While selecting which exhaust fans to use on greenhouse projects, we calculate which fans have the most appropriate diameters and horsepower motors to move the correct amount of air.  In the process of making these calculations, we make every effort to use only single-speed 115V motors, which last longer and are much more dependable than two-speed 115V motors.  Additionally, we typically ask American Coolair Corporation to outfit our exhaust fans with only 1 horsepower motors, which have longer operating lives than smaller motors.  By pairing a 1 horsepower motor with pulleys designed for a smaller motor, we can make a 1 horsepower motor operate like a smaller motor.  Although a 1 horsepower motor typically costs approximately $5 more than a smaller motor, this small investment will pay large, long-term dividends.  If our Customer is willing to use 230V exhaust fans, this equipment will be more efficient and dependable.  Since 230V small motors and two-speed motors are very dependable, we prefer to use them.