You should replace your air filter regularly, approximately every 30 days. Newer systems typically use pleated filters, also rectangular ones with a depth of about one inch. For those without allergies, it is recommended to replace the filter every 90 days for maximum efficiency. However, this may change depending on the location of your home, if you have pets, and the age of your system and equipment.
If you have pets in the house, it is best to change the filter every 60 days or 2 months. For households with multiple pets or people with allergies or respiratory conditions, it is recommended to change the filter every 20 to 45 days. Vacation homes or vacant homes that don't have much use can usually wait to change filters every 9-12 months. The only way to ensure 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. You will need to re-evaluate if you have a new pet or if the outdoor air quality has been poor. 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, the efficiency of the filter decreases.
The Minimum Efficiency Report Value (MERV) rating for an air filter measures how effectively the filter prevents dust and other contaminants from passing through the filter into the air stream. Children are more sensitive than adults to indoor air pollutants such as mold, dust mite debris, dander and pollen, so it is important to use quality air filters and replace them before they become clogged and dirty too much. If you live in a big city, pollutants such as smoke, dust and other debris will seep inside and clog the air filter at a much faster rate. Cats and dogs typically lose the most when winter turns to spring and summer to fall, which are key times to replace the filter. Any use will cause a certain amount of dirt to be trapped in the air filter - after all, that's its job. During these months, pollutants in your home may increase, but the air filter doesn't trap them.
It's important to note that there are high-efficiency filters that are designed to filter out small bacterial, mold, and fungal particles, but your standard MERV 8-11 filters will simply block out larger particles of dust, dirt & hair. As air moves through a building's HVAC system, air filters trap and pick up large and small particles, such as dust, allergens and microorganisms. While a filter with a higher MERV rating should last longer, it can also restrict airflow in your home. More cycles mean more filter passes and opportunities to trap contaminants, so filters typically fill faster during periods of heavy use. The general consensus is that the more you use your home, the more you need to change the air filter. Consider all factors discussed above when determining a replacement program and deciding what type and quality of filter you should use.
After a period of smoky days with poor outdoor air quality, inspect the air filter to see if it needs to be replaced.