Aprilaire Model 8126 Ventilation Control System continuously monitors indoor relative humidity, outdoor temperature and a user-adjusted timer setting. The indoor relative humidity is monitored to help prevent high humidity conditions inside homes. The Aprilaire ventilation Controller will not open the damper to outside air if there is a chance of raising the humidity inside the house to high levels. The Aprilaire Ventilation Controller is designed to prevent indoor relative humidity levels from increasing beyond 60% due to ventilation. If the outdoor air temperature is below 0 degrees F or above 100 degrees F, the motorized, normally-closed damper to the outside wall will not open. Includes electric damper, 8120 controller, 8052 outdoor air sensor, and transformer.