Heat recovery ventilation (HRV) systems or air exchangers allow a home to maintain high indoor air quality without excessive additional energy costs.  HRV systems consist of two separate air-handling systems; one collects and exhausts stale indoor air; the other draws in outdoor air and distributes it throughout the home.  As the exhaust and outdoor air streams pass through the HRV,  heat from the exhaust air is used to pre-heat the outdoor air stream. Only the heat is transferred; the two air streams remain physically separate.  This dramatically reduces the energy needed to heat outdoor air to a comfortable temperature. HRV provides fresh air and improved climate control while also saving energy by reducing heating and cooling requirements for many applications.