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Bathroom Exhaust Fans

It is critical that your bathroom has ventilation and installing an exhaust fan is the best cure-all. Every time you use your bath or shower, it creates high levels of humidity that create a breeding ground formold and mildew. Add to that the issue of long-term exposure of moisture and humidity to your bathroom walls. Without proper ventilation, the excess moisture can crack and peel paint, warp doors, rust fixtures, and eventually cause the deterioration of joists and framing above the bathroom. This is a perfect example of the well intended adage “an ounce of prevention is worth a pound of cure.”

How it works

An exhaust fan is a ventilation device installed into the ceiling or high up on the wall and is ducted to the exterior of the house. It pulls out (or vacuums up) all the steamy humid air, thus improving the quality of the indoor air.

Why you need one

Because exhaust fans suck up excess moisture, odors, and other pollutants, it creates a healthier environment for you and your family. It also protects your walls, ceiling, floors, cabinets, and fixtures, saving you from costly repairs. Another benefit not to be overlooked is that when you step out of the shower or bathtub, your environment is dry and your mirrors aren’t all steamed up. There’s nothing worse than taking a shower in the summer and feeling like you can never really dry off because your bathroom has turned into a steam room.

Shopping and what to look for

Look for exhaust fans with the HVI Certified label (Home Ventilating Institute.) This is the industry’s “seal of approval” and basically tells you that the unit has gone through rigorous independent performance testing and met the industry standards. There are a wide range of exhaust fans available that offer different capacities to accommodate the air exchange requirements. If you’re a do-it-yourselfer – great; if not, you’ll want to contact an HVAC contractor (see our provided list of quality licensed contractors) to help you choose the right product for your bathroom and to do the installation for you.

Guidelines for ventilating both large and small bathrooms

Air movement capacity is measured in cubic feet per minute (CFM) and is an essential consideration during the initial planning stage. You’ll want to be sure to have adequate CFM for the square footage of your bathroom.

Large bathrooms

For bathrooms measuring over 100 square feet, the recommended ventilation rates are based on the number and type of fixtures present. Example, the bathroom is 20’x12’ and there is a tub (non jetted), a shower enclosure, and an enclosed toilet: toilet = 50 CFM, shower = 50 CFM, bathtub = 50 CFM, and tub = 50 CFM, your total CFM would be 150. Jetted tubs = 100 CFM.

Small bathrooms

For bathrooms up to 100 square feet, it is recommended that an exhaust fan provide one CFM per sq. foot (approximately eight air changes per hour) to properly ventilate the room. Example, the bathroom is 8’x 5’ with 8’ ceilings. Multiply 8 x 5 = 40 feet. You would need a 40 CFM.

Duration of ventilation

It is recommended that the fan be left on for 20 to 30 minutes after use. For steam showers, it is recommended that a separate fan be installed in the room that can be turned on after use.

Performance, features, options

Depending on your budget and style preference there are some bells and whistles you have the option of including: light, heating element, or a timer or humidistat for automatic operation.

Some people like the built-in privacy feature of a louder fan while others prefer quiet solace. Either way, you’re in luck – you get to pick the noise level of your exhaust fan. The sound levels are measured in sones. 4.0 sones is equivalent to the sond of television operation. 3.0 sones is equivalent to humming office noise. 1.0 sones can be likened to your refrigerator. 0.5 sones is on the same scale as softly rustling leaves. So, with 4.0 being the loudest and 0.5 being the quietest, you now have an idea of what sone level you might prefer.

Other considerations

  • If your bathroom ceiling is taller than eight feet, you may require additional ventilation.
  • If you have a separate enclosed stall area for your toilet, it should have its own exhaust fan.
  • Don’t forget your replacement air, a.k.a. makeup air. Keep at least a ¾” clearance from your bathroom doors to the floor to allow for fresh air to flow into the bathroom.
  • To ensure building code requirements, as well as ventilation expectations, only choose an HVI certified product. Inflated performance ratings are common for bathroom exhaust fans that are not HVI certified.

All in all, the relatively small investment in an exhaust fan is worth all the benefits of living healthier, being more comfortable, and ensuring your homes protection against rot, mildew, and mold.



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