Heating, ventilation and air conditioning (HVAC) systems circulate conditioned air through a network of ducts that run throughout a home or building. Residential HVAC systems send air to different zones or areas within a home. Depending on the HVAC system's design, manual or automatic controls make it possible to change the airflow direction within the duct work.
Refer to your HVAC system's manual to determine the zone layout for the system. In older homes, duct lines that come off the main furnace unit deliver air to specific areas or zones within the home. Manual controls -- also known as dampers -- consist of small, hand-sized levers or valves that sit on the outside wall of a duct. Manual controls appear in the area where duct lines branch off from the main system.
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Change the direction of airflow within a duct line by turning the valve or lever on the manual control. The direction of the valve handle determines the amount of conditioned air each zone receives. Turning the handle to a position parallel with the duct line will open the damper completely. Turning the handle to a position that's perpendicular to the duct will close off the line and block any airflow. Handle positions that sit in between open and close deliver more or less conditioned air to specific zones.
Open or close the mechanical louver attached to a room's supply air register. Supply air registers control the airflow within specific rooms. Register louvers open and close vent doors and also increase or decrease the amount of air that flows into the room. Supply air registers work in addition to manual duct line dampers.
Locate the thermostat zones within the HVAC system's layout. Each zone's thermostat regulates airflow within that particular zone. The thermostat has a control switch that automatically opens and closes motorized damper doors inside each zone's duct line.
Move the thermostat control to the "On" position to activate the motorized damper control mounted on each duct. Thermostats may have additional settings that leave damper doors partially open. In effect, the thermostat settings change the airflow direction by regulating the amount of air that enters a zone. A completely closed damper allows other zones or areas within a home to receive more conditioned air.
Increase or decrease the amount of air that flows to an area with the thermostat's blower control switch. This switch activates a fan unit attached to a particular zone's duct line. The blower, in effect, increases the rate of airflow within a duct, even if the damper door is completely or partially open.
Create a balanced airflow throughout all areas of your home by determining which thermostat or manual settings deliver equal amounts of air to different zone areas.
A lack of airflow into a particular zone may indicate a failing damper motor for automatic controls or an improperly mounted lever or valve for manual controls.