A variety of mechanical ventilation systems are available to select from, based on local climate and the home’s heating and cooling system. In addition to one of the primary ventilation systems described below, “spot” ventilation fans should also be provided for ventilating kitchens and baths to remove the concentrated moisture and odors that can occur in these rooms. Here is a description of the typical ventilation systems and recommended climates:
- Supply Ventilation Systems – Hot or Mixed Climates: Fresh air is drawn in through an air “intake” vent and distributed to many rooms by a fan and duct system. A fan and set of ducts dedicated solely to ventilation can be used, or an outside air intake can be connected to the main return air duct, allowing the heating and cooling system’s fan and ducts to distribute the fresh air. The benefit of connecting to the return air duct is that outdoor air can be air conditioned or dehumidified before it is introduced into the home. Because supply ventilation systems continually introduce outdoor air, a home can become slightly pressurized. As a result, these ventilation systems are typically not appropriate for cold climates where there is a risk of heated indoor air being pushed through any remaining holes and cracks in the construction assembly where it could reach cold exterior surfaces, condense, and cause moisture problems.
- Exhaust Ventilation Systems – Cold Climates: Indoor air is continuously exhausted to the outdoors with one or more fans often located in bathrooms. Because indoor air is continually drawn out, the home becomes slightly depressurized. As a result, these exhaust ventilation systems are typically not appropriate for hot, humid climates where there is a risk of drawing hot outdoor air into remaining holes and cracks in the construction assembly where it could reach cool interior surfaces, condense, and cause moisture problems.
- Balanced Ventilation Systems – All Climates: With these systems, equal quantities of air are introduced into and out of the home. This is usually achieved using two fans—one to bring fresh air in and another to send indoor air out. The two most common systems are “heat recovery” ventilation (commonly referred to as HRV) and “energy recovery” ventilation (commonly referred to as ERV). HRVs transfer heat from exhaust air to incoming air during the heating season and from incoming air to exhaust air in the air conditioning season to reduce the heating and cooling load and improve comfort. ERVs transfer heat and moisture between the exhaust air and incoming air. This provides additional savings in the summer by reducing the moisture content of the incoming air that would otherwise have to be dehumidified with the cooling equipment or a dehumidifier. ERVs also provide additional comfort in the winter by adding moisture from the outgoing air to the incoming air to help avoid excessively dry indoor conditions.
Source: ENERGY STAR
