Choosing the Right Ventilation Equipment
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A good ventilation system involves getting an energy-efficient, quiet fan; designing and installing the ducts properly; and choosing appropriate accessories and controls for your system.
Choose your fan with care. Many inexpensive fans are poorly built. The motor largely determines how well a fan will work, and how much it will cost you over its lifetime.
Fans with shaded-pole motors are the least expensive to buy. But these fans generally don't last long, and they are inefficient; they waste energy and cost a lot to operate. Typical inexpensive bathroom fans use shaded-pole motors.
Fans with permanent split-capacitor motors will cost more, but their motors are about twice as efficient as shaded-pole motors, and should last much longer. These fans are usually rated for continuous operation. As a central ventilation fan, which runs often, this type should cost you much less than a shaded-pole fan over its lifetime.
If your ventilation system is part of an HVAC system, you can make it somewhat better by using a highly efficient fan motor. The most efficient motor on the market now is the variable speed integrated control motor (ICM). It doesn't lose efficiency when it runs at low speeds. This is important in applications such as a double-duty system, where you want to be able to run a fan at low speed for central ventilation and turn it to high speed for heating and air conditioning.
Look at the wattage of the fan you want to buy, and divide this by its capacity in CFM. For higher-capacity spot fans, you want one that uses less than 1 watt per CFM. Low-capacity fans (50 CFM) should use less than 0.4 watts/CFM. If the wattage isn't shown on the label, contact the manufacturer or the Home Ventilating Institute. See Quiet Fans for House Ventilation for examples of quiet, relatively efficient fans.
Bower, John. "Understanding Ventilation: How to Design, Select, and Install Residential Ventilation Systems". Bloomington, IN: The Healthy House Institute, 1995.
Liddament, Martin W. "A Guide to Energy Efficient Ventilation". Coventry, U.K.: The Air Infiltration and Ventilation Center, March 1996.
Lstiburek, Joseph, and John Carmody. "Moisture Control Handbook: Principles and Practices for Residential and Small Commercial Buildings". New York: Van Nostrand Reinhold, 1993.
Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)