When you have unoccupied or under-used rooms in your house, closing air vents in those rooms is an energy-saving strategy that seems to make sense. This conclusion is usually based on three false assumptions:
- Less heat going into rooms means furnace energy consumption is reduced.
- Heat obstructed by closed vents in an unoccupied room is simply redistributed to occupied rooms.
- It is only hot air, so there is no harm to equipment in shutting off the air flow.
Here are the facts countering those assumptions. Closing air vents is not recommended by HVAC experts. It does not save energy and can actually upset the supply and return airflow balance throughout the rest of the house. Closing air vents in some rooms could even damage critical furnace components. Consider the assumptions one at a time:
- A furnace has no way to know that vents in any room are open or closed. Your furnace just keeps on faithfully producing the same British Thermal Units (BTUs) of heat output—and consuming the same amount of energy—as it was designed to do. Net result: no energy savings.
- When air vents are closed, heat is not necessarily redistributed to the nearest room where vents are open. Sometimes, it is distributed into your attic, crawl space or within your interior walls. Residential ductwork is notoriously leaky and typically spills at least 20 percent of the heat it is supposed to deliver. Closing supply vents increases air pressure inside the ducts, forcing an even greater volume of heated air out through leaks into unconditioned zones of the house. To compensate for lost heating, the furnace runs longer cycles, increasing heating costs.
- Vital furnace components require a minimum return airflow volume to maintain safe internal temperature. Closing supply air vents in rooms reduces return airflow, potentially overheating the heat exchanger—the most expensive component in the system—and causing cracks to develop. A defective heat exchanger can even pose a safety hazard due to carbon monoxide (CO) infiltration.
For more effective ways to save on heating costs than closing air vents, contact the professionals at Apollo Home Heating, Cooling and Plumbing.