Closing supply vents throws your
Reduced efficiency: Your HVAC system will work less efficiently if you block a return air vent. This will make the units use more energy and will raise your utility costs.
As conditioned air is pushed in, the air already in the home needs a place to escape. Return air vents serve this purpose by helping to pull in the air and putting it back into the system. This is what maintains proper air pressure in a home.
Blocked vents increase air pressure in your ductwork, which can create cracks and leaks. Clear vents ensure every room in your home gets good circulation so your system can work as designed. Have a piece of furniture sitting over a vent? Try using an inexpensive vent extender to direct air out into the room.
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.
You most likely thought covering your air vents would certainly save you energy, but it does the opposite. Considering that this could damage your cooling and heating system, fractures and other damage could allow air to leave your air ducts and cost you much more in energy bills.
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.
A build up of pressure can be caused by covered vents. This could lead to a cracked heat exchanger which in turn can lead to leaking carbon monoxide. Covering your vents can damage your HVAC system and cause cracks that could allow air to escape your ducts. This can lead to higher energy bills.
Contrary to what most people think, closing the vents in a room doesn't divert that air to other rooms. What's actually happening is that air will leak from the ductwork, sending cool air into areas such as interior walls and attic spaces.
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.
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.
Due in large part to the short cycling issues mentioned above, components on an oversized heating and/or air conditioning systems are more likely to fail sooner than those on a properly sized system. As a result, you may end up having to replace your HVAC system sooner than expected.
EXPERT RECOMMENDATION: If you want to try to balance the airflow throughout your home, you should not close vents completely; HOWEVER, you can close them slightly (not more than 75% closed) to help distribute air better to the areas that need it most.
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.
Closing supply vents throws your heating and cooling system off balance, creates airflow problems, and makes the system work harder. That's why it's better to keep all the vents open for optimized airflow and energy efficiency.
Blocked vents force your HVAC system to operate under increased pressure. This strain can lead to premature wear and tear on the equipment, reducing its lifespan and potentially resulting in costly repairs or replacements.
The incessant heat and humidity will cause wooden furniture to expand and warp. The same factors can create a mold and mildew problem for fabric or leather furniture. And while it is unlikely, blocking an air vent does create an additional fire hazard.
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.
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.
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.
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.
Vent covers: Each vent should have a properly fitted vent cover at the end. This not only prevents the vent from sucking in dust and other debris, it also helps blend vents into your decor and even creates optimized airflow in and out of the vent.
I'd suggest that screwing a thin timber board, cut to the same size as the vent, over the larger exterior holes would be the most straightforward solution. A neat solution for the internal vent would be to remove the cover, clean the inside with alcohol and then adhere some adhesive film over the holes.