Rangehood vents which exhaust these contaminants to the outside can be used intermittently as the need arises. Bathrooms are another area where odors and moisture create a need for higher levels of ventilation. All bathrooms, especially those with showers or Jacuzzis, should have a vent fan to exhaust excess moisture outside. Wiring the fan controls to the light switch ensures that the fan will operate when the bathroom is in use, but can cause the fan to be run when not needed. The use of a timer to control the circuit is one way of preventing excessive use.
Laundries are another typical high-moisture area.
All clothes dryers should be vented directly to the outdoors. In all cases, the vents must terminate outside, and not in an attic where moisture can condense and cause damage. All vents should have a backdraft damper to minimize the infiltration of outdoor air when the vent is not being used. In extremely tight houses, it is sometimes necessary to provide some degree of ventilation for the entire home. There are several ways of doing this.