Bathroom Ventilation Ducts and Fans

Inspection

Bathroom ventilation systems are designed to exhaust odors and moist air to the home's exterior. Typical systems consist of a ceiling fan unit connected to a duct that terminates at the roof. The fan may be controlled in one of several ways: Most are controlled by a conventional wall switch.  A timer switch may be mounted on the wall. A wall-mounted humidistat can be pre-set to turn the fan on and off based on different levels of relative humidity The following conditions indicate insufficient bathroom ventilation: moisture stains on walls or ceilings; corrosion of metal; visible mold on walls or ceilings; peeling paint or wallpaper; frost on windows; and high levels of humidity. The most common defect related to bathroom ventilation systems is improper termination of the duct. Vents must terminate at the home exterior. Ducts that leak or terminate in attics can cause problems from condensation. Warm, moist air will condense on cold attic framing, insulation and other materials. This condition has the potential to cause health and/or decay problems from mold, or damage to building materials, such as drywall.  Ventilation ducts must: terminate outdoors. Ducts should never terminate within the building envelope; contain a screen or louvered (angled) slats at its termination to prevent bird, rodent and insect entry; be as short and straight as possible and avoid turns. Longer ducts allow more time for vapor to condense and also force the exhaust fan to work harder; be insulated, especially in cooler climates. Cold ducts encourage condensation; protrude at least several inches from the roof; be equipped with a roof termination cap that protects the duct from the elements; and  be installed according to the manufacturer's recommendations. Above all else, a bathroom ventilation fan should be connected to a duct capable of venting water vapor and odors into the outdoors. Mold growth within the bathroom or attic is a clear indication of improper ventilation that must be corrected in order to avoid structural decay and respiratory health issues.