What Is an Air Conditioning Filter?

An air conditioning filter is a screen that fits into the return air duct of an HVAC system to filter out dirt and debris while still allowing clean air to move through it. These filters are essential for clean home air because humans and pets can create a lot of unhealthy airborne particles. Air conditioning filters trap particles like smoke, pollen, dust, pet hair, and dirt, letting fresh, cool air move through and into your home.

With so many different types of air conditioning filters, learning the differences is essential for finding the right air filter for the HVAC system in your home. Read on to learn more about air filters, how they work, and which one is best for you.

How Does an Air Filter Work?

Air conditioning filters use materials like fibers or pleated fabric. Some of them rely on mechanical filtration, where particles get physically trapped in the material. Others use static electricity or activated carbon to attract and capture small particles and odors. 

As a filter captures more particles, it can start to clog over time and limit how much air can pass through. Some filters are washable to be more eco-friendly, but many still have a fixed lifespan. If that’s the case, you’ll need to remove and replace the filter on a regular schedule.

For more on how air filters work, check out this video from one of our top brand picks.

What Are the Most Common Types of Air Conditioning Filters?

Just as there are multiple types of air conditioners, there are also lots of different filters on the market. Your goal is to find a filter compatible with your own HVAC system. Here are a few of the most common options.

HEPA Filters

High efficiency particulate air (HEPA) filters are considered the gold standard for their high efficacy. They can’t handle most gases and odors, but according to the United States Environmental Protection Agency, they filter out about 99.97% of these airborne particles, including dust, pollen, bacteria, mold, and other particles .3 microns or larger.

Before you purchase a HEPA filter, check to see if your air conditioner will support it. Because they’re so dense, they can restrict airflow in some systems. Check out our guide to HEPA filters for more information.

UV Light Filters

Ultraviolet (UV) light obviously won’t work to filter solid contaminants like dust. However, it’s effective at killing mold spores and bacteria. In combination with other filters, a UV filter can be valuable if you live in humid climates or are concerned about microbial growth. 

One drawback of these filters is that they can transform oxygen into ozone, which can be hazardous to your health in high concentrations. If you’re unsure whether a UV filter is worth it for you, consider the other options in this list first.

Spun Glass Filters

Filters that use layered fiberglass are some of the most affordable you can buy, and since they allow more airflow, they won’t strain your air conditioner as much as a denser material. However, they aren’t a reliable option for trapping small particles, so if you have allergies or live in an area with lower air quality, you may want to consider other types of filters.

Pleated Filters

Pleated filters are made from cotton folds or polyester. They offer a larger surface area for trapping small particles and a longer lifespan than fiberglass. You may consider them if you don’t have allergy issues or want a good balance between quality and cost.

What To Know About Filter Rating

The industry standard for measuring a filter’s efficiency is the Minimum Efficiency Reporting Value (MERV) rating. Each AC filter receives a rating between one and 20, with higher-rated models capable of trapping smaller and smaller particles.

Most residential HVAC filters have MERV ratings between one and 12. A 12 rating can capture particles between 1 and 3 microns in size. However, they also have high airflow resistance, which could strain some air conditioners. Consider your system’s capabilities, and ask your HVAC contractor if you need help finding the perfect sweet spot for your individual needs.

DIY Filter Replacement Tips

Replacing an air conditioning filter is a simple DIY task that most homeowners can easily manage. Here are some tips to ensure you complete a successful DIY filter change:

• Locate the filter: With most HVAC systems, the filter is where air returns to the unit, so clean air circulates through most of the network. This is usually in the return air duct or the air handler unit. If you don’t know where the location is, check the system’s manual.
• Check the size: The replacement filter should be the right size for your HVAC system. Before you go shopping for a new filter, check the old filter frame for printed dimensions.
• Note the airflow direction: Most filters have arrows printed on the frame that indicate the correct airflow direction. Install the new filter with the arrows pointing toward the HVAC unit.
• Dispose of the old filter: Handle the old filter carefully and place it in a garbage bag so trapped particles and allergens don’t go airborne. 
• Mark the replacement date: Write the installation date on the new filter’s frame to keep track of when you should replace it. That way, you can keep track of the filter’s lifespan and start a consistent replacement schedule.

Final Thoughts on Air Conditioning Filters

While there are plenty of different types of air conditioning filters to choose from, there isn’t just one right or wrong pick. As long as you’re filtering the air that’s moving through your air conditioner, you’re doing your part to create a cleaner, healthier home with better indoor air quality.

If you’re unsure what filter to buy, call an HVAC company so you can work with an HVAC pro to find the filter that suits you best. Also, consider getting regular HVAC maintenance and filter replacements to extend the lifespan of your AC system. Check out our guide on how much HVAC maintenance costs for a better idea of what to expect when you hire a professional HVAC company.