Why Does Central Air Have Two Filters: Do You Need Them Both

If you are a first-time homeowner or just installed central air, it may surprise you to learn that there are two filters. Each of these lives up to its name by filtering out undesirable dust and debris to keep it from getting inside your vent system and your lungs. Since central air pulls from the outside and has indoor vents, there are necessarily more filters. If you have an especially large central air system, you may even have more than two filters. While both types of filters serve similar purposes, it’s important to understand that they don’t necessarily have the same working lifespan. Always check the directions to make sure you replace filters on time. Doing so will help keep your indoor air clean and healthy and avoid buildup in your vents. 

Why does central air have two filters? Central air has two (or more) filters because it’s important to clean both the air headed into the handler and the return filters that go into the system. Some homes, especially multi-level houses, can have several air filters, but they fulfill the same purpose as having two. Each air intake needs to remove dust and debris. Filters accomplish this and keep your central air clean and functional. 

Where Are the Two Filters in My Central Air

The exact location of air filters in central air varies, and you may have one, two, or more. I will walk you through finding the relevant filters to replace them as necessary. The air handler vent should be beside or near the unit itself. Meanwhile, return vents are in various locations around a home, but they’re usually easy to locate due to their appearance. 

Return Vents

Return vents are typically characterized by a white metal grate with screws or toggles to release it. Large homes and multi-story buildings may have multiple units or return vents. Since smaller homes have a single return filter and most homes are smaller, most people have one filter to change. For this article, that counts as ‘one’ type of filter even if you have more. 

The screw openings require a flat-head screwdriver or even a small coin to open, and the newer style flips open with the pressure of a thumb. Inside you will find a rectangular filter with a cardboard border. The inside is a wire mesh over an accordion-folded filter to catch dust, pet hair, and other dirt. These filters sit in place with just the screen and some air pressure from the suction, and the metal mesh should always be facing away from you on installation, so you don’t see it. 

You will usually find the return vents in the wall, but they may be located on a floor or even a ceiling. An easy way to check to see if it’s a return vent is to turn on the system and see if a small piece of paper sticks. When it does, that is pulling air through to return it to the central air system. This prevents unnecessary pressure buildup in the home and allows air to move. 

The ingenious Filtrete S-UR22-2PK-6E Smart Replenishable AC Furnace Air Filters fit many return filters, though you should always double-check the measurements first. These are the first Bluetooth enabled ‘smart’ filters that self-track and notify you when it’s time for a change based on airflow. The app to monitor your filters is available for both IoS and Android systems and includes information on the size and type of filter you need for easy reordering. See the amazing Amazon reviews when you click here. 

Another easy way to spot your vent covers is dust. The front of the vents will collect a fine layer of debris over time from pulling air in. It’s a good idea to wipe this off when you change the filter, or more often as needed just for basic sanitation. 


The filter on an HVAC is usually directly beside the air handler. According to Second Nature, “The air handler is the large metal box containing the fan and fan motor. Typically, the unit would be found in a basement, an attic, or sometimes in the back of a closet. ” Once you’ve located your air handler, the filter is easy to find since it has a one or four-inch thick hinged opening. 

Inside this opening, you will nearly always find a filter already in place. Don’t be too surprised if this filter is incredibly dirty since many homeowners forget or never knew they were there in the first place. These filters are similar to the return vent style, but they are often square or cube-shaped. 

The AF MERV 8 Pleated AC/Furnace Air Filter Packs from Amazon are a hundred percent manufactured in the USA. Moreover, they filter out ninety-percent of all airborne particles, and they last up to three months’ apiece. Plus, they are humidity and high temperature resistant. Learn more by clicking here. 

Swapping out a filter is incredibly straightforward. Pull out the old filter, wipe any dust away with a damp cloth, and replace the new filter when the area is dry. No special disposal methods are needed either since you can up the cardboard and cotton filters into a standard trashcan. 

Installing Central Air Filters Correctly

A central air filter, or two, is not a complex piece of machinery by itself. The sturdy cardboard frame holds cotton or synthetic sheets of accordion-folded fabric and some basic wire mesh. Science and testing go into creating these simple ‘crud blockers,’ you do not need special skills, tools, or knowledge to replace them. 

The packaging on your filters will give the best overall estimate on how frequently you should change them out. Make sure to mark the date of your next change down on your calendar just as you would for any other basic home maintenance task. That said, you should only consider those timeframes as the maximum possible working life for each filter. 

If you do not occupy a home for several months or only live there part-time, then the weeks or months you are not using any air don’t count toward the filter’s usage. Naturally, a home that has been dormant for a year or more should get clean filters. Moisture and other contaminants can still settle inside an unused system. When in doubt, switch them out. 

As for the physical switch, you may be surprised at how straightforward it is. Unless something truly unusual has occurred, you open the cover, pul a filter out, and put the new one in its place. I also recommend wiping any excess dust off of the area, but that step is optional. Some filters use tape or velcro to hold in place, but many don’t even need this basic addition.

If you want a smart alternative to standard filters, an HVAC/Air Filter Media Roll from Amazon can be cut to fit any size. Commonly used in HVAC – R, these orange polyester antimicrobial rolls provide a longer-lasting solution that you can use to replace filters over time and outstanding mold prevention. Have a roll delivered to your door by clicking here

Should All Air Returns Have Filters

Whether you choose to put two filters in your central air is up to you; however, systems designed for multiple filters should have them in place. Your air filters help remove dust, dander, allergens, hair, and more from your home. Additionally, they help keep that debris out of your vents. 

While the intakes for your central air also help filter out contaminants to provide clean air, the filters offer extra removal. With less mess, your system will usually need less cleaning, and blockages are also more infrequent. A heat pump system without filters can result in buildup on the evaporator coils leading to condensation and clogs. In short, you can take out the filters, but doing so is likely to cause several problems in the long run that are easily avoided. Plus, you will quite literally breathe easier. 

Internet speculation that these filters cause your system to overtax its fans is largely based on misinformation. If you’re not certain, always consult a professional for answers. 

Final Thoughts

There’s no reason to breathe dirty, unfiltered air. By switching out both of your filters on a regular schedule, you can help prevent allergies and reduce the chances of damaging buildup inside your central air system. However, it is important to pay attention to any instructions and make timely filter changes. 

If you have more people, pets, or mess than most homes, you will need to change your filters more often. Regardless of the estimated working life of a filter, you should check every two weeks until you’re sure how long it takes your home to dirty a filter. It’s normal for these filters to change color as they accumulate dust, hair, and other contaminants. When your filter is full, it’s time for a change. 

Although some people argue that you don’t ‘really’ need all the filters as long as you have one, it’s best to go with the information provided by your system’s manufacturer. Keeping the air clean and at a comfortable temperature is a complex job that your central air’s designers and installers know better than anyone else. 

Aron Blake

I am the lead copywriter on Homezesty and the Webmaster. I have a lot of experience in home renovations and the creation of style. I enjoy writing and sharing my tips on how to create the best living environment. My Linkedin Profile, My Twitter Account

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