Operate Ventilation Systems for Maximum Efficiency

The operating efficiency of a ventilation fan can be reduced 30-50% by the accumulation of dust on fan blades and housing or by shutters that do not operate freely.
Operate Ventilation Systems for Maximum Efficiency - Articles


Regardless of how well a ventilation system has been designed and installed, the system will not function as designed without proper maintenance. When a ventilation system is not operating properly, the results can be unhealthy environmental conditions in the building, pockets of stagnant air, heavy condensation in winter, reduced life and reliability of ventilation equipment, and high repair bills.

The major points to address in any maintenance program for fans and their components are:

  • Clean the fan blades, fan housing, and shutters. The accumulation of just several ounces of dust on fan blades can create enough imbalance to reduce operating efficiency by 30% or more. Clean the fans and components as often as necessary to prevent buildup of dust. In some very dusty environments such as poultry housing, it may be necessary to clean fan blades on a daily basis.
  • Lubricate the fan bearings, motor, and shutters. Any parts that do not move freely should be replaced.
  • Check fan blades for proper rotation. Fan rotation is sometimes reversed when fans are installed if the polarity of wiring circuits is accidentally switched. Since fans move a fraction of their rated capacity of air when running backwards, reversed direction often goes unnoticed in spite of much less efficient performance. Proper direction of fan rotation is generally stamped on the fan housing.
  • Check fan belts for proper tension to prevent slippage. If the belts are cracking, splitting, or fraying, replace now. Otherwise, the belt may fail when no one is available to install a new belt.
  • Inspect the electrical supply cord to each fan. Whenever the insulation begins to crack or split, replace with UL-approved insulated wire.
  • Remove weeds and trim shrubs growing outside buildings close to each exhaust fan. Nothing should obstruct the flow of air from the fan within a distance of two fan blade diameters of the fan. Any weeds or tall shrubs would make it harder for the fan to exhaust the air; hence, the fan would operate with lower efficiency.
  • Remove any obstructions that would limit the flow of air into a fan within a distance of one blade diameter of the fan. Any obstructions to the flow of air would also make the fan operate with reduced efficiency.
  • Check for openings around fan housings that permit air flow to bypass or short-circuit the desired air circulation pattern. Close all other openings in the building such as laps or unions between building sections, service utility entrances, cracks around door frames, and voids in evaporative cooling pads where outside air can enter. Efficiencies of heating, cooling, and ventilation systems can be drastically reduced by the presence of such openings.
  • When necessary to replace a fan assembly, always replace with a fan rated according to AMCA (Air Movement and Control Association) standards. Such fans will carry an AMCA seal on the fan housing and in the sales literature.
  • Replace any fan motors with explosion-proof, totally-enclosed motors with sealed bearings for those motors operating in dusty or humid environments, such as a poultry house or greenhouse. This type motor is required to protect the motor windings from the corrosive effects of high humidity and dust accumulations that would otherwise shorten the service life of the motor.
  • Calibrate thermostats and humidistats to ensure that fans operate according to the desired environmental conditions. Be sure to carefully wipe any accumulated dust from the sensing elements of the controls before calibrating. The sensing elements should be placed at or near the level of the plants or animals - rather than human level - to ensure the most accurate environmental control for the plants or animals.