| Ventilation |
 Vapor Barrier |
A bathroom exhaust fan helps remove both moisture and odors. It is crucial to exhaust moisture to prevent it from entering building cavities and damaging framing, or even deteriorating a house's exterior walls.
In tight houses, vent fans, clothes dryers, and kitchen exhaust fans can create a negative pressure, so that they draw air into the house through holes in the framing, chimneys, and even exhaust flues. This can cause backdrafting in combustion appliances, a serious health hazard. While the bathroom can be maintained at a negative pressure to control odor problems, it is best if the rest of the house is kept at a slightly positive pressure. In hot, humid climates, it is best to operate the exhaust fan only when the bathroom is in use, so that the negative pressure does not draw humid outside air into the building cavities.
 Vapor barrier |
Heat Recovery Ventilators (HRVs) , also known as air-to-air heat exchangers, exhaust contaminated indoor air and replace it with outdoor air, improving the air quality in the home. They reclaim heat (some units also reclaim humidity) and transfer it to incoming fresh air, either maintaining neutral pressure in the house or creating a positive pressure inside relative to outside. The HRV can be ducted to the bathroom fan and kitchen exhaust, so that every time the fans come on, the HRV is engaged to capture heat from the exfiltration. In drier climates where indoor moisture is beneficial, enthalpic wheel HRVs capture some of the humidity as well.
