How Often Do You Really Need to Change a Furnace Air Filter?

There are several factors that go into determining the expected life span of a furnace filter. Obviously, if the filter looks dirty, you should swap it out. But what if it looks relatively clean? Since hair, pollen and airborne particulates aren’t always visible to the human eye, you can’t always trust your eyesight to help you determine whether your need a new filter.

Even if the filter seems fine, it may only be working at around 50 percent, which could strain your HVAC system and reduce the air quality in your home. To determine whether your furnace air filter needs a replacement, ask yourself the following questions:

Do you have allergies? If you or someone in your family suffers from allergies, you should swap out your filter more often than recommended. The dirtier a filter gets, the less effective it is at trapping allergens within your home. Check the manufacturer’s recommendations, and cut them in half to ensure that your air-quality is optimal. You should also monitor pollen counts and keep your windows and doors shut during peak times. This way, fewer allergens will enter your home and find their way into your HVAC system.

Do you have pets? If you have cats or dogs, you will want to change your furnace filter more often. Pet hair and dander can build up in a home and find its way into your HVAC system. A high quality filter is essential for protecting your system in addition to removing these particles from the air you breathe. As with pollen, if the filter gets dirty or clogged, it won’t be able to trap pet hair and dander as efficiently. If you have pets, change your filters more often. If you have several pets, consider investing in an air purifier to take some of the burden off your furnace filter.

What type of furnace filter do you have? Filters vary in several key ways, depending on the system and price. Fortunately, they almost always include factory recommendations on how often they should be changed. Some will require a replacement every month, while others can go as long as six months. In most cases, cheaper air filters will need to be changed more frequently, because they are either thinner or comprised of less effective material. You can determine the quality of a filter by looking at the minimum efficiency reporting value, or MERV, and the dimensions on the long side of the filter.

  • MERV 1-4 (decent): These filters can pick up particles like pollen and regular standing dust, about 10 microns or larger.
  • MERV 5-8 (good): These filters are better at catching small particles such as mold spores, hair spray, dust mites and animal dander, typically 3-10 microns in size.
  • MERV 8+ (better): These air filters can remove very small pollutants including particles like humidifier dust, auto emissions and legionella, which are 1–3 microns.

Ultimately, you’re better off spending a little extra on a quality filter that has some staying power.

Other Factors

In addition to the previously mentioned factors, there are a few other things that can influence how often you should change a furnace filter. You can expect your filter to clog up faster if you have lots of guests or several people living in your home. If you smoke, leave your thermostat at “on” instead of “auto” or tend to leave your doors and windows open, your filter won’t last as long. You should also consider changing out your filter more frequently during the peak winter months between December and February.

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