Ventilation systems are covered under Section R303, Light, Ventilation and Heating, of the Michigan Residential Code. This section of the code requires that habitable rooms have ready access to natural ventilation via doors, windows or other openings to outside air. The minimum size opening is 4 percent of the floor area being ventilated. However, in a cold weather climate like Michigan, it's often more practical to provide some type of mechanical ventilation system.

Because of higher moisture levels, bathrooms must have access to a window opening of not less than 3 square feet, half of which must open to the outdoors. Otherwise, a mechanical ventilation system is required. Both are recommended, however.

Mechanical ventilation is highly suggested for kitchens and bathrooms at the following specifications:

• Kitchen - 150 cfm, 1.5 SONES or less
• Bath - 90 cfm, 1.0 SONES or less

The fan must be properly sized for its intended use or purpose, for the room dimensions and the duct run. Proper installation is critical. Ventilated air must be exhausted directly outside, and not into an attic or soffit area. Insulated ducting is recommended to help prevent condensation of water in the duct. Vent pipes should consist of rigid or semi-rigid pipes laid out to provide the shortest run possible with the fewest elbows. Inside the house, intermittent ventilation systems should be set on a timer separate from any lighting, so a fan can continue to run after the room is vacated.