This article addresses effect of input air upon combustion performance and environmental pollution of biodiesel and diesel in a semi industrial boiler. The thermal capacity and exhaust temperature as the combustion performance and emissions like CO2, SO2, CO, and NOx are investigated and plotted over a wide input air to the boiler at a constant fuel pressure of 160 psi and diffuser setting at 3 mm. Indeed, this article demonstrates, in a non-premixed combustion of biodiesel and diesel, how performance of a boiler changes with increasing and decreasing of input air to the boiler. Afterwards, the trend of emissions with change in the input air will be depicted as well.