A return wall supplies fresh air to a building’s forced-air heating system, ensuring complete combustion of fuel and circulating air. It is a passive but critical part of building design, drawing air through internal spaces between studs. Homeowners should maintain return wall channels and avoid damaging them.
A “return wall” is a term used in the construction industry and refers to a wall through which fresh air or ambient air is drawn into a forced air circulation system. It supplies oxygen to ensure complete combustion of the fuel and circulates the air throughout the building. This allows the air to warm up or cool down with each pass.
Return walls play a passive but critical role in building design. In a building’s forced-air heating system that burns oil, natural gas, coal, or other carbon-based fuels, oxygen is required for combustion. With modern construction technologies, buildings are often sealed off from fresh outside air. If the fuel is completely burned, as it will be when there is an excess of oxygen, the carbon byproduct is carbon dioxide. In incomplete combustion, carbon monoxide is produced and is deadly to humans and pets, so it is important to supply fresh air to your oven whenever it is in use.
In residences, a passive system is employed to supply fresh air to the oven. There are no fans pushing fresh air into the system. Instead, fresh air is drawn into the furnace through the internal spaces between the studs of short sections of particular walls. These are the return walls.
The return wall differs from the adjacent wall section in that it is open at the top or bottom where the framing is located, not on the outside where it looks into the room. There it connects to a distribution system, such as pipes from floors above or below it, or both. Some ducts will connect with vents in the attic or basement to bring in outside air and oxygen. Other ductwork will connect with grilles in the return walls to circulate the air around the room. Circulation is necessary to avoid a “stale” feeling and to allow air to be exposed to the heating or cooling elements of the system and thus raise or lower the room temperature.
From a homeowner’s perspective, it’s important to know where the return walls are. They can be found if you search the grates at the top or bottom of the room’s walls. A return wall should be left intact. Small holes such as those caused by hanging pictures on the outside surface of the wall are not harmful. The back wall, however, isn’t the place to build a corner or hang a structure between studs like a bathroom vanity.
It is important that return wall channels are maintained so that the system has the mechanical ability to draw air. One can imagine the suction capacity required to draw fluid through a small diameter straw versus a large diameter straw. If the straw is split to the side, it cannot be used at all. If a return wall is removed, an alternative route for the air to circulate must be found.
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