When Should You Change Your Air Filter with a MERV Rating?

MERV ratings are used to measure the efficiency of air filters. The average MERV 5-10 efficiency range typically requires filter changes every two to three months. However, this average range can vary depending on other factors and the filtering material. Air filters with a MERV 11 rating or higher usually need to be replaced every three to six months.

So when should you replace air filters? Generally, it's best to change MERV 13 filters every 30 or 90 days, depending on use and other factors. While some larger 4-fold filters can last up to six months between changes, the exact timeline depends on a variety of factors, such as the humidity level in your area, whether there are any wildfires, if you have pets or smokers in your home, or if anyone in your household has chronic allergies or asthma. To ensure that your filter is working properly, it's important to periodically inspect it for any signs of wear and tear, such as dark deposits, pet hair, and visible signs of other household irritants. For allergy sufferers, it's essential to change the air filter more often. We recommend changing the filter every 30-45 days.

A general rule of thumb for pleated air filters (such as those made by FilterBuy) is to change them every 90 days. As the filter traps more dirt, dust, and allergens from the air, its efficiency decreases. A dirty air filter restricts air flow, leading to poor air quality, increased energy bills and, over time, causing the system to fail. If you have an asthmatic or allergic person at home, change the filter every 6 weeks to ensure optimal indoor air quality. To ensure that your family is safe from germs and other potentially harmful air particles, you should replace the filter more often. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) created a standard known as the MERV classification system which helps consumers select an air filter that fits their needs.

When in doubt, consult your air conditioning unit's owner's manual or a local airline representative to determine which MERV rating is right for your home. Pleated air filters trap up to 70% of particles between 3.0 and 10 microns in size and up to 20% of particles in size from 1.0 to 3.0 microns (these filters are not effective enough for smaller particles of 0.3 to 1.0 microns). Air filters are usually made of spun fiberglass (the same that forms the insulation of the attic) or of pleated paper framed with cardboard for greater stability and rigidity. If there is a layer of visible dirt that covers most of the surface of the filter and is thick enough to hide the filter material itself, it is a sign that the filter has been in the air conditioning system for too long. Yes, changing the filter has several effects on the ability of the air conditioning system to cool the house and on overall air quality. Any use will cause a certain amount of dirt to be trapped in the air filter; after all, that's its job. Pleated air filters are also disposable but they are usually more efficient than fiberglass and can last longer.

The only type of filters that trap allergens and spores are high-energy particulate air (HEPA) filters.