Blocking air return vents causes your system to work harder, as there is less air flow to move the air back to the furnace. This continued strain on the HVAC system can lead to a decrease in performance and more HVAC repairs down the road.
You should never block your air return vents. Period.
Stagnating air: With reduced airflow, you will have stagnated air through the home. This can lead to greater levels of carbon dioxide in your air. Smells, humidity, and other airborne pollutants can also remain in the air. Reduced efficiency: Your HVAC system will work less efficiently if you block a return air vent.
In the heating cycle, blocked cold air returns can cause the heat exchanger inside the blower compartment to store too much heat and eventually crack. If the cracks are too large, the furnace can emit carbon monoxide into your home's air. Such a condition normally requires a complete system replacement.
Return vents are usually larger than supply vents and are in large rooms in the home. The return vents in your home help equalize the pressure that changes as your HVAC system heats or cools your home. These vents should never be fully closed because closing them off restricts airflow and strains the system.
Parts of Your Home Are Hotter or Colder
If there's not enough return air, your living room can be 10℉+ warmer or cooler than, for example, the bedrooms.
Even one blocked vent in the home can cause an inefficiency in air flow, which means your HVAC system will likely have to work harder to achieve the desired temperature. The result may be a home that is riddled with uneven temperatures from room to room.
The Importance of Cold Air Returns
The cold air return vents distributed throughout your home ensure that air efficiently moves in a continuous loop through your HVAC system. Without cold air returns, your system would struggle to pull in the air it needs.
The engine's combustion relies heavily on air, which mixes with fuel to generate energy. In the absence of a sufficient quantity of oxygen, an engine will not be able to generate power, and it may not even start. Whenever the air filter in your car's engine becomes too clogged, it may start to misfire.
If the return duct is too small or there are an inadequate number of return grilles, your HVAC system won't be able to return enough air to recirculate into the system. Again, it's like if you were breathing in through a straw while jogging.
Symptoms include weak airflow and uneven cooling or heating throughout your home, with some rooms feeling much cooler or warmer than others. Homeowners should regularly check vents for consistent airflow. If you notice a significant drop in air pressure or uneven temperatures, it could indicate return air issues.
Instead, there should be at least one return vent in every room, with two or three being ideal. If your house has only one return vent, this is not a problem — make sure to keep the doors open in every room so the air can circulate properly. Make sure there are no furniture, draperies, rugs, etc. blocking return vents.
You should never close your return vents on purpose, but it can happen accidentally. “It can happen from people not paying attention and throwing a rug over it or a couch that doesn't have feet, and they cover the return,” Smith says. Keep furniture at least 10 inches from return vents to allow proper airflow.
Blocked vents can pose a severe danger to your home and family. Carbon monoxide poisoning, fire hazards, and increased humidity levels are all potential risks and hazards of blocked vents. Regularly inspect and maintain your vents to ensure they function correctly and unobstructed.
Block Off the Vent: You can block the vent by placing a piece of furniture at the opening or purchasing a magnetic damper that's strong enough to stick to the steel on the wall or ceiling. Plastic sheeting can be placed over the opening as well. You can also install a vent grille filter.
By blocking it, you could strain the system or, in the case of an intake serving a furnace, cause negative pressure that causes fumes and carbon monoxide to back up.
But since a cold air intake has a direct effect on your combustion and air/fuel mix, it also impacts the function of the emissions-related equipment on your vehicle. That means installing one may put you at risk of running afoul of your state and local regulations.
Decreased Acceleration and Power
One of the first signs of a clogged intake air filter is a noticeable decrease in acceleration and power. If your car feels sluggish or struggles to pick up speed, it could be due to restricted airflow caused by a dirty filter.
Dangers of Blocked Cold Air Registers
If your HVAC system is designed this way, blocking off a single return vent can wreak havoc on the system and lead to: Pressure imbalances that let allergens and pollutants get pulled into your air supply from unconditioned areas.
Along with the air your HVAC system pushes through the ducts and vents, the air inside your home can lead to a dusty buildup — especially if your air conditioner recirculates dirt, pet fur, or other debris. This means the exterior cause of your vent's dirty situation may actually come from an interior problem.
1. Openings shall not be located less than 10 feet (3048 mm) measured in any direction from an open combustion chamber or draft hood of another appliance located in the same room or space. 2. Return air shall not be taken from a hazardous or insanitary location or a refrigeration room as defined in this code.
If you haven't suffered from moisture issues, you can attempt to close these vents. Remember that if this is a bedroom, you'll need to crack a window at night instead; otherwise, you'll have condensation running down the window by morning.
Air vents are closed or blocked by furniture, resulting in the same quantity of air being forced through your ventilation system but at a higher pressure since there are fewer options for air passage. The consequence is that your HVAC system has to work harder, reducing its lifetime.
Return air vents connect to your return ducts, and they're typically larger than supply vents. Again, depending on the design of your ductwork and home, HVAC return vent locations vary but are often in central areas, kitchens, bathrooms, and pollutant-prone areas so as to best collect stale or dirty air.