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Partially Closing AC Vents: Things to Consider

While completely closing vents is generally frowned upon by HVAC professionals, partially closing supply air vents has received mixed reactions from experts. Some believe it is a safe way to control the temperature in your house. Others state that a lack of knowledge or professional experience makes this practice damaging to HVAC systems when attempted by homeowners. 

Here is a detailed guide to help you navigate the process of partially closing your AC vents and safe alternatives that can help you control the temperature in your home and ultimately reduce energy consumption. 


Partially closing AC vents is better than sealing them. Only close them up to 50%. Target ground floor vents and those furthest from the central unit. Only partially close a few vents. Only adjust them when required. Partially closed vents may not work as well as desired. Rather install a zoning system.

Idea Behind Partially Closing AC Vents

A popular myth among homeowners is that closing supply vents can reduce energy consumption. However, that’s a misconception that can eventually damage your HVAC system.

All HVAC systems are installed with careful consideration to the number of vents needed for effective air circulation. Thus, by messing with the established pattern of airflow, you increase the static pressure in your system.

An increased pressure level causes your system to work extra hard to make up for the sealed registers and this would eventually make your system slow down, lose its efficiency, and even fail entirely.  

Partially closing AC vents is a middle ground between the problems caused by completely closing air vents and healthy indoor air quality. 

Unlike when a vent is completely shut, partially closed vents allow air to still flow freely through the vents. That’s why it is recommended that you only shut vents between 50%-70%.

Most professionals would even advise that you shut the vents no more than 50%, preferably lower. This way, the slight change in air movement wouldn’t increase the static pressure within the unit, but it will still give you a bit more control over the temperature in a room conditioned by a central unit.

shut the vents no more than 50%, preferably lower

By partially closing the outlets farthest away from the central unit, you could even increase your energy savings. 

Things to Consider

Many HVAC specialists that are against fully closing vents agree that partially closing registers might be effective if proper precautions are taken.

industrial builder installing ventilation or air conditioning filter holder in ceiling

Margin for Error Likely to Be Small

I stated earlier that vents should be closed no more than 50-70%. However, closing the vents to the approved level could be tricky because you have no way of measuring how far you have shut the register. Thus, some homeowners could go overboard and unwittingly cause damage to the HVAC system.

The key requirement for a partially closed vent to yield the desired result is to close the vent such that the register continues to freely supply conditioned air. 

If it is shut more than it should, air will back up into the ductwork, resulting in an increase in internal pressure.  

For people without HVAC knowledge or experience, the process of partially closing vents would be a hit-or-miss procedure. That’s why it’s best to consult an HVAC specialist if you decide to partially close multiple vents in your home. 

Signs That You Have Gone Too Far

If your vents are closed more than they should, your partially sealed vents would restrict the free passage of air and might harm your HVAC system the same way a completely closed vent would. 

Should you partially shut vents more than 50%, especially if you close multiple vents, the airflow in your system might become restricted. If the airflow is restricted for a prolonged period, your air conditioning coils will freeze. 

When this happens, the efficiency of your system will be affected. Here are some signs that your vents are closed tighter than they should. 

  • Your system would produce humming sounds.
  • It would take longer to cool your home. It might even stop producing cool air altogether.
  • Warm spots around the house.
  • Water leaks.

Target Vents on Ground Floor

The natural way air moves around your home influences the operations of your HVAC system. Cold air is heavier and tends to fall while hot air rises. This is one of the reasons upper regions of houses are considerably warmer than underfloor areas like the basement

As a result, it’s recommended that you partially shut the vents on the ground floor alone. That way, the natural order is preserved, and air circulation would allow the chill from upstairs to settle downstairs, resulting in an almost even indoor temperature. 

If your system features top and bottom return vents, leave the top vent open and partially close the bottom vent in the summer months so that the system would draw air from the upper regions as cold air falls. 

Only Partially Close a Few Vents

You might be tempted to partially shut all the vents in your house since a partially closed vent isn’t likely to affect the functionality of your HVAC system. However, you mustn’t partially seal multiple vents in your house at once.

For instance, if you have 10 supply vents in your home and you close six of them 60%, the effect this would have on your system would be the same as if you completely closed four vents. 

Thus, it’s best to exercise caution while partially shutting vents. If you aren’t sure about how to go about the entire process, you can consult an HVAC specialist. 

The point is to have a safe balance between return and supply airflow. This way your air conditioner wouldn’t suffer the dangers caused by ineffective airflow.

May Not Help Other Rooms Cool Faster

Another misconception many homeowners have is that they can redirect conditioned air by closing supply vents. 

Your air conditioner can only produce a particular amount of air at a time. How much air it produces would depend on factors like the quality and specifications of the system.

By shutting or partially shutting vents, you don’t increase the amount of air available to get to some rooms; you just make it harder for the same air to reach its destination. Rooms with unsealed vents would naturally cool faster than those with partially closed registers. 

If your vents are shut tighter than they should be, they would increase the static pressure in your system, and could eventually result in duct leaks. Leaks are a menace to HVAC systems because they allow conditioned air to be lost. So, your system would have to run for longer to make up for lost air and cool your home to the desired temperature.

How to Partially Close an AC Vent

Vents come in three major designs: circular, rectangular, and square. 

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.

Circular vents feature a dial that’s usually located at the center of the vent. To partially close this type of vent, you’d have to turn the dial in an anticlockwise direction until the louvers close to your desired degree.

Rectangular vents have a switch that you can use to open or close the vent. The switch is usually at the left or right edge of the vent.

Square vents usually feature levers that you can pull to close the damper blade of the vent. 

Sometimes the switch might not be in plain view so, if you want to partially close the vent, you’d have to first remove the vent cover and then locate the control lever or switch.

Alternative or Additional Tricks

Depending on your reason for partially closing your vents, there are other alternatives that you can consider.

Adding a Zoning System to Your HVAC Unit 

This is an expensive but effective method, best suited for people who want to control the temperature in certain parts of their house. 

Most HVAC systems feature a single thermostat that controls the temperature in the entire house. But a zoning system can divide your house into “zones” and allow you to control the temperature in these areas separately.

For instance, if your bedrooms are configured to a zone and your living room to another, you can set different temperatures in both areas.  

Install Return Air Vents in the Basement 

The method of installing return air vents in the basement is only applicable if the temperature in your basement is usually frigid. It involves transferring cool air from the basement to other parts of your house by installing a return vent in the underfloor region. 

The process is complicated and is best done by an HVAC professional. For optimal performance, the vents are installed close to the basement floor.  

Ensure that AC Vents Point Upwards 

If you notice that some rooms aren’t cooling well, instead of trying to redirect the air by partially closing the registers, you should first check the placement of the vents. Positioning the vents to face the ceiling ensures that cool air isn’t lost and effectively circulates throughout the room. 

Clean Your Duct

Another factor that can influence the cooling speed of your air conditioning in certain parts of your house is dirty ducts. Dirty ducts can clog air filters and this would restrict air passage through the affected vents. 

Thus, if your primary reason behind partially closing your vents is to direct air to other rooms so that they would cool faster, then you might have to check your registers for dust buildup. 

A helpful tip is to only partially close vents whenever the need arises instead of permanently leaving them half-closed. 

Sources

https://www.libertyairac.com/why-you-shouldnt-close-vents-to-control-temperatures/

https://apollohome.com/blog/closing-air-vents/

https://www.comfortexpertsinc.com/blog/2015/august/what-happens-to-an-ac-if-it-runs-while-frozen-fo/

https://www.saveonenergy.com/learning-center/post/should-you-close-vents-in-unused-rooms/

https://bngheat.com/air-vents-okay-block/

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