Filters are used in HVAC systems for both commercial and residential buildings to protect the equipment and improve indoor air quality in conditioned spaces. Although there are many benefits of using the air filter in an air conditioning system, the resistance associated with it can increase fan energy use and may adversely affect air condition system performance and efficiency. The paper explores the impact of air filtration on energy consumption for a typical air conditioning (AC) system with constant or variable-speed fan. A whole building simulation model is used to simulate the annual energy consumption for various air condition system capacities, different levels of filter cleanliness, and various filter minimum efficiency reporting value (MERV). The results indicates that with a constant-speed fan, the cooling energy use increases as the filter gets dirty over time and the energy use in the fan may increase but this depends heavily on the investigated fan performance curve. With a variable-speed fan, the fan energy uses increases with dirty filter but the cooling and heating energy uses are slight affected. The fan energy use rise due to the dirty filter depend mainly on air system capacities, filter MERV ratings, and the degree of the filter cleanliness.