Closing HVAC Vents In Unused Rooms

Closing air vents is a popular strategy for adjusting air flow in the home. After all, it does seem like closing vents in unused rooms would save energy and money by reducing heating and cooling costs since it is less square footage to heat or cool. However, despite this popular theory, it is actually a common misconception that closing vents in unused rooms saves energy.

Homeowners have been closing vents for decades in an attempt to redirect air away from unused spaces. The belief is that closing a vent will simply push the air onward to other parts of the home, improving energy efficiency. In fact, it can actually waste more energy than operating your system normally does. Closing vents in unused rooms saves air from entering the room, but it also pushes the excess air to other places in your home.

Regardless of how many vents you have open, the heater or air conditioner produces the same amount of air. The added pressure from closing a vent can cause air leaks in your system, causing long-term and unnecessary energy waste. Air leaks cause the unit to work harder as it tries to make your home comfortable. In addition shutting vents could damage your AC or heater, leading to inefficient operation and costly repairs.


Why Closing Vents in Unused Rooms Seems Like a Good Idea

In theory, closing vents in unused rooms seems like a good idea. By closing off the vents in a room, you would expect that cool air would skip that room and be delivered to the spaces that need it instead. As a result, your air conditioner would be able to focus its energy on only cooling rooms that you occupy, which would decrease the amount of work it would have to do. So why is this a bad idea?

While the answer is simple, the explanation why is a bit more complicated. After all, it seems like common sense that you wouldn’t want to waste conditioned air on rooms that no one is in, but this is one of those situations where what seems like common sense isn’t sensible at all.

The problem here has to do with air pressure. Your HVAC system is designed to push air through the ducts at a particular level of pressure. That design takes into account the number and placement of vents throughout your house. When you close those vents, you increase the air pressure in the ducts, sending it higher than what the system is designed for.

Imagine that you are walking at a brisk pace. You are breathing by inhaling through your mouth and exhaling through your nose. Moving air like this is how your HVAC (heating, ventilation and air conditioning) system works; the blower pulls air from the house through the return ducts and then pushes it back into the house through the supply ducts.

Now, imagine you close one of your nostrils but you continue to walk at the same pace. By doing this, you are trying to move the same amount of air but have fewer pathways to do so. So, you will need to either move less air or you put in more effort to breathe comfortably. Similarly, when you close a supply vent, you are not causing your air conditioner to work less. All you do is increase pressure in your air ducts.


What Actually Happens When You Close Vents in Unused Rooms?

The truth is that closing off the vents in unused rooms can lead to some unintended consequences. You see, air conditioners are designed to deliver a specific amount of air based on your home’s size and specifications. Supply and return vents are strategically placed so that the amount of air that comes out of your supply vents is equal to the amount of air that is sucked in by your return vents. If you close off the vents in a room, you throw off the intended pressure balance that your system is designed to operate under, which can lead to the effects below.

Nine Unintended Consequences of Closing Registers

Those who swear by the closed vent theory are obviously not looking to have adverse consequences. They are looking to save energy and money but they will likely suffer these adverse consequences if they continue closing their vents.

The first thing that happens when you close vents is that the air pressure in the duct system increases, which may give rise to these negative consequences:

  • Increased duct leakage
  • Lower air flow (with PSC blowers)
  • Increased energy use (with ECM blowers)
  • Comfort problems because of low air flow
  • Frozen air conditioner coil
  • Dead compressor
  • Cracked heat exchanger, with the potential for getting carbon monoxide in your home
  • Increased infiltration/exfiltration due to unbalanced leakage
  • Condensation and mold growth in winter due to lower surface temperatures in rooms with closed registers.


Dangers of Closing Vents in Unused Rooms

Closing air conditioning vents can cause these major problems:

  • Your System Can Break Down

Restricting airflow to your system by closing off vents can cause your air handler to overheat and your evaporator coils to freeze over. In addition, because your system has to work harder when pressure builds up inside your ducts, closing vents in unused rooms increases the chances of overstressing major components like the compressor and causing those parts to break down.


  • Increased Air Pressure

This increase in air pressure leads to a cascade of unintended effects. First of all, the ducts in most homes are unsealed. When the air pressure rises, more conditioned air leaks out of those ducts into your walls, attic and crawl space. Instead of making the system more efficient, you are now wasting energy heating or cooling those totally uninhabited parts of your home.


  • Decreased Airflow Causes Bigger Problems

If the furnace is running, decreased airflow can lead to the heat exchanger overheating. And when it overheats, that can lead to cracks. A cracked heat exchanger is not only expensive to replace, but can also allow odorless, invisible, and extremely dangerous carbon monoxide gas to leak into your home, posing a serious threat to the health and safety of your family.


  • Permanent Split Capacitor (PSC) Blower Will Slow Down

Closing vents causes this blower to slow down because it cannot overcome the extra pressure. Thus your system becomes “oxygen-deprived.”


  • Electronically Commutated Motor (ECM) Blower Will Need to Work Harder

This blower can adjust its speed to varying conditions. When you close air vents it will ramp up to overcome the extra pressure. This results in higher energy bills for you.


  • Your Energy Bills Will Be Higher

When you close off supply vents, air will build up inside of your ducts because there will be less vents available to release that air. This can raise your energy bills for a couple of different reasons. For one, the increased pressure in your ducts will make it harder for your air handler to blow air into the ducts, and the restricted airflow will cause efficiency problems similar to a dirty air filter. In addition, if your ducts have leaks, the increased pressure in your ducts will push air out of those leaks and force your system to work longer to compensate.


  • Your Home Can Encounter Comfort Issues

When you close off the supply vents in a room, the return vents in that room will attempt to suck in air from wherever it can get it. Often times this means pulling in outside air through leaks in your walls, floors and ceilings which can make your home uncomfortable.


Why Closing Vents Does Not Actually Save Energy

The balance of your HVAC unit is greatly affected when you close the vents. Since your unit was built to be balanced, the ductwork for air going in was built to match that of air going out in terms of volume. The blower sucks in air from your indoor space via the return ducts and then directs it back into your indoor space via the supply ducts.

By closing vents to save energy, you do not actually make your unit work less, but instead you increase the pressure in the ducts. Increased pressure in your ductwork causes higher energy bills since your unit now has to work harder to transport the air. Apart from the high energy bills, you may also notice your air conditioner running but not cooling as a result of the increased pressure.


How to Reduce Energy Use Without Closing Vents

If you are trying to lower your energy consumption, here are a few tips that could help you achieve this goal:

      • Check for air leaks, particularly in areas such as the attic, crawl space, windows, doors, ductwork and plumbing.
      • Add caulk to your windows and doors. This can help prevent air from escaping your house.
      • Install weather-stripping on your windows in order to keep the cold and rain out of your home.



Final Thoughts

If you want to cut off heating and cooling to certain parts of the house, the most efficient way to do so is by installing a zoned HVAC system. This will effectively cut off this portion of your ductwork from the rest of your home so you can manage it with a completely separate set of thermostat settings.

You can always count on the Aire-Tech to keep your home cool. Perhaps you need repairs, new thermostat installation, or preventative maintenance—whatever the HVAC issue is, Aire-Tech is ready to help. If your system needs repair or inspection before summer, call us on 951-926-1002. You can also visit our Contact page and complete the contact form.