What Size Should My Bathroom Ventilation Fan Be?

Everyday tasks like showering, bathing and shaving can put home-destructive humidity into the air in your Gresham home. There’s good news still—a modest bathroom ventilation fan can save you from warped wood, mold growth, cracked drywall and other trouble related with a humid bathroom.

Even if you have ventilation fans in your bathrooms, do you know if they’re the right size? Are they as quiet and energy efficient as they could be? Honke Heating & AC is here to answer your questions.

Today’s bathroom ventilation fans are small and modern and they work more quietly and economically than ever before. You’ll find a great range of choices, from simple fans that will get the job done to fans with integrated heat lamps, motion sensors and heat-exchanger ventilation that helps prevent warmed air from getting out through your ventilation. While you have a lot of bells and whistles to choose from, the most critical characteristic of your fan is whether or not it’s big enough to do its job.

Assessed by the cubic feet per minute (CFM) of air they move, a bathroom ventilation fan should be able to replace the air in a bathroom at least eight times an hour. With a standard 8-foot ceiling, your ventilation fan should have a CFM rating at least as high as the number of square feet in your bathroom. Thus, if your bathroom is 5 feet by 8 feet, a CFM rating of 40 would be adequate.

If you have a taller ceiling, the equation gets a little more complex. You’ll want to multiply the width of the room by its height and length, divide it by 60 and multiply by 8. Or, to keep it straightforward, you can heed HGTV’s advice for bathrooms larger than 100 square feet – verify your CFM requirements by increasing 50 CFM for every toilet; 50 CFM for each shower, bath and combo; and 100 CFM for each whirlpool.

If you’re not sure if your bathroom ventilation fan is the proper size, or you know it’s come to the point for a new one, give the pros at Honke Heating & AC at call at 503-663-8033. We’re here to help you make sure you have a ventilation fan that will work hard to guard your home and keep it cozy. 

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