7 Consequences of Closing Vents to Rooms You Don't Use in Winter

Wednesday, January 10th, 2018 by Joy Padgett

 I know a great number of people who close the vents and the doors to certain rooms or areas of their home during the winter in order to make the remainder of the home more comfortable and to cut down on utility bills. However, your HVAC system was designed to provide heat for your whole entire house. Shutting the vents and/or closing the doors for long periods of time, can cause issues with your HVAC system. These issues can cause unexpected HVAC service calls, system damage and health and safety issues.

First, let’s get a good basic working knowledge of the HVAC system. I’m going to keep it simple and not go into great detail, but rather give everyone a good working knowledge of HVAC systems that we can use to understand why shutting the vents in certain areas isn’t a good idea.

Are you unknowingly causing issues with your furnace?

The blower in your HVAC system pulls air from the house through the return ducts and into your system where the air is then heated and then the blower pushes it back into the house through the supply ducts. Your system is designed for the blower to push against some maximum pressure difference.

When you close vents, you make your duct system more restrictive. This changes the maximum pressure difference by increasing the pressure in your duct system. A higher pressure will cause the blower motor to ramp up in an attempt to maintain proper air flow. This translates into more energy usage, not less. On top of this, since the vast majority of duct systems aren’t sealed, more air is leaking out into the non-living space areas of your home (attics and crawl spaces). Do you really want to heat your attic and crawl space?

Woman wonders why she's heating her attic/crawl space

Since this is wintertime, let’s talk a little bit about heat. In addition to moving air, your furnace also heats the air that flows through the system. The air passes over a coil or heat exchanger and picks up heat. This means your home is not going to maintain your desired temperature and you’re not going to be comfortable.

Since most systems are fixed-capacity systems, we’ll use this as we move forward. The amount of heat the coil or heat exchanger is able to absorb is fixed. When the air flow goes down, the air is not heated as much resulting in the temperature of the coil or heat exchanger changing.

If you have low air flow over a heat pump coil in winter, you could get a really hot coil, high refrigerant pressure, and a blown compressor or refrigerant leaks. Similarly, low air flow in a furnace can get the heat exchanger hot enough to crack. A cracked heat exchanger actually allows exhaust gases to mix with your conditioned air. When that happens, your duct system can become a poison distribution system as it could be sending carbon monoxide into your home.

Are you creating a health and safety risk in your home?

Another health and safety issue that can be created by closing off vents is the promotion of condensation and mold growth. This can occur in the rooms where you closed the vents. Because closing your vents will create a different surface temperature in those rooms, condensation can form and from there mold can begin to take root, grow and spread. For those with allergies, especially sensitivities to mold, this can cause serious health hazards. On top of that, mold remediation can be expensive and intrusive.

So, from here we can identify 7 consequences that stem from closing vents off during the winter. 

  1. Increased duct leakage
  2. Lower air flow from your blower
  3. Increased energy usage
  4. Comfort problems stemming from low air flow
  5. Cracked heat exchanger requiring furnace replacement
  6. Potentially deadly carbon monoxide distribution throughout your home
  7. Condensation and mold growth

Now, if your home contains rooms or areas that just don’t stay warm in the winter, your HVAC system probably isn’t the source of your troubles. Having your system checked regularly is recommended, but we have found that the majority of our customers don’t have HVAC issues preventing them from being warm in their own home. How do I know this? Our customers tell us they started with the HVAC system as the culprit and were told the system is functioning well.

If you’ve been closing vents and blocking off certain areas of your home in an effort to stay warm, please stop and call the professionals where I work. They can uncover the real issues and provide solutions! You’ll be glad you hired them when you have the work completed on your home and notice warmer, more comfortable temperatures inside your home!

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