Like many hard-working citizens, you have bills to balance. If there’s a certain room you notice hardly is ever occupied, you think, “Why not just close off the vents there?” Well, hold your horses, because the air is not quite the straightforward element that it may seem at first blush.
In reality, this can actually backfire, putting a lot of unbalanced pressure on your HVAC system and running your bill even higher.
In this article, we’ll break down how central HVAC systems work, what actually happens when you close vents, and whether there are any situations where a vent closure could indeed prove a wise move. Then we’ll provide some alternative ideas to achieve better energy efficiency.
The Logic Behind Closing Vents
It’s fairly common for a family or a couple to have a guest bedroom, a storage room, or a basement that mostly just collects cobwebs. It makes sense – just shut off the airflow there and save money. After all, turning off the lights in an empty room or unplugging your blender while you’re not using it drops the output and electricity usage, right?
We think of airflow in our homes a lot of the time as like water in a pipe. If you close one valve, more water (in this case, air) will flow elsewhere. So by that logic, closing a vent in the guest room should thrust more conditioned air to the living room or master bedroom.
This line of thinking is further reinforced by old habits and outdated heating systems, such as wood stoves or radiators, where closing doors and isolating rooms could actually make a difference in how heat was distributed and contained. Sadly, the real-world impact on energy use today is not so straightforward.
Myths vs. Reality: Why the “Common Sense” Idea Doesn’t Hold Up
Square one is gaining a picture of how HVAC systems are actually designed to work. Most homes in the U.S. use a forced-air HVAC system, which relies on a blower to push heated or cooled air through a network of ducts. These ducts lead to supply vents in different rooms of a home.
After circulating the space, the air is pulled back into the system via return ducts to be reconditioned and recirculated. This cycle continues on and on and relies on a carefully balanced airflow to operate with efficiency.
The truth is HVAC systems are designed for whole-house airflow.
As any HVAC professional will tell you, residential HVAC systems are engineered for the entire square footage of a home. That means that an AC or a furnace is sized to heat or cool the full volume of air in the house at once, regardless of whether every room is occupied.
The system isn’t smart enough to know that one room is “off-limits”, because the vent is closed. It will produce the same amount of air and pressure, expecting all vents to remain open and gain air.
AIrflow Disruption
So when you close a vent, you’re in reality not cutting back the production of that air, you’re just cutting off its path. At that point, the air has to go somewhere, and it often ends up increasing the pressure within the ductwork.
That elevated pressure can cause air to leak through the ducts’ seams. This is a relevant thing in older homes in particular, especially if it hasn’t been professionally sealed.
When airflow is restricted by closed vents, the blower fan has to work harder to push air through the remaining open vents. In variable-speed blower systems, the fan may adjust and compensate slightly, but this still results in added wear and tear.
In systems with single speed blowers (more common), the fan continues to run at full speed, straining against the restricted airflow.
What this means is:
- more energy generated, not less;
- a shortening of the equipment’s lifespan;
- mechanical stress;
- poor indoor air quality;
- uncomfortable temperature imbalances.
You will have some rooms experiencing too much airflow while others won’t receive enough. So You’re thereby disrupting the system’s equilibrium and rendering it less efficient.
Role of Return Air
This is another detail that people sleep on. If you close a supply vent to a certain room but not the return vent, or if there’s a shared central return, you create a pressure imbalance. As a result, you can end up pulling unconditioned air or air from wall cavities or your attic into a particular room – not the type of air you necessarily want filling a room.
On top of that, it won’t fit the optimal efficiency. There’s even the possibility of backdraft combustion like water heaters or gas furnaces drawing carbon monoxide into the home.
Exceptions
That said, there are still some exceptions where if done safely and effectively, closing traditional HVAC vents could work.
- Zoned HVAC systems which work independently. This is actually the intent of these rooms, and it does save energy.
- Smart vents with automated control: these use sensors and automated controls to open and close vents based on room temperature, occupancy, and user settings.
- If extremely necessary, such as in situations where you are performing a home renovation and you need to keep dust from circulating. However, in this case, close only one or two vents, not several. Monitor how your system responds. And then reopen the vent as soon as possible
- Small homes with oversized systems.
Better Energy-Saving Alternatives
If your goal is to reduce your energy bill and make your HVAC system more efficient, there are more effective and safer ways to achieve that than by closing your vents.
- Seal and insulate your ductwork: leaky ducts are one of the biggest energy wasters in residential homes. According to the U.S. Department of Energy, as much as 20-30% of air moving through a duct system is lost due to holes and poorly connected joints. Sealing your ductwork with mastic or foil-backed tape and adding insulation such as spray foam in unconditioned spaces can work wonders.
- Upgrade your thermostat: installing a programmable or smart thermostat allows you to adjust the temperature automatically based on your schedule. You can set the system to reduce heating or cooling while you’re at work or asleep and return to a comfortable temperature before you arrive home. Many of them learn your habits and tailor themselves to your lifestyle. This doesn’t require any of your own input. Smart thermostats help you save on your power bill in an extensive range of innovative ways.
- Using ceiling fans and ventilation wisely: these don’t lower a room’s temperature, but they help circulate air, making you feel cooler in the summer. This allows you to raise your thermostat setting by a few degrees without sacrificing comfort. Also, use exhaust fans in kitchens and bathrooms sparingly. These pull out conditioned air, which increases HVAC usage.
- Regular HVAC maintenance: Dirty filters, clogged coils, and poorly calibrated thermostats all reduce system efficiency. Schedule seasonal HVAC tune-ups with a licensed technician to keep everything running smoothly. Replacing your filters every 1-3 months alone can improve airflow and reduce strain.
