How to Close Off Air Conditioning Vents

The debate on whether you should open your AC vents 24/7 or occasionally close them when it’s necessary rages on.

In one corner is a group that believes closing vents is a no-no and in the other is another group that believes you should occasionally close some vents to save energy which in turn lowers your energy bills.

So, who’s right and who’s wrong? And, suppose you’re allowed to shut some air vents occasionally, which vents should you close, when should you close them, and how do you close an AC vent?

This guide answers these and many other related questions.

The most straightforward way to close vents on your air conditioning unit or furnace is to locate the open/close switch or dial on the ent and toggle it appropriately. Rectangular and square vents typically have a switch on one of the sides while circular vents have a dial in the center.

Should You Close Cooling System Air Vents?

No, it’s rarely a good idea to completely shut AC vents. Closing the vents creates endless challenges, many of which can make your home uncomfortable and affect your health.

Perhaps you’d appreciate this advice better with a basic understanding of how an air conditioner (and even the heating system) works.

The majority of air conditioners are closed-loop systems that recycle indoor air, filtering the air each time it re-enters the AC to maintain optimal indoor air quality.

In short, stale, warm heated air from one or more rooms flows into the AC through return vents. However, the heat is extracted as it flows past cold evaporator coils in the air handler. Then the now-cold air returns to your home via the supply vents while the heat is disposed of outside the house via a heat exchanger.

The bottom line is that it’s an air-tight system. Modern homes have fresh air intake vents that bring in new air from outside the house. However, the new air only forms a small fraction of your indoor airflow. Moreover, as we’ve mentioned, not all homes have fresh air intake vents.

Now, imagine closing some of the air vents! You may bring the entire air conditioning process to a halt. Alternatively, closing the vents can significantly sabotage the process, resulting in poor conditioning outcomes. When you close any of your HVAC system’s registers, condensation occurs due to lower surface temperatures resulting is mildew and mold growth.

Should You Close Vents in Unused Rooms?

The short answer is – NO. A few people may argue that conditioning rooms that are unused amounts to energy waste – and you’re right to a degree. However, the benefits of running the AC in these rooms far outweigh the downsides.

The first thing you must remember is that HVAC systems are sized to serve the entire home. Therefore, whenever you close off a few rooms, you’re underutilizing the AC.

As a result, you can expect faster debris and dirt buildup in the unused parts of the AC. Then, gradually, rusting and rotting may set in, and soon, you may have to replace those parts. Moreover, underutilizing the AC isn’t too different from installing an oversize unit. So, don’t be surprised if you run into short cycling issues.

Secondly and more importantly, since all the AC parts are connected, trouble in one part of the unit, even in an unused room, impacts heating and cooling systems in the rest of the home. For instance, a blocked vent in the bathroom affects cooling in the master bedroom, and, similarly, a closed vent in the kids’ bedroom impacts cooling in the kitchen.

Therefore, closing them will instantly change comfort levels in the rest of the house. You’ll instantly notice a change in indoor air quality, indoor air pressure, and so on.

Closing vents in your cooling system may lead to frozen coils, which will cause damage to the compressor in your heating or air conditioning equipment. Closing air vents in both heating and air conditioner systems causes component failure, resulting in higher system costs including system repairs and early replacement.

Does closing vents in unused rooms increase air flow?

No, it doesn’t improve air flow in the rest of the house. In fact, the opposite is often true; closing the vents may destabilize air flow patterns in your home, resulting in poor heating and cooling. Moreover, where do you expect the supply air to come from if you close the return air vent and vice versa?

Does closing the vents in unused rooms help other areas of the house?

There’s a common misconception that with vents closed your ventilation system will not be able to pump fresh air from outside into that room. Unfortunately, this isn’t entirely true. While closing vents redirects conditioned air, it may not necessarily redirect the air where you don’t want it – outside, in the attic or to a crawl space.

Should you close vents during winter?

The short answer is NO. This is never a good idea al year round. For instance, in winter, closing vents that are not oftenly used can result in cold drafts. Additionally, failure to heat or cool these rooms causes mold and mildew infestation.

What are the Benefits of Closing Air Conditioner Air Vents?

Unfortunately, there aren’t many benefits of closing air conditioner vents. However, temporarily covering or blocking the vents comes with a few benefits, including;

  • Balance indoor air pressure: Closing certain vents can help you balance overall indoor air pressure as it doesnt cause your furnace to run less. What it does is to force the same amount of air through less exits. This in turn increases the amount of pressure that is in your air duct system. This added pressure forces more air out of the leaks in your duct work than normal.
  • Prevent the loss of conditioned air: For instance, closing lower return vents in summer helps prevent the loss of conditioned cold air. It seems that summers are getting hotter. So it makes sense to figure out why your apartment is so hot and what you can do to cool it and you down.
  • Relocate vents to prevent accidents: For instance, you can close and relocate floor vents to prevent tripping accidents.

What are the Dangers of Closing Air Vents?

Permanently closing air vents anywhere in the home without a good read and proper remedy can have an overall negative impact on your life. The following are common consequences of closing air vents;

  • Inefficient cooling
  • AC system damage
  • Air pressure imbalance
  • Heating and cooling system damage (e.g., heat exchanger damage which can release the deadly carbon monoxide)
  • Reduced energy efficiency

Which HVAC System Vents Should You Close Off?

The only time you can safely close vents without adversely impacting indoor air conditions is when switching the vents as the seasons change.

For instance, at the onset of winter, you can close the upper return vents to prevent the loss of the rising warm air. Similarly, you can close lower return vents in the summer to prevent the loss of cold, conditioned air. You might also try duct sealing if your goal is to improve energy efficiency. This can reduce air loss when the heated or cooled air travels to the vents.

If the vent is a return vent, do not seal it. If you close return vents, the air pump and furnace blower will work extra hard, increasing the chances of damage.

Can you close supply vents?

No, you should never close supply vents. Granted, you can close AC supplies in winter and furnace supplies in the summer if your home has separate vents for the two HVAC appliances.

HVAC systems push heated or cooled air throughout the home with one system of ductwork (supply). Another duct system pulls air back to the heat pump or furnace, where it is heated or cooled and recirculated throughout the home.

However, most HVAC systems share return and supply vents. Closing supply vents means blocking out conditioned air from your home.

How to Close Off Return Air Vents

Whenever it becomes necessary to close air vents, the following are straightforward methods you can follow to safely shut the selected vents;

Rectangular Vents

  1. Locate the switch on the side of the vent. It’s a small lever that moves back and forth.
  2. Assuming that it’s open, check whether it’s in the up or down position.
  3. Slide the lever to the opposite to close the vent.
  4. Closed vent is if you can no longer see inside the ductwork

Circular Vents

  1. Locate the open/close dial at the center of the vent
  2. Check the position of the dial on the image provided.
  3. Rotate the dial in the opposite direction
  4. The vent is closed when you cannot see inside the ductwork

Square Vent

  1. Locate the open/close dial at the center of the vent or switch on the side of the vent
  2. Verify the position of the vent. Is it up or down; left or right?
  3. Turn the dial or switch in the opposite direction to close the vent.
  4. Verify closed vent by checking the is the registers are shut.

Other Vents Types

You can still close that floor, wall, or ceiling vent even if you cannot find the open/close dial or switch. However, you’ll need a thin sheet of insulation. You also need a utility knife or pair of scissors and a drill or screwdriver.

Of course, you also need a ladder if dealing with upper or ceiling vent. Once you have these items, proceed as follows;

  1. Access the vent (use a ladder for upper vents).
  2. Remove the vent cover where one is present.
  3. Use the marker to outline the size of insulation needed to completely cover the vent.
  4. Use a pair of scissors or a utility knife to cut the marked position of the insulation sheet.
  5. Remove the vent grille. You’ll likely need a screwdriver or drill to loosen a few screws.
  6. Place the insulation sheet over the vent opening, ensuring that it covers every millimeter of the vent close.
  7. Put the vent grille back in place and screw it tightly as you found it.
  8. Test the vent to confirm that air isn’t getting in or out.

How to Seal Air Vents

It’s always important to test your vents, open or closed vents, to make sure that they aren’t seeping air. Otherwise, seal the vent to prevent air loss or entry.

You need aluminum tape and a water-based duct sealer for this process. Gather the materials and proceed as below;

  1. Remove the vent cover and set it aside.
  2. Cut the duct tape into pieces long enough to cover each side of the vent.
  3. Carefully remove the back of the duct tape.
  4. Adhere the tape such that it spreads from the metal grille to the floor/wall/ceiling/
  5. Apply the sealer, ensuring it extends below the bottom of the tape.
  6. Restore the vent cover.

How to Block Air Vents

Blocking vent covers is similar to closing a vent cover. You can use a piece of plywood or an insulation sheet.

All you have to do is cut the plywood or insulation sheet to the size of the vent and install it between the vent hole and grille.

How to Permanently Cover Air Vents

It’s best to let an HVAC professional permanently close your air vents. However, if you must do it yourself, cut through the subfloor using a jigsaw and enlarge the section. Then rip up that enlarged section of the subfloor and replace it with plywood. Then reinforce the area with two-by-fours and replace the upper floor.

Does Closing Vents Redirect Air?

Yes, closing vents redirect air. However, it may not necessarily redirect air where you want it. For instance, it may not redirect air to unused spaces. Therefore, closing vents isn’t the best solution for redirecting air to other rooms.

Does Closing Vents Save Energy?

Have you ever wondered if you could save energy by closing vents? Closing air vents doesn’t necessarily save energy or lower energy costs. There’s a common misconception that you are doing so to save money.

However, any energy savings made by eliminating one room are lost through increased energy consumption in other rooms.

Can I Partially Close Vents?

Yes, you can partially close air vents. Indeed, partially closing air vents is much better than blocking the vents entirely. It allows you to adjust airflow in partially used rooms. But you can reopen the vents fully whenever you want.

Should I Close Basement Vents?

Yes, there’s no harm in closing a few basement vents. However, you must open vents every day or two as keeping them closed permanently can cause reduced airflow issues.

When closed vents are causing more air out of leaky ducts, this means less warmed air is being delivered to the rooms in your home. Moreover, permanently closing air vents can cause pressure imbalance and faster AC damage.

The imbalance in pressure will force it to draw air in through another, less efficient means, which can create unexpected hot and cold spots in certain rooms around the home.


How do you block an air conditioner vent?

A quick way to block off air vents is to place a heavy piece of furniture over the vent. However, if this method doesn’t work out, seal the vent with plastic sheeting. Another option is to invest in a magnetic damper. Dampers make adjusting air flow easy and even allow you to completely block the vent.

Is it okay to cover AC vents?

Simple answer No, it’s rarely a great idea to cover AC air vents as you may mess with the airflow. Moreover, covering air vents can cause indoor pressure imbalance and even affect energy efficiency. So, instead of completely closing the vent, it’s better to adjust the airflow with dampers and louvers (in the case of supply vents).

What happens if you block an AC vent?

A common danger of blocking the air vent is heat exchanger damage. The added strain can crack the exchanger. Additionally, closed vent can leave you short of cooled air or result in hot and cold spots throughout the house.

The more vents you block, the further the air will travel to circulate in the room. You may also end up with higher energy bills.

Can I block the vent in my bedroom?

Ideally, you should avoid blocking or covering air vents anywhere, including the bedroom because closing air vents can leave you short of conditioned air. Worse still, clocking bedroom vents can compromise AC function, leading to faster damage. It can also lead to higher pressure.


Generally, average home loses 20%-30% of the air passing through it’s duct system because of holes and leaks. Since your system isn’t allowed to deliver heated air to all of the rooms, it must run longer to reach your thermostats setting. This means higher utility bills.

You should avoid closing HVAC system vents as it doesn’t save energy and negatively impacts indoor airflow. Closing your vents can also lead to additional pressure, resulting in premature cooling and heating system damage. However, if you must close the vents, do it the right way. Fortunately, you now know how to seal, cover, block, and permanently seal HVAC system vents.