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How to replace your AC filter

Posted by AMH Team

4m read time

Aug 16, 2022

Home air filters do two important things. First, they clean the air and make it safer to breathe. Secondly, they protect your home’s HVAC from small particles, which extends its life and reduces the amount of energy it needs to operate.


To ensure your HVAC system operates at peak efficiency, you’ll want to make sure you get it inspected and tuned up at least once a year. While a tune-up can be complicated and should only be performed by a trained technician, there is one thing you can do as the resident that’s just as important and far easier: regularly replace your home’s air filters.


Read on for our complete guide to help make this a simple routine step that seamlessly fits into your annual maintenance checklist


Why is it necessary to change an air filter?

Changing your home’s air filters ensures the air you breathe will continue to be clean and safe, and it will make it easier for your HVAC system to run. A clogged air filter puts an unnecessary amount of strain on your HVAC system, which can reduce its efficiency and increase your home’s energy costs. Plus, homes with poor air circulation are more likely to have harmful pollutants floating in the air. Even if you don’t have any allergies or breathing issues, your home’s air filter is vital to both your short- and long-term health.  

How often should you change your air filter?

It depends on how thick your air filter is. Typically, one-inch air filters should be replaced every one to two months, while two-inch filters don’t need to be changed until every three months. Three-inch filters should be changed every four months, and four-inch filters should be changed every six months. Read on to learn how to measure your filter, although the manufacturer should also have recommendations printed on the packaging detailing how often you should replace your air filter. 

Measure before buying

Air filters come in a variety of sizes, and you’ll need to pick one with the right dimensions to ensure your home’s air is adequately filtered. To measure, first locate your home’s air return duct. Most homes have a large square or rectangular grill covering the duct, and it’s usually on either a wall or ceiling in the center of the home. If you have a multi-storied home, you probably have an air return duct on each floor. 


If you’re unsure whether you’ve located the air return duct, there is a simple test you can do to verify you’re in the right place. With the HVAC system running, place a small piece of fabric over the grill. If it is pulled into the grill, you’ve located an air return duct. If instead it is blown away, you need to keep looking.


Once you’ve located the air return duct, you’ll need to remove the grill covering the opening. Once it’s open, measure: the distance from left to right, the distance up and down, and the thickness from front to back (note: you are only measuring the distance from the grill cover to the metal rim that houses the air filter, which is commonly one inch).


These three measurements combined will determine what size air filter to buy for your air return vent. Common sizes are: 20x20x1, 16x25x1, 24x30x1, and 20x25x2. If you get a measurement that is a fraction of an inch above a whole number, round up to the next whole number, e.g., round 19.75 inches up to 20 inches.

How to change an air filter

Follow these steps for changing the air filter at home:


Turn off your home’s HVAC at the thermostat.

Doing this will prevent air from pulling the old air filter into place and prevent any dust and particles from flowing into your HVAC system.


Open the grill.

Some vents need to be unscrewed from the wall, while others have metal tabs that push aside, allowing the grill to pivot open. 


Remove the old air filter.

If you have any allergies, you may want to wear a face mask and disposable gloves. The air filter may be very dirty. If it is, place the old air filter in a large trash bag and promptly remove it from your home.


Place the new filter into position.

For correct placement, the filter may have arrows that illustrate the direction of the air flow. If the filter is not placed correctly, your HVAC may have to work harder to pull air, which will drive up your energy bill and reduce the quality of your home’s air. 


Close your grill.


Turn on your HVAC.


Pro-tip: If the grill covering your air filter is dirty, it will decrease your filter’s useful life and make it more difficult for your HVAC system to circulate air. Therefore, you can extend your air filter and HVAC’s life by cleaning the grill before powering on your HVAC. This is easily done with either a vacuum or moistened paper towel. 

Bottom line

Change your air filter as often as the manufacturer recommends to improve your home’s air quality and increase your HVAC’s efficiency. After you determine how often you should be replacing it, we recommend marking your calendar so you don’t forget. Last but not least, if the AC unit is elevated off the floor, please ensure your safety by using a stable stepstool to reach it!  

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