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.
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.
A lack of return air can cause your HVAC system to overheat, leading to frequent shutdowns or overheating warnings. This overworking can also result in the air conditioner blowing warm air, especially in high temperatures.
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.
Yes, as the back pressure from the circulating fan would not allow conditioned air to enter the room. The return air duct must be larger than the inflow duct to ensure circulation back to the return air plenum to the air conditioner.
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.
If they are too small, airflow will be restricted and there will not be enough air circulation to heat or cool the inside of your home. Return air ducts must be sealed and unobstructed — Sealing return air ducts is just as important as sealing supply ducts.
Blocked outside furnace vents could cause carbon monoxide to build up in your home, potentially resulting in carbon monoxide poisoning. A blocked vent also can affect the performance of your furnace, which may not run properly or not run at all when the intake or exhaust vent is blocked.
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.
If there's not enough return air, your living room can be 10℉+ warmer or cooler than, for example, the bedrooms. Not enough return air in summer can cause rooms close to the central unit to be cooler and those farther from it to be warmer. In winter, rooms farther from the furnace can be too cool.
Hot air rises and cool air sinks. Therefore, opening the right return vents in the summer and winter significantly improves the distribution of air by your forced-air system. You'll also enjoy more even heating and cooling throughout your home. In the summer, open your high returns and close the low ones.
What room should return air ducts not be installed? Return air ducts should generally not be installed in rooms with high humidity or areas prone to moisture accumulation, such as bathrooms or kitchens.
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.
Inconsistent air temperatures throughout your home could be a sign of not enough return air. You may also notice poor indoor air quality that feels stuffy. You also may notice an increase in your utility bill since your HVAC system might be working harder due to the lack of return air.
For your furnace to run efficiently and your home to heat evenly, this airflow must be in balance. In other words, the amount of air that your furnace “breathes in” must equal the amount of air it “breathes out.” Cold air returns are what allow your furnace to “inhale” your home's air.
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.
Limited Return Air
You will want to check and ensure that the return vents throughout your vent are not blocked. If these vents are blocked, it can lead to a lack of air being pulled back into your system.
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.
While you should have a filter on your air return vent to prevent too much dust or moisture from entering your air system and recirculating back to you, you should never actually cover a return air vent. Keep furniture and even curtains at least 10” away from the vent opening in order to allow for proper air flow.
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 vents in individual rooms will not help your energy cost, but actually hurt your system. “Closing vents puts a strain on the system, which in turn causes the system to work harder,” Martin says.
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.
Mice can get into the HVAC vents through holes or cracks in the ductwork. The cracks often result from temperature changes that cause the duct material to expand and contract. In fall, when temperatures are volatile and cold winter weather is on the way, mice will be more likely to invade your home, seeking shelter.
You should never close your return vents on purpose, but it can happen accidentally.