Smart Fan Controller (SFC) improves indoor air quality and energy efficiency. The SFC automatically adjusts and extends cooling and heating variable fan-off delays based on duration of on and off cycles to improve cooling and heating energy efficiency by 10 to 20% based on Intertek® laboratory tests. The SFC prevents biofilms and maintains proper airflow by removing 0.5 to 0.8 lbs of water per AC cycle to dry evaporator coil after each cooling cycle. According to Montana State University Center for Biofilm Engineering, biofilms are formed by viruses, bacteria, mold, fungi, mites, and dust attaching to water on evaporator coils which can detach from the coil surface and flow into conditioned spaces impacting indoor air quality. https://www.biofilm.montana.edu/