In general, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days or 3 months. This may vary depending on the location of your home, if you have pets, and the age of your system and equipment. The only way to determine how often you need to change your air filter is to perform a visual inspection of the filter every month. After a few months, you'll get an idea of how quickly it gets dirty and if you need to re-evaluate due to a new pet or poor outdoor air quality.
A general rule of thumb for pleated air filters (such as those manufactured by FilterBuy) is to replace the filter every 90 days. As the filter traps more dirt, dust, and allergens from the air, its efficiency decreases. Factors such as the location of your home, the age of your system, and whether or not you have pets can affect how often you need to change your air filter. The filter collects dust and debris only when the system is operating.
The more it works, the faster the filter picks up dirt. During a cold winter or hot summer, a furnace filter will need to be changed more often than during milder seasons. On the other hand, AC mode also causes the filter to get dirty. If you have pets, their hair fibers are large compared to dust and dirt that normally trap the filter.
This means they clog the filter and block airflow quickly. If someone in your household has asthma, severe allergies, or difficulty breathing for any reason, a coarse-media filter (MERV 11 or higher) or an electronic air filter is best for providing clean air. Cheap fiberglass filters require less frequent replacement than pleated filters. However, some sites get this exactly the other way around, claiming that thicker filters can last longer between changes - which goes against the design of the filters.
Coarse-media filters trap more and smaller dust particles, so they obviously clog up faster than slim fiberglass filters that don't trap as much dirt and debris. Some filters can be cleaned with a nylon brush and placed back in the oven or air controller instead of replacing them. Cleaning should be done outside or in a garage to keep dust and dirt out of your home. If removing dirt with a brush instead of replacing the media filter, be sure to change the filter after two or three cleanings - as brush cleaning will not remove enough deeply embedded dirt and debris. In larger homes, more air flows through the filter than in smaller houses. Because the air carries dust, pet hair, and other debris, the filter will get dirty more quickly in a system that serves a large house.
Some homeowners use continuous fan mode - where the fan works all the time until it is turned off - which requires changing the filter more frequently. To determine when to change your air filter, inspect it every month and listen for wheezing even when it is clean. This sound will worsen when the filter is dirty as it blocks airflow to the system. Know your system and its sounds so you can identify what noises indicate a problem. In summary, most air filters need to be changed every 90 days on average. Factors such as location, age of system, pets in household, and continuous fan mode can affect how often you need to change your air filter.
If someone in your household has asthma or severe allergies, use a coarse-media or electronic air filter for clean air.