What’s an air return duct?

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Air return ducts are hidden passages that extract air from a room and recycle it through central heating or cooling systems. They are usually located in corridors or ceilings and should be sealed to prevent unconditioned air from entering. Proper vent locations and clean filters are also important for efficient operation.

An air return duct is basically a hidden air passage in a house or other building that acts as a conduit to pump air from an enclosed room and into the central air conditioning or heating system. These ducts typically begin with vent grilles in the wall, ceiling, or floor. The exact location of these vents usually depends on whether the system focuses on heating, cooling, or both. Different structures have different duct capacities, but builders and contractors often look to place these types of ducts near doors and windows to maximize their effectiveness. Sometimes these ducts share the job of taking in the air, but not always. A lot depends on how the building was constructed and how difficult it is to heat or cool.

Position and main objectives

Return ducts are an integral part of almost all heating, ventilation and air conditioning (HVAC) systems. Typically, HVAC systems use a forced-air process that blows heat or conditioned air through ductwork into a home or business. Return ducts are usually located either in a corridor or in the ceiling, and their purpose is to extract the air from a room and recycle it through the system where it will be further conditioned, either by heating or cooling.

The main thing this duct does is pull air out of a room. In summer it will draw cold air, while in winter it will draw warm and humid air. In most cases, different ducts will recirculate warm or cooled air to bring the building up to the optimum temperature.

How the bigger system works
Most central air and heating systems have a large condensing unit that sits outdoors and a smaller coil that sits indoors, usually hidden away in a closet or utility room. Together, these two components can both heat and cool a building by controlling the air flowing into the various rooms through a series of ducts.

In summer, the return duct draws the hot air from inside and carries it outside to be conditioned. The ducts through which the air passes are part of a sealed system that is usually found in the attic for structures with attics, or under the floor for structures raised above the ground. These types of systems can’t really function without conduits; the ducts give the air a passage through which it can flow to reach the external components, undergo the conditioning process and return to the building. Once back in the building, the air is usually distributed by a fan via registers into the rooms.

HVAC systems typically use a refrigerant to cool the air by carrying the heat out to the condenser. The compressor in the outdoor unit compresses the refrigerant into a high pressure gas. Once the gas travels through the coil to the outside, it loses heat and turns into a liquid. Then it enters the evaporator coil and expands into a low temperature gas to absorb the heat entering the system from the return pipe. This process is repeated until the temperature set on the thermostat is reached.
Importance of a good seal
The importance of a sealed HVAC duct system can be attributed to the temperature of the air that is extracted from the return duct. In almost all cases, the warmer air rises to the ceiling and the cooler air stays closer to the floor. When cooling, the return air duct circulates the cold air as it draws the cooler air upwards, passing through the warm air closest to the ceiling. If there’s a leak in the ducts anywhere in the system, it could be sucking in unconditioned air, which will require more time and electricity to effectively condition. This usually causes the HVAC system to run longer and use more electricity to reach the desired temperature.

Common problems
Return air ducts can take up a lot of space, although when built next to a house or other structure they are usually hidden within crawl spaces or behind walls. Retrofitting an existing building with an HVAC system can be problematic, at least when it comes to finding a place for all the ductwork. Creative builders are often able to fit them into existing spaces, and many can help redesign rooms so that a bump in the corner or in a closet isn’t as obvious as it might otherwise be.
The problem with the correct temperature could be a sealant issue, but it could also be a problem with the vent locations and the overall strength of the suction. Getting a professional to rework some aspects of the airflow can help ensure that as much is being pulled out as it is being pumped. Homeowners also often find that the return air duct works more efficiently with clean filters. Experts usually recommend replacing filters at least seasonally, though monthly or biweekly may be necessary for people with lots of pets or environmental dust.

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