"Understanding Your Home" by Building Inspector Mark Visser
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BATHROOM EXHAUST FAN (with cover removed)
For new installations make sure that the fan capacity is geared to the size of the bathroom. The fan should be located as close as possible to the shower or bathtub.
If the fan becomes too noisy do NOT disconnect the unit but install a new one in it's place.


Open window for spot ventilation
Spot Ventilation - Bathroom Exhaust fan
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Spot ventilation. Bathroom exhaust fan. Insulate vent in attic.

Adequate ventilation is especially important for newer, airtight homes, for older well sealed homes with a high efficiency furnace, and for electric heated homes.
All these homes have one thing in common, having a low rate of air exchange. This means that less warm, moist air is escaping and being replaced with cold air.
Cold air can hold less moisture than warm air and will keep moisture levels low. So, with fewer air exchanges, more moist, warm air will stay in the house, creating more moisture problems. Ventilation can be provided by
Spot ventilation. Spot ventilation can be used selectively to ventilate moisture producing areas such as bathrooms during a shower or the kitchen while cooking. Open windows can also be used for spot ventilation.
Bathroom exhaust fans are required for all bathrooms that have no windows that can be used for venting. Fans should be vented to the exterior.
Vent pipes passing through the attic should be insulated, as illustrated, because the condensation from the warm house air can freeze which may partially or completely block the vent. This frost will eventually thaw and cause water damage to the exhaust fan and surrounding ceiling.

Roughed-in insulated bathroom vents
A blocked vent will also cause problems when not enough air can enter the vent system and can lead to problems flushing toilets and draining tubs and sinks.

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