Is It Okay to Close HVAC Vents in Unused Rooms?

August 22, 2022

Heating and cooling your house makes up for about half of the total energy usage in a typical home. To save some money you may wonder if it’s okay to close air vents in unused rooms in order to direct air to other areas. Unfortunately, this may not be a good idea. Closing air vents can actually cause your HVAC system to run inefficiently, costing you more in the long run.

Why Closing Air Vents Does Not Save You Money

Your HVAC system was built to be “balanced.” This means that the ductwork was sized for the amount of air going in to equal the volume of air going out. The blower pulls air from the house through the return ducts and then pushes it back into the house through the supply ducts. Thus, closing vents changes the balance of your HVAC system.

To illustrate this, imagine you’re walking at a fast pace and breathing by inhaling through your mouth and exhaling through your nose. Now imagine you decide to close one nostril but continue to walk at the same brisk pace. You are continuing to use the same amount of air but have less pathways. You can then either use less air or put in more effort to breathe comfortably. The same goes for your HVAC system.

By closing vents, you’re not allowing your system to work less but instead increasing the pressure in your air ducts. Increased pressure in your air ducts is bad news because your blower is only designed to deliver a certain amount of air against a certain amount of pressure.

Most HVAC systems will function fine if a few vents are closed, but closing many vents at the same time is not advised. If you’re closing vents for comfort, it’s best if you only close them temporarily.

How Closing Air Vents Damages Your HVAC System

Depending on the type of blower you have (PSC being the most common), closing air vents can cause different problems:

  • Permanent Split Capacitor (PSC) Blower – Closing too many vents can cause this blower to slow down because it can’t handle the added pressure. This means your home becomes “oxygen deprived.” This could cause your air conditioner’s evaporator coil (that cools the air) to get too cold and turn into a block of ice. This will then cause liquid refrigerant to flow back into the outdoor unit’s compressor and destroy it. In the winter, the heat exchanger in your furnace could overheat and crack, risking exposure to carbon monoxide in your home.
  • Electronically Commutated Motor (ECM) Blower – This blower can adjust its speed to different conditions. Closing the air vents it will force the blower to work harder to overcome the extra pressure, resulting in a much higher energy bill.

Other Problems Caused by Closing Air Vents

  • Duct Leakage – Added pressure in the ductwork throughout your home could cause small leaks to become larger. You’ll then be paying to cool or heat your attic or crawlspace.
  • Discomfort – With a PSC blower delivering less air, your home will take much longer to cool off or heat up, causing your system to run for longer periods of time.
  • Mold Growth – When cold air and warm air meet, condensation and mold forms. For example in the summer, if there are leaks in your ductwork, the hot humid attic air mixed with the cool air conditioner air will form condensation and create mold.

It is typically best to always leave your air vents open, even in unoccupied rooms. It may sound counter-intuitive, but leaving vents open will use less energy, extend the life of your HVAC unit and save you more money in the long run.

If you find that your HVAC system isn’t working as efficiently as you like, give Reddi a call at (316) 462-2572.

We do our best to provide current and accurate information, but this content could contain errors or information that is not correct for your situation or equipment. Resources found on our website are provided as general information. Reddi Industries does not assume any liability resulting from the provided information. If you attempt to repair or modify HVAC, plumbing, electrical, or other equipment in your home or business, always consult your equipment’s operating manual first, and only do so if you are qualified.