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A return air grille is a connection to ductwork that allows air to return to a heating and cooling system. Return air openings are typically covered with grillwork that serves a number of different functions. A variety of companies make coverings for these openings that people can use to replace existing covers or can install with a brand new system. These products are available through catalogs, hardware stores, and contractors, as well as manufacturers of ducting systems.
In a heating and cooling system, the central furnace or air conditioner pushes air out through a system of ducts into the rooms of a structure for temperature control. It also pulls air in through return ductwork. The air sucked into the system is heated or cooled as needed and redistributed. Essentially, the system acts as a pump, circulating room air through a heating or cooling chamber to create a stable and consistent temperature in the structure.
The return air grille covers a register that allows air to flow into the heating and cooling system. Most grills are adjustable, allowing people to shut a room off so the furnace cannot pull air out of it. The amount of air allowed through the air grille can also be moderated, as for example if people want more cold air pulled out of downstairs rooms in the winter and less of the hot air upstairs pulled through the heater.
Return air grilles also cover the ductwork so people do not have to look at it, and prevent large objects from entering the ducts, where in addition to being lost, they could also damage the heating and cooling system. A return air grille is often fitted with a filter to trap smaller particulate materials before they have a chance to get into the ductwork. This limits the amount of cleaning needed and also keeps the system running smoothly, reducing the risk of clogs caused by dust, pet hair, and other materials.
A return vent may be located on the wall or the floor, depending on the system. It is important to make sure that return vents are covered for safety and that the return air grille is periodically lifted and cleaned, along with the filter, to prevent dirt from entering the heating and cooling system. People who are not sure about how to do this can consult a heating and cooling professional for advice on maintaining their ductwork to extend the life of their climate control system.
@Melonlity -- I had a heating and air guy tell me the same thing last summer when he was fixing my central unit. Now, mine has two air filters. One is behind the return air grille and the other is on the other side of the unit. He told me that design means the unit pulls in a lot of air and, as such, I should replace the filters monthly.
What if the filters are rated for three months and cost a lot? He said that doesn't matter. Go for monthly. His advice was to get moderately priced filters, buy in bulk and make sure to swap in new ones at the first of every month (just because it is
easier to keep up with that task if you do it at the first of every month).
That guy pointed out that simply keeping those filters changed will add years to the life of a central unit. Good advice. What is interesting is that he had nothing to say about that return air grille. In his mind, it appeared to be just the thing to hold the filter against the system.
See that filter on the other side of that return air grille? One of the main reasons furnaces/air conditioners break down is because people don't replace them often enough. If those are not replaced, they do not filter crud out of the air and that stuff can clog up your system.
For example, if you have cooling coils covered with lint, then you can't efficiently cool your home. How does that lint get in there? Usually because the filters are too full of junk to filter out anything. And, of course, you can get so much lint built up in your system that it can't suck in air, could possibly catch fire or all sorts of awful things.