It seems obvious to close HVAC registers when indoor temperature control is an issue. You can keep the rest of the house comfortable and save money by not wasting heating and cooling in rooms you don’t need. Unfortunately, it’s not that easy. HVAC units and ductwork systems are designed to deliver a specific volume of air to each and every room based on its square footage. One or more registers can affect that careful equilibrium. HVAC systems don’t know whether all registers are open. Until the thermostat setting is reached, it produces the same amount of heated or cooled air and consumes the same amount of energy. Each room’s supply air volume is controlled by internal dampers inside the branch ducts. In this way, consistent temperatures are maintained whether a room is close to or far from the blower. When one or more supply registers are closed, airflow balance and temperatures are disrupted. Rooms closest to the blower may receive too much airflow, while rooms farther away may not. Closing supply vents increases static pressure inside the supply ductwork, which in turn stresses the system blower, potentially leading to a shorter service life of that component.