Bathroom Fan Terms

CFM: This stands for Cubic Feet per Minute.  It is the minimum airflow needed to achieve eight exchanges of air per every one minute.  To figure out your room's CFM, you will first calculate the bathroom's volume; this is done by multiplying the length, the width, and the height (l x w x h).  Divide this number by 7.5 and you will have your CFM.  All bathroom fans should have their CFM listed on the box.  Choose one with a number equal or higher than your rooms' CFM number.

Foam insulation: This is the preferred type of insulation for a bathroom vent's ductwork.  The insulation is sprayed on using an aerosol spray.  All of the ductwork should be covered with at least one and a half inched of foam insulation.  Insulating your ducts prevents unnecessary condensation build-up which could drip back into the house through the fan.

Grill: This is the metal piece that fits over the inner mechanics of the fan.  Bathroom fans come in a variety of styles, so make sure you find one with a grill that looks right in your room.

Roof vent: This is a vent placed somewhere near the peak of your roof.  At its top, on the outside of your roof, is a roof vent termination cap.  This cap is made especially to prevent outside water vapor (precipitation) from getting into the vent's ductwork.  This type of vent is preferred by some contractors because it eliminates the chance of moisture damage to the roof overhang with a soffit vent.

Soffit vent: This is an outside vent placed where your roof hangs over your exterior wall.  This space-the soffit-is a popular spot for a vent because it is mostly hidden from view and because it is not as expensive to install as a roof vent.

Sone: A Sone is the measurement of sound most commonly used with exhaust fans.  Most likely you will want the quietest fan you can find and afford.  Check the unit's box for its Sone rating.  Four Sones is fairly loud, the average volume of a television set while being viewed.  Three Sones is the volume of your average office, complete with voices and telephones and other machines.  One Sone or lower is hardly audible unless concentrated upon; think of the hum of your refrigerator.

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