When Should I Change My Air Conditioner's Air Filter at Home?

February 26, 2015

Every once in a while we’re asked what is the number one thing that Denver area homeowner's can do to secure their air conditioning and heating system between their scheduled tune-ups? The answer is simple this; remember to change the heating and air conditioning air filter. Replacing furnace and return air filters is extremely important to the effectiveness of your HVAC system, not to mention your home's air quality. Did you know indoor air pollution is one of the top five environmental health risks? We know it's the last thing on your mind, but this is really important stuff. Changing the air filters is not a tough thing to do for most Denver homeowners, but there are usually two hurdles to actually completing this job:

  1. Understanding just how often to swap out your furnace or air conditioner filter.
  2. Remembering to change air filters when needed.

When To Change Your Air Filters

Most filters have a printed "expiration" date on the box or plastic. It may say "Lasts up to 3 months" or "Change filter every 90 days". Look around at the store and you should see that some are designed to only last a month, while other manufacturers (like Honeywell) have released media air cleaners with filters meant to be swapped once every 6-12 months. The standard seems to be once every 3 months for most higher quality filters, but we have a rule of thumb that we recommend our readers to go by. If they're dirty, change them! A dirty air filter can add or cause damage to costly components, like your compressor, so it's better to change it out more often than neglect it. If you want to follow the manufacturer's recommended limit, we suggest writing the date on the filter when you swap it out, and adding a reminder for yourself in your phone or on a calendar. Keep in mind that your filter manufacturer may have a different recommendation from your HVAC system manufacturer.


  • Which air filter your system requires
  • The entire air quality of your Denver area home
  • Pets – Cats, dogs, birds, etc.
  • Occupancy of the home
  • General air pollution in the Denver area or construction taking place nearby

For your typical 1"-3" air filters, the manufacturers basically suggest to change them bi-monthly, which is really a great rule of thumb. Still, general rules aren't always for everybody. If you have to endure light to moderate allergies, you might need to upgrade your air filter or change them even more frequently than OEM specifications. On the other hand, if you're in a remote area, own a less occupied home (like a vacation home) or an area with little auto traffic, replacing your air filters each year may be quite sufficient. Why do we call out our beloved pets? They have a tendency to shed, which can clog your air filter quick. Of course, the air filter is just doing its job by capturing pet hair and dander, but tremendously dirty filters can cause seriously reduced HVAC performance.

In summary:

  • Typical suburban home without pets: Change every 90 days
  • Got a cat or dog: Change every 60 days

How To Remember To Change Your Air Conditioner's Air Filters


How to replace your return air filter

Most of you know how to replace the air filter in their system, but some houses have an extra filter in the return vent. Whether you have one or not is dependent on the HVAC manufacturer's recommendation. Your HVAC is engineered to handle a set amount of pressure in your home sweet home, and the more filters you have the fiercer the blower motor works, which can reduce the lifespan of your system if it isn't designed for it. Finding out whether you have a return filter and replacing it is easy:

  1. Go to your return air vents.
  3. Look for a filter. If one is there, pull it out and write down the size.
Crazy as it may seem, filters can dramatically affect your home's airflow, which is why we recommend checking in with the manufacturer. A more expensive HEPA filter that is designed to catch finer particles will restrict airflow more than a cheaper filter. With restricted airflow comes increased pressure on your system, so you need to verify that your HVAC system was made to handle it. Otherwise, you could experience lowered heating and cooling efficiency in your home, and system parts may break down much faster than normal.
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