Current trend in HVAC industry is to use increased air flowrate to increase the air conditioners efficiency compared to when testing standards were originally developed. Also, the current standard (ASHRAE 37) has limited guideline about inlet ductwork design while testing an air handling unit. It doesn’t mandate using one but just recommends using one if the space permits. As there is no specific length (only the minimum length) for the inlet ductwork is provided in the standard, testing of the air handlers at different inlet duct length could lead to false performance of the fan. The purpose of this study is to develop an inlet duct design guideline with reduced length for inclusion in the AHRI and ASHRAE testing standards that reduces the risk of false testing failures and will lead higher integrity of the testing results at different laboratories. This study will evaluate the performance of fan in an indoor air handling unit for a number of parameters such as flow rate, inlet duct length, unit capacity, fan type and motor configuration. An additional objective of this project is to reduce the overall height of the testing setup (inlet duct+ test unit+ outlet duct) by reducing this inlet duct length while maintaining the equivalent fan performance as of the standard case (minimum inlet duct length as per ASHRAE 37).