Choosing Ventilating Fans for Your Portland Metro Home
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Choosing Ventilating Fans for Your Portland Metro Home


Removing stale air or whisking out offensive odors is the primary function of fans in your home. However, many homeowners don’t realize there’s a bit of science behind choosing ventilating fans based on the size of the area to ventilate and the length of the vent the air has to pass through. 

The Home Ventilating Institute (HVI) recommends that kitchens have 15 air changes per hour (ACH) and bathrooms have 8. The fans are sized by the cubic feet per minute (CFM) that they remove from a space. Kitchen and bathroom fans require different formulas for calculating the size.

Bathroom fans

Multiply the length, the width and the height of the bathroom to get its cubic footage. Then multiply the result by 8, which is the standard for bathroom ventilation. If the bathroom measures 8 feet long, 6 feet wide and the ceiling plate is 8 feet, the cubic footage is 384. Since the air needs to be changed 8 times per hour, the total would be 3,072. Dividing that by 60 minutes per hour yields 51, so choosing ventilating fans of 51 would be adequate.

If the bathroom’s dimensions are larger than 100 square feet, you’ll have to calculate it by the number of fixtures in the bathroom. The toilet, tub and shower require 50 CFM, while a whirlpool tub requires a fan rated at 100 CFM.


The ventilating fan for the kitchen is based on the BTUs, or British thermal units, of your stove. Each 10,000 BTUs requires a fan that can remove 100 CFM. Your owner’s manual for the stove will indicate its BTU measurement.

Besides the kitchen and bathroom areas, ventilating fans are useful in homes that have attached garages and attics that get exceptionally hot in the summer. If you store a lot of chemicals in the garage, the by-products can easily enter your home through the attached wall and door. Fans in the attic pull cooler air inside the attic, keeping your home cooler.

To learn more about choosing ventilating fans, contact Roth Heating & Cooling. We’ve been providing HVAC services for greater Portland since 1976.

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