06/07/2026
Myth : Closing vents in unused rooms save energy and pushes air to room that wont cool properly.
Fact: Your blower is sized for the full duct system. Close vents and pressure spikes upstream, pushing conditioned air through every seam and joint in the ducts. Lawrence Berkeley National Laboratory tested four configurations and found energy use rose between 5 and 25%, not fell.
It also freezes coils. Restricted return airflow drops evaporator temperature below 32F, ice forms, and the unit fails on a 95-degree afternoon. That is the most common July service call.
Keep every vent open. Use a balancing damper at the trunk line if one room runs hot, and shut interior doors only when the AC is off
