by Nick Gromicko, CMI® and Kenton Shepard
- 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.
Newer fans may be very quiet but work just fine. Older fans may be very noisy or very quiet. If an older fan is quiet, it may not be working well. Inspectors can test for adequate fan airflow with a chemical smoke pencil or a powder puff bottle, but such tests exceed InterNACHI’s Standards of Practice.
Bathroom ventilation fans should be inspected for dust buildup that can impede air flow. Particles of moisture-laden animal dander and lint are attracted to the fan because of its static charge. Inspectors should comment on dirty fan covers.
- 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.
- mid-level in the attic. These are easy to spot;
- beneath the insulation. You need to remember to look. The duct may terminate beneath the insulation or there may be no duct installed; and
- under attic vents. The duct must terminate at the home exterior, not just under it.
- temperatures between approximately 45° F and 85° F;
- food. This includes a wider variety of materials found in homes; and
- 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.
- be made from inflexible metal, PVC, or other rigid material. Unlike dryer exhaust vents, they should not droop; and
- have smooth interiors. Ridges will encourage vapor to condense, allowing water to back-flow into the exhaust fan or leak through joints onto vulnerable surfaces.
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. This article is courtesy of InterNACHI and can be found at https://www.nachi.org/bathroom-ventilation-ducts-fans.htm.