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Ventilation Needs for Bathrooms

Most residential building codes for new homes now mandate adequate bathroom ventilation by a powered exhaust fan. However, if your house was built before 2003, a bathroom window that could be opened by hand may have been the only venting requirement. There are good reasons behind changes in the code.

Why Is Ventilation Important?

Bathrooms are ground zero for growth of toxic mold and mildew. The combination of high levels of water vapor in the air due to bathing and showering with warm temperatures concentrated within a relatively small, enclosed room make the typical bathroom a perfect environment for fungal growth and bacteria. Repeatedly exposed to steam produced by hot water, drywall also deteriorates, doors and drawers warp and paint and wallpaper peel. Over the long term, water vapor permeating the ceiling and walls can cause wooden structural components to decompose, too.

How Much Ventilation Is Enough?

The general formula is one cubic foot per minute (CFM) of exhaust fan ventilation per square foot of bathroom floor. The minimum amount is 50 CFM for bathrooms of 50 square feet or less. For a 10’ x 10’ bathroom (100 square feet), for example, the fan should be rated for 100 CFM.

A powered bathroom fan must connect to a vent duct that extends to the exterior of the house and exhausts into outdoor air. Fans must not exhaust into interior spaces such as the attic or the crawl space where discharged moisture will trigger mold contamination and damage structural components.

Fans should be controllable by a switch or by some automatic method. Ideally, a bathroom fan should run at least 15 to 20 minutes following showering or bathing to fully exhaust moist air and steam. Since occupants of the bathroom have usually left the room by then, a timer switch that keeps the fan running for a specific duration after activation, then shuts the fan off automatically, is preferable to a simple manual on/off switch.

For more about the importance of adequate bathroom ventilation, in Orlando contact Rinaldi’s Energy Solutions.

Our goal is to help educate our customers in Orlando, Florida and surrounding areas about energy and home comfort issues (specific to HVAC systems).