a. Mechanical: Mechanical ventilation systems circulate fresh air using ducts and          fans, rather than relying on airflow through small holes or cracks in a home’s walls,        roof, or windows. Better indoor air quality, control over intake and exhaust,                    improved comfort level are some of the advantages of Mechanical Ventilation.

      b. Natural: Natural ventilation relies on the wind to naturally ventilate the home by        entering and leaving windows, depending on their orientation to the wind. In                coastal climates, many seaside buildings are designed with large ocean-facing              windows to take advantage of cooling sea breezes. For drier climates, natural                ventilation involves avoiding heat buildup during the day and ventilating at night.

      c. Combined: Combined ventilation relies on the natural driving forces to provide           the desired flow rate. It uses mechanical ventilation when the natural ventilation           flow rate is too low. The size and number of exhaust fans depends on the                       targeted ventilation rate, and must be measured and tested before use.

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