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Does Closing Vents Redirect Cold Air: The Facts

Many of us have tried “life hacks” that have not actually turned out to make our lives easier. Closing some of your AC vents in unused rooms of your home seems like a life hack to make used rooms cooler and save energy. However, this is not a good idea.

Closing certain vents in your home can mess up your AC system and even create huge systemic problems with your furnace blower and thermostat. While it seems like closing vents would save you money, it actually ends up costing you in the end, and it won’t redirect the cold air as you hoped.


Closing vents in summer won’t redirect cold air to used rooms. Shut vents increase resistance in ducts and the amount of energy required to satisfy normal air supply to used rooms. Greater duct pressure creates/worsens gaps and cracks, so conditioned air is lost. The furnace blower and AC can fail.

Closing Vents in Unused Rooms Summer

Closing vents in unused rooms is intended to allow more cold air into the used rooms and, therefore, save energy since you are cooling fewer rooms. This would also save you money in theory. However, this is not the outcome that is achieved.

The HVAC system is carefully balanced to supply the whole house, and closing vents is like blocking arteries. In a cardiovascular system, a blocked artery results in the entire system shutting down. This is similar to an HVAC system.

The system is not equipped to deal with the excess pressure caused by the closed vents blocking the system, so rather than saving energy and money, it wastes them by making the system work harder to achieve the same outcome.

Closing Vents: What Actually Happens

Duct Static Pressure (Resistance) Increases

The HVAC system of a house must be expertly planned to ensure the correct amount of air gets to every room in the home. When certain vents are closed, the system is thrown out of balance.

Mature man examining an outflow air vent grid and duct to see if it needs cleaning. One guy looking into a home air duct to see how clean and healthy it is.

Within the system, there is velocity pressure and static pressure. Velocity pressure flows through the ducts in a certain direction and static pressure pushes outwards against the ducts.

When vents are closed, static pressure increases within the HVAC system, creating higher resistance to airflow.

So, while you may think that closing vents will cause more cool air to flow into the used rooms of the home, it doesn’t. Instead, more energy becomes necessary to make up for the higher static pressure, making your AC work harder to supply the normal amount of air to the used rooms, costing you more money.

Cold Air Escapes from Ductwork

Due to the higher level of pressure within the system, closing vents creates a strain on the ducts. More air means more chances for air to push through any cracks in the ducts and escape, or even to push against joins and create gaps.

After an extended period, these leaks can worsen and become a large issue that costs money to fix.

Additionally, cracks and leaks within the system will decrease efficiency. The cool air you are trying to supply rooms that are in use is partially lost into the ceiling, crawlspace, and attic. The thermostat will pick up the deficient cooling and trigger the system to work harder and/or longer to compensate.

This will also make the system much less cost-effective.

Furnace Blower Can Stop Working

While you may not realize it, the furnace and the AC are connected within the HVAC system of a home.

The furnace blower is essential to making sure your AC is running properly all summer long. Both the furnace and the AC rely on the same blower to spread air through the house; the difference is the temperature of this air.

When there is too much pressure within your HVAC system—more than it is designed to handle—it can create problems with your furnace blower.

The furnace blower is designed to move a certain amount of air into the home. When it needs to overcome excess pressure in the system, it is then going to have to work outside its limits, and it may then fail.

Watch this video for a better understanding of how the AC and the furnace blower are interconnected.

Heat and Humidity Not Removed From House

The AC evaporator is attached to the AC and furnace blower system, and its job is to remove excess moisture from the home. If the AC stops working, the AC evaporator stops working, and this leaves excess humidity in the house.

In areas where high humidity is common, the AC evaporator can serve as important a purpose as the AC system in terms of making living conditions comfortable. It serves as a built-in dehumidifier for the home.

So, if some vents are closed in your HVAC system, it can lead to a shut down of not only your AC and furnace blower but your AC evaporator as well. Your home will be hot and muggy without these assets working in the summertime.

Thermostat is Confused

A thermostat’s job is simply to read the temperature of a room and, when adjusted, tell the AC system to work harder or not as hard. With an HVAC system in disarray, the thermostat is not going to be able to do its job correctly.

With air escaping through cracks in the ductwork, certain areas of your home are not going to receive the air they need. Since the thermostat is calibrated for the pressure of the HVAC system before the closed vents, it will not be able to adjust to the leaky ductwork.

Additionally, if your thermostat is located in a room where you have closed a vent, it will read the temperature of the house as being much warmer than it actually is in used rooms and will try to compensate for this.

Air Quality in Unused Room Suffers

When you shut off the air supply to a room, it becomes subject to excessive heat and lack of air filtration. This can damage the room and items therein, but it can also reduce the quality of the air in your house. Your door is unlikely to be a perfect seal, so this air permeates the rest of the house.

Sources

https://www.osti.gov/biblio/349958-impacts-static-pressure-set-level-hvac-energy-consumption-indoor-conditions

https://www.osti.gov/biblio/349958-impacts-static-pressure-set-level-hvac-energy-consumption-indoor-conditions

https://www.energyvanguard.com/blog/can-you-save-money-by-closing-hvac-vents-in-unused-rooms/

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