New filter vs. used filter

Home Air Filter Replacement

Whether it is an air conditioner, furnace, or heat pump, if it moves air – it has an air filter. Replacing the home air filter is perhaps one of the most important maintenance routines you will do. Air filters come in different sizes, styles, and qualities. By the end of this article you should be well equipped to choosing the right air filter for your home, as well as having the ability to do it yourself.

Why Air Filters are Important

The easiest answer to why air filters are important is found in their name – they filter the air. There are many things floating around in the air that we cannot see, and some that we can, such as pollen, mold spores, pet dander, etc. Depending on the season or which region you live in, these could potentially be at undesireable levels. Air filters are designed to remove as many of these particles as possible, thereby offering a cleaner environment within your home.

Air filters serve another purpose as well, preventing the buildup of lint, dust, and other contaminates from inside the air ducts in your home. Many issues, health or mechanical-wise, can be introduced if this buildup becomes excessive. For health reasons because they will filter the “undesirable” particles from the air in your home. For mechanical reasons, the dust and lint can cause build up on the blower and inside the ducts which can restrict the airflow making your furnace or air handler work harder to push the air, and end up causing potentially very expensive repairs to be made, which could literally range up into the thousands of dollars!

Take a look at the difference between a new filter and one that has only been in for a couple months. This is a great example of how effective the air filter really is!

New filter vs. used filter

How Often to Change the Filter

Air filters can normally be found with change frequency ratings, the most common one being one month. How often one actually needs to change the air filter is dependent on several factors. Are there pets in the home such as dogs and/or cats? Do you live in a dusty or region with high levels of mold spores? If you answered yes to either of these, then you may want to change the filter more often than the manufacturer’s recommended frequency. Example, if you live in a hot and humid environment, you may want to change a 1 month filter about every 4 weeks rather than the full 30-31 days of each month. If you have several cats or shedding dogs, a 3-4 week schedule may be more in line. A good rule of thumb is to not change it longer than the manufacturer’s recommended frequency.

Types of Air Filters

As there are many different types of filters, there are only a few important attributes you need to worry about – size and quality. The first would be the size. This can easily be found on the filter itself, by removing it from the filter compartment. The size will be denoted as dimensions, such as 16″ x 25″ x 1″. The next attribute would be quality, as gauged by the MERV rating. MERV stands for Minimum Efficiency Reporting Value, which simply put means how many of the particles and contaminates it will filter out of the air. MERV ratings are on a scale from 1 to 16, 16 removing the most out of the air. Some manufacturers don’t use the MERV scale, rather they use their own, so look for a scale graphic or similar visual rating to see how their product actually compares.

Air filter quality ratingPictured here is a rating system used by The Home Depot on the air filters they sell. The brands you will find there are Rheem and Honeywell, both of which are established and high quality brands.


How to Change the Air Filter

Air filter compartment example   Air filter removal

The first thing to know in changing the air filter is to know where it is located. If your furnace or air handler is in a closet or attic, then it can be found in a small compartment between the return duct and the furnace itself. In some cases, you may find the filter either in a large return air grill located inside the home. These compartments are easy to open, normally only requiring at most to loosen a couple latches. This will allow you to remove the old filter and replace it with a new one.


Direction of air flowPay attention to the way the filter goes in. You will see an arrow graphic on the thin edge of the filter which tells you the direction of air flow. If the filter is located in a grill, point the arrow toward the inside of the duct, away from the room. If the filter is in a compartment between the return duct and the furnace, then point the arrow toward the furnace.

Let’s Do It!

Now that you have the why, where and how, it’s time to do! Replacing your air filter is one of the easiest yet most important maintenance tasks you will do around the home. If you have any questions or have any input, feel free to comment below. Thanks and good luck!





5 Comments Posted

  1. This is one of the things that I struggle with. I always forget to replace my filter. I have to be reminded to change my car filter haha :). I like that you provided this information to knowledge people on how important it is. I mean this can effect your health as well I’m sure.

  2. This is some useful information for all. Often I will forget about the filter until I sense something is wrong with the furnace. I understand now how being pro-active is advantageous bodes well as a preventive measure

  3. I actually have a dog and live in a hot climate. I think I should change an air filter once in two-three weeks. Is it a good frequency?

    • If you use the lower quality filters, I would suggest a 3 week change frequency. If you look at some of the higher quality filters (normally twice as expensive), they will show you they are designed for pets. If this is the case, you can use the frequency they suggest. Some actually are up to 3 months, which may be worth the extra money.


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