Supply ventilation works in just the opposite way as exhaust ventilation. Outside air enters the house through a dedicated supply fan or through the central HVAC system air handler and escapes through leaks in the building envelope.
With the supply ventilation approach, the outdoor air inlet should be placed to avoid known areas of contaminants, such as the garage, barbeque areas, and chimneys. If a dedicated fan is used, care must be taken to avoid introducing too much outdoor air into one location and creating uncomfortable conditions. The air handler or supply fans can be located on the exterior of the house or dwelling unit, or in the garage, attic, basement, or mechanical room.
The ventilation air can be distributed by a dedicated ventilation air duct system that is separate from the central forced air distribution duct system. Alternatively, the central forced air heating/cooling system air handler can be configured to function as a supply ventilation system by installing a dedicated ventilation air duct that connects to the air handler's return plenum at one end, and connects on the other end to the outside of the dwelling to access fresh air from outdoors. This strategy, called Central Fan Integrated (CFI) ventilation, uses the negative pressure in the return plenum to pull the desired amount of outdoor air in through the ventilation air duct and into the return plenum. Then the central system air handler distributes the ventilation air to all rooms in the dwelling. Also, a damper and controls must be installed that ensure the air handler delivers the required ventilation airflow regardless of the size of the heating or cooling load.
(Excerpted from the CEC Title 24 Residential Compliance Manual)