An air return duct is basically a concealed air passageway in a home or other building that acts as a channel for pumping air out of an enclosed room and into the air conditioning or central heating system. These ducts typically start with vent grates in the wall, on the ceiling, or in the floor. Where exactly these vents are located is usually a matter of whether the system is focusing on heating, cooling, or both. Different structures have different ducting capabilities, but builders and contractors often try to put these sorts of channels near doors and windows to maximize their effectiveness. Sometimes these ducts share the job of air input, but not always. A lot depends on how the building was constructed and how difficult it is to heat or cool.
Location and Main Goals
Return ducts are an integral part of nearly all heating, ventilating and air conditioning (HVAC) systems. Generally, HVAC systems use a forced air process that blows either heat or air conditioning through ductwork into a home or business. Return ducts are usually located either in a hallway or in the ceiling, and their purpose is to extract air from a room and recycle it through the system where it will be further conditioned, either through heating or cooling.
The main thing this duct does is pull air out of a room. In the summer it will pull air that is cold, whereas in the winter it will pull air that is hot and humid. In most cases, different ducts will re-circulate warmed or cooled air to bring the building to the optimal temperature.
How the Larger System Works
Most central air and heat systems have a large condenser unit that is outdoors and a smaller coil that is located indoors, usually tucked away in a closet or utility room. Together, these two components can both heat and cool a building by controlling the air that flows to various rooms through a series of ducts.
In the summer, the return duct removes warm air from inside and transports it to the outside to be conditioned. The ducts through which the air travels are part of a sealed system that usually is located in the attic for structures with slabs, or under the floors on structures that are raised off the ground. These sorts of systems can’t really work without ducts; the ducts give air a passage through which it can flow to reach the outdoor components, undergo the conditioning process, and return to the building. Once back in the building, the air is usually distributed by a fan through registers into the rooms.
HVAC systems typically use a refrigerant to cool the air by carrying the heat outside to the condenser. The compressor in the outside unit compresses the refrigerant into a high-pressure gas. Once the gas travels through the coil and on to the outdoors, it loses heat and transforms into a liquid. It then enters the evaporator coil and expands into a low-temperature gas to absorb heat that enters into the system from the return duct. This process repeats itself until the temperature that is set on the thermostat is reached.
Importance of Good Sealing
The importance of a sealed HVAC duct system can be attributed to the temperature of the air that is extracted by the return duct. In nearly all cases, warmer air rises to the ceiling and colder air remains closer to the floor. In the case of cooling, the air return duct provides circulation of cold air as it pulls the cooler air upward, passing through the warm air that is closer to the ceiling. If there is a leak in the ductwork in any portion of the system, it could pull in unconditioned air, which will take more time and electricity to effectively condition. This usually causes the HVAC system to run longer and use more electricity to achieve the desired temperature.
Common Problems
Air return ducts can take up a lot of space, though when they’re built alongside a house or other structure they’re usually concealed within crawlspaces or behind walls. Retrofitting an existing building with an HVAC system can be troubling, at least when it comes to finding a place for all of the ductwork. Creative builders are often able to tuck these into existing spaces, and many can help redesign rooms so that a bump-out in the corner or in a closet isn’t as noticeable as it might otherwise be.
Trouble with proper temperature might be a sealant problem, but it could also be an issue with vent locations and overall force of the suction. Getting a professional to rework some aspects of the airflow can help ensure that as much is being pulled out as is pumping in. Homeowners often also find that the air return duct works more efficiently with clean filters. Experts usually recommend replacing the filters at least seasonally, though monthly or bi-weekly may be needed for people with a lot of pets or environmental dust.