Many central air units have at least two filters, although you can find systems that only have one. The reason for this is that it is necessary to filter the air that travels to the air controller, as well as the air that passes through the return vents. This configuration exists for several reasons, such as the difference in lifespan of the filters and their different sizes. Technically, both components can be referred to as “ventilation grilles” because they are both places where air circulates in your home.
The key difference is that the intake grilles “draw air out of the room” and the duct grilles “push” the air conditioner into the room. You can usually see the difference visually, since the entrance grilles are larger and less numerous than those for the ducts, which are often found in every room in the house. The cabinet may be configured to accept a one- or two-inch filter. You would have to remove the side tracks to insert a two-inch size.
That was probably easy at the time of installation. A single good quality Merv 8 filter is sufficient. First of all, keep in mind that you can have more than two filters. Multi-level homes are the most likely to have these, as they often require several return ducts and may have more than one HVAC system.
Usually, each system will have at least one air filter. Therefore, your home may have air filters located on the air controller AND on the returns. You should check every possible location to ensure that you have found all your air filters. They require professional installation because the air controller usually needs to modify the duct to fit it (they are between 6 and 7 wide and do not fit in a standard filter compartment). Central air conditioners are the ideal choice for people with large homes or who want cool spaces with several rooms. Because HVAC units are often hidden in smaller, less convenient spaces, some homes are configured to place air filters in return vents.
In some cases, there may be more or less, depending on the square footage of the house or apartment and the number of floors the central air system must support. There is usually not enough volume to keep dust in the air long enough for the air conditioner inlet to act as an air purifier. From sizes to types, qualities and more, here's everything you need to know about air filters. This tip from a Houzz discussion forum is worth mentioning: if you see a return duct that can accommodate a 2- or 4-inch air filter, but that has several 1-inch filters stacked on top of each other to fit the slot, get rid of this configuration right away. The reason for replacing filters in central air systems is because they become too restrictive on air flow (CFM) or start to not work as well by letting in the same things they are trying to filter, if not replaced over time. While central air intakes also help filter contaminants to provide clean air, filters offer additional removal.
It is recommended that you look for high-efficiency particulate air filters; contact an HVAC expert if necessary. Depending on the size of your home, you may have more or fewer entry holes, but in most homes, the central air system has 2 intake openings covered with an air filter. The air controller draws air from the house through the return duct system and then blows it through the heating or cooling system and returns it to the house through the duct system. Now that you know where to look for all your replacement air filters, you're on your way to breathing better, cleaner air in your home. Over time, this will put more pressure on your entire central air unit, including the fan, cost you more money on your utilities, and can cause premature failure. Finally, placing some filters on an air filter is unlikely to be significantly noticeable during electrical use or strain on the engine, but it has a mathematical impact (it's not free).