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.
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.
Ventilation systems should be installed in all bathrooms. This includes bathrooms with windows, since windows will not be opened during the winter in cold climates.
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 improper terminations locations are:
- 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.
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. Moisture also reduces the effectiveness of thermal insulation.