Air filters keep your air conditioner clean. It’s like when you are wearing a mask to protect your lungs. The filter in your air conditioner does the same, and they have two main functions.
First it helps to improve your home’s indoor air quality. This can improve the health of your family. According to the U.S. EPA, the air inside your home can be 2 to 5 times worse than the air outside.
The second thing they do is to keep your air conditioner clean. If the dirt gets through the filter it can clog your ac unit evaporator coil. This can happen because indoor unit collects condensation and evaporator coil is wet when air conditioner is in cooling mode. Therefore, if you don’t have an air filter in your indoor unit, the dirt will collect on your ac unit’s evaporator coil.
Either way, this restricts air flow. This in turn can cause air conditioner to work harder. During cooling operation, the operating efficiency will be reduced significantly, your electric bills will go up, and it will cause more wear and tear on system parts. It is very important to keep your air filters clean.
The filter is usually located in one of the following places:
- At the central air return register, grille located in a wall or ceiling if your system uses centralized air returns instead of individual room-air return ducts. There may be several central return points, depending on the design of your system. If there are more than two, chances are the filter was placed at the air handler instead of at these grilles
- At an attic air handler, look for a slot which has a removable cover. The slot may be just an inch or so wide if 1″ thick filters are used, or it could be several inches wide if a wide high-capacity pleated or similar filter was used. The return air plenum on an attic or basement air conditioner blower unit will usually be a large metal enclosure about the same dimensions in width and height as the air conditioner blower unit itself. Look for a filter slot right where the return plenum contacts the blower fan assembly.
- At a basement air handler we also look for a filter at the return air plenum which is often next to the bottom of the air handler if the system is an “up-flow” unit (or vice versa for the less common case of return air entering at the top of the air handler and exiting at its bottom).
- Next to an electrostatic air cleaner, if your air conditioning air handler has an electrostatic air cleaner installed, look for the filter, if there is one, next to the electrostatic air cleaner. In addition, the electrostatic air cleaner, which is a type of particle incinerating filter itself, needs to be removed and cleaned periodically.
Air filters have a standard rating. This rating, minimum efficiency reporting value (MERV), is a number from 1-16. You don’t have to know all the technical details. As the number goes up the unit will stop more and smaller particles. If you decide to replace your existing air filter with one of a higher MERV rating, you should check to make sure you have sufficient airflow after you replace it. This is done by checking the temperature rise in the heating mode and the temperature drop in the cooling mode. Many air conditioners come with a washable type of filter. These will usually be made of foam. You can also use a disposable type which is normally made of fiberglass. These have a merv rating of 1 to 4. Usually you can hold those types of filters up and see through them. If that is the case, you know they are not doing their job. Another disposable type is the pleated filter. These have a merv rating of 5 to 8. These products have more surface area to catch the dirt. They also distribute the airflow more evenly. This means the fan is less likely to pull the dirt through the filter. Air filters with the higher MERV ratings are sometimes called allergy filters. Some are made of advanced materials which set up a static electrical charge. They are called electrostatic filters and are able to capture much smaller particles. Some come with an antimicrobial treatment. This prevents organisms from living on the filter when they are trapped.
Using the right air filter is only half of the answer though. If it is not replaced or cleaned often enough, your air conditioner operating efficiency will go down. This will cost you on your utility bills as well as wear and tear on the air conditioner unit. Most people, even those in the air conditioning industry, don’t change or clean their filter as often as they should. It is usually out of sight and out of mind. Most air conditioner service companies offer service contracts where they change your filter. These contracts can be expensive when you consider you can do it yourself. There are other options if you have special needs such as allergies. The ultimate filter is called a high efficiency particulate air filter (HEPA). These remove virtually everything but the replacement elements can be expensive unless you shop around.