How to Choose An Air Filter for Your Central Air Conditioning Unit

ByMarc Silberberg


Welcome to the wonderful world of central air conditioning. You may be a new homeowner who is experiencing the luxury of central air for the first time or a happy one who has upgraded and installed central air into your home recently. There is nothing as comfortable as this type of cooling system that requires little maintenance by the homeowner other than checking and changing your air filters frequently. If you are a seasoned central air user, then you know that yearly maintenance by a professional is essential to keep your central air at its highest efficiency.

New members to the central AC club may not have been told by their rushed installer that their system has filters that must be always kept clean. You can avoid having to call your air conditioning specialist when your AC is running but not cooling the house the same way it did when it was newly installed. Chances are if your HVAC system is new that the problem will be with the filters. Some folks do not even realize that there are filters in their HVAC system, nor do they know where the filter exchanges are in their homes.

When your HVAC system becomes clogged with debris, dirt, and other foreign residues the efficiency of the system decreases causing your electricity bill to increase while still not cooling properly. When the filters are dirty the blower must work harder which can cause internal damage in your new units. The area that you live in and the type of units you have will determine how often you need to change your filters. Monthly checks of your filters will give you an idea how often to change them but at least every three months or less. Outdoor pollen counts will expose your filters and you may have to change them more frequently.

Not only is it important to change your filters as needed but the type and size of the filters must be right for your system as well. The wrong size filter can cause your system to work inefficiently and become overworked so always check the old label of your present filter to see the right size and model. If your old filter doesn’t have any identification on it be sure to measure it correctly before purchasing a new filter. It is tempting to buy a box full of filters as this is usually more economical, however, we caution new owners to try to buy as little as possible making sure they check the make and model of their AC unit before purchase. It certainly would pay to ask your AC installer for as many extra filters as possible even if you must pay for them; in fact, many maintenance professionals will not bring along new filters when checking your machines unless asked specifically to bring them along.

How Do You Know Which Filters to Buy?

Other than size there are several other variables that must be explored both from monetary and efficiency costs. Before buying any filters in bulk try different models and determine which ones work the best for your HVAC system to entrap pollen, dust, dander, and various allergens keeping the air of your home as clean as possible. One might believe that pollen is only outdoors but actually the concentration of pollen indoors is much higher proportionally. Winds and rain will blow and wash away outdoor pollen but indoors the pollen tends to remain stagnant.

Filters come in different sizes and thickness and which one you choose depends entirely on your system. Air filters that are thicker have two main advantages, the filters are finer and require replacement less frequently. Central Air filters are usually made from pleated materials and fiberglass. Thinner and less expensive one-inch filters are generally found in the older systems so not every HVAC system can take a thicker filter. Personally, we tried thicker filters in our own older HVAC system and the system worked less efficiently and finding those old thinner filters is not easy. Some older systems can be refitted to accept the thicker filters by upgrading the ductwork.

There is a grading system by manufacturers for filters which is called the MERV (minimum efficiency reporting value) for each type of filter. This system was first developed by ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers). Other companies such as Home Depot and 3M have their own grading systems named MPR (microparticle performance rating) and FPR (filter performance rating).

Here is a sampling of the ratings of Consumer Reports of some popular AC filters currently on the market:

1 – Filtrete 2500 Smart Premium Allergen Ultra Fine Particles S-EAX22DC-6

For those of us who are forgetful when it comes to air filters for our HVAC systems these higher priced filters are the choice. These filters have an Excellent consumer reports rating for their effectiveness in removing airborne particles while the system runs on the highest fan speed, when the fan is on the lowest speed the particle removal is only moderate.

What makes these filters desirable is their “smart technology” which means you can look at your smart phone app and check the condition of your filters to see if they need to be replaced. The manufacturer advises that the filters should be replaced about four times a year which will cost the homeowner $100 depending how many filters are needed. You may not be impressed with this smartphone technology since you may just need to put a reminder on your phone. Also, one never knows how their AC will act and filters may have to be replaced more or less often than indicated by the app.

2 – Filtrete Ultra Allergen Reduction 1500 MPR

Consumer reports gives this less expensive filter a Very Good rating for the removal of dust, pollen, and smoke when the system is working on high fan speed but only moderate when on the lowest fan speed. At both speeds the airflow through the filter is strong and this company recommends four times a year filter changing at the cost of $86 annually.

3 – Carrier 5-inch thick EZ Flex

This filter has a consumer reports rating of Very Good with a MERV rating of 10 when running on the highest fan speed. However, when running on the lowest fan speed the rating drops to Good but it still will maintain good airflow at either fan speed. This company advises the consumer to replace the filter twice a year at the cost of $128 annually.

4 – Filtrete Healthy Living four-inch- thick Ultra Allergen 4 MPR1550

This air filter earns the Very Good consumer reports rating on both highest and lowest fan speeds. The air flow is great and unrestricted at either speed costing about $29 per filter with advice to replace only once a year making this the most economical of all the filters tested by consumer reports.

5 – AprilAire Healthy Home 213 MERV 13

This four-inch-thick filter has a consumer reports Excellent rating when the HVAC system is working at the highest fan speed and does almost as well on its lowest fan speed with an annual cost of $41 since AprilAire only recommends replacing the filter once.

Where Are Your AC Filters Located? 

There are filter locations inside and outside most homes and different units will have somewhat different places. Outside filters will be located near the return vent which looks slightly larger than the air vents. To find the return vent, take a paper and put it near the vent while it is on, the return vent will pull the paper toward it.

Most indoor units have at least two filters. Look for a slot close to the air handler which is the box that holds the unit parts which is usually in the attic or basement. (My filters are changed from my second-floor ceiling).

Final Words

Now that we are apprised of the important fact of HVAC filter replacement it is up to each individual homeowner to assess the situation with their own HVAC systems. There are several variables that will determine how often the filters need to be replaced, namely, the age of the system, the environment, pollution, and outside pollen. As we learned from the different descriptions of the filters, when the system’s fan is kept on low the filters will not work as efficiently as when the fan is turned to high. As we learned from the different descriptions of the filters, when the system’s fan is kept on low the filters will not work as efficiently as when the fan is turned to high. So, although on the one hand, the homeowner will want to save electricity by keeping the fan on low the filtering out of allergens, pollen and other dirt will be decreased.

As we learned there is no one set answer for any homeowner’s maintenance of their HVAC system. As long as there is a professional who comes in before the system is turned on the chances are excellent for a stress-free summer. Remember to ask your AC specialist which filters he recommends and to ask him to install them for you. This will assure that your filters will be put in the right way and not upside down. Each HVAC system takes different width filters, and some may not be able to have the thicker ones fitted. Don’t get confused by all the different types of AC filters, you will get to know which ones will fit and be the best for your system.

All Blog Articles

Get Free Estimate

Give us some info and we'll get right back to you with a quote


    How can we help?


    At NJ AIR QUALITY, we get excited every time the phone rings or another contact form is filled out. That’s because we LOVE what we do. And we look forward to doing it for YOU!