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Use Caution When Closing Heating Vents In Unused Rooms

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It's no secret that heating your home in the winter can be costly. Many make the mistake of closing the vents to all unused areas of the home thinking it will save both money and energy. Surprisingly, that isn't always the case and can even lead to further problems with your furnace. To understand why, you will need a basic understanding of how your furnace and ductwork work together to heat your home.

How it Works

A professionally installed furnace is designed to draw air from your home into the return ducts and blow heated air through the supply ducts. Supply ducts are typically located in each room of the home. Because the furnace is designed to function blowing against a specific amount of pressure set by the manufacturer, it automatically regulates the speed of the air flow. While some furnace motors called electronically commutated motors (ECMs) have variable speeds, other furnace motors, referred to as permanent split capacitors (PSCs), function on a split speed. In essence, the blower takes its cues from the pressure in the ductwork. When you close the vents in your ductwork the blowing air is not able to flow out the vent, which increases the air pressure in the ductwork and alters the way your furnace functions.

Why is increased pressure a problem?

Depending on your heating system, increased pressure can have different effects.

  1. With a PSC motor, high air pressure will cause decreased airflow, as the motor continues to spin but at a lower speed. While you will still get warm air through the open vents, the decreased airflow may make it more difficult to heat your home. With an ECM motor, the motor will work harder to maintain the same airflow. This means you will continue to get warm air into your home, but your furnace will use more energy and you will pay more for heating your home.
  2. Increased pressure also contributes to heat loss from the ductwork in your home. When the warm air blows against the closed vents, some of the air will leak out of the ductwork around the joints. It is estimated that the average home loses between 25 and 40 percent of its heat through faulty ductwork. Closing vents may cause that heat loss to skyrocket. This lost heat pools in unused areas of your home, like the attic or inside walls. It can also cause an imbalance of air pressure in the home, as rooms with open vents will have a higher air pressure than rooms where the vents are closed off. Because air pressure flows from the area with the highest pressure to the lowest pressure, this may set the stage for problems with air leaks in your home. It may cause cold air from the outside to leak into rooms with closed vents, while warm air may leak outside around windows or doors in rooms where the vents are open.
  3. Increased air pressure can cause the heat exchanger to heat up and crack. Not only will you face the expense of repairing the furnace, a cracked heat exchanger allows exhaust to the enter the home. This means your blower may channel carbon monoxide throughout the house putting your family at risk.

Is it ever safe to close the vents?

Most supply vents do have an open and closed position that can be used to direct the amount of heat in the room. Closing off one or two vents in the house typically does not cause a problem as long as your ductwork is tight and secure, explains Energy Vanguard. However, it further warns that closing even one vent can be risky business if your ductwork is old and leaky.

Keeping your family warm while saving energy is always desired, but closing the vents to unused rooms isn't likely to accomplish that. Have your heating system inspected and serviced before the heating season begins to keep it running efficiently. Your furnace repair contractor can also check the ductwork and replace or repair faulty connections to reduce the amount of heat loss in the winter. Cleaning or replacing the filter with all improve airflow and keep your furnace running efficiently and save on heating costs.


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