's main unique features. These features are low mean and maximum gas temperature and high radiation/total heat transfer to gas and tubes; as well as more uniformity of theirs distributions which results in decrease in NOx pollutant formation and increase in furnace efficiency or energy saving. Moreover, a variety of chemical flame shape, the process fluid and tubes walls temperatures profiles, the required regenerator efficiency and finally the concentration and velocity patterns have been also qualitatively/quantitatively studied.