Ventilation is the process of mechanically exhausting stale indoor air to outside.   It is an important contributor to the health and comfort of an indoor environment as it provides oxygen for the occupants and removes internal contaminates.  The appliances that are used to ventilate homes include intermittent fans like bathroom exhaust fans and kitchen range fans along with continuous ventilation provided by a Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV).   Continuous ventilation appliances are also known as Air Exchanges play an important role is managing moisture generate by people, plants, pets, cooking, showering and laundry.  Equally as important, air exchangers manage contaminates from off-gassing of interior finishes and furnishings.  Many municipalities require not only ventilation specifications but also design and layouts for the purpose of permit applications and contractor installation.