The first law of thermodynamics, also known as “Law of Conservation of Energy”, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another. The natural transfer of heat flows from a warmer environment to a colder environment. Infiltration through a building entrance door has major impacts on the indoor thermal environment, indoor air quality and energy performance. In our research, we measured differential pressure and air velocity across entrance doors. We also monitored the indoor and outdoor environments in the Environmental Building by collecting data using specialized instruments and sensors. After analyzing the measured data, we were able to calculate the heat transfer of the infiltration through the entrance doors. Finally, we were able to compare the heat transfer rates calculated from local weather and standard weather.