Closing vents in unused rooms sounds like a simple way to save energy, but many ducted systems do not work that way. The blower and ductwork are designed around a certain airflow; raising resistance can reduce efficiency, increase noise, and worsen system balance.
The blower does not stop working because a vent is closed
In a typical central system, closing one outlet does not proportionally reduce blower or compressor energy. Some of the pressure simply rises inside the duct system.
Too many closed registers can reduce equipment airflow
Less airflow through the coil or heat exchanger can hurt performance and, on some equipment, trigger safety limits. The exact effect depends on design, but closing many registers is not the same as proper zoning.
Real savings usually come from reducing heating or cooling load
Reasonable thermostat setbacks, air sealing, insulation, and maintained filters and equipment usually have more impact. Closing a room door may help comfort, but closed registers should not be the primary energy-saving strategy.
A zoned system manages airflow by design
Zone dampers and controls coordinate which areas receive air and how the equipment responds. If parts of the home need routinely reduced conditioning, a designed zoning solution is different from manually shutting vents.
Sources
- U.S. Department of Energy — Energy Saver — Residential energy efficiency, heating and cooling, and equipment use.