Single fan kit has a 4.7 inch [120mm] diameter fan with 73cfm airflow rating and 33dB noise rating. Housing measures 4.7 in. [120mm] square x 1.5 in. [38mm] deep and has a black finish. An integral (variable speed) thermostat probe automatically activates the fan when ambient temperature reaches 80°F (26.6°C), increasing and decreasing speed as it adjusts to the ambient temperature. This power-saving feature ensures efficient operation while saving wear and tear on the fan.