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Air Conditioning Filters 101: What You Need to Know

Air Conditioning Filters 101: What You Need to Know


Seems like a simple topic, but it can be confusing at first. Most consumers don't know enough about them to make informed decisions.

An air conditioning filter is an essential part of your HVAC system as they keep the air in your home clean and breathable. If you’re in the market for a new filter, there are a few things you should consider before making your purchase. Keep reading to learn what you need to know!

Where is my filter located?

For any homeowner, or anyone living in a place where you have an AC unit, it’s important to know where your filters are located. Depending on which type of unit you have, you will find your filters either on top, below, or on the side of your unit. In some cases, your filters will be located behind the return air grilles in your wall, ceiling, and in your utility closet.

So, how do you know which kind of filter you have and where they’re located? The first step is figuring out which type of HVAC unit you have.

Window Unit:

If you have a unit that is located in your window, you’ll find the filter where the air comes into the unit.

Note: the filters for these units are reusable. You are able to clean them by vacuuming, washing, or rinsing from back to front.

Mini Split Unit:

If you have a mini split unit, where you have an indoor and outdoor handler, the filter will be located in the indoor unit. This can either be on your wall, ceiling, or ducted/concealed. 

Note: the filters for these units are reusable. You are able to clean them by vacuuming, washing, or rinsing from back to front.

Central System:

If you have a central system, also known as a ducted or unitary split, you’ll find the filter on the side of the air handler unit. This unit will be located in your basement, in a closet, or on your ceiling.

Note: the filters for these units cannot be cleaned and must be replaced every few months depending on which type of filter you have.

Packaged Unit:

If you have a packaged unit where the condenser and air handler are in one unit on the outside of your home, the filter will be located either on the side, indoors where return air leaves your home and goes back into the machine, or on the outside of the machine. 

Note: the filters for these units cannot be cleaned and must be replaced every few months depending on which type of filter you have.

Knowing where your filters are located means knowing exactly when you’ll need to change them. If you have a window HVAC unit, for example, and the filter is in the slot on the air return, it’s easy to see when your filter is starting to get dirty. You may even notice that it causes issues with your air flow. If you have a vertical unit and the filter is above or below it, you may notice that water has begun to collect on top of the unit.

However, if you have a unit that has the filters behind the return grille or in your utility closet, you obviously won’t be able to see when to change them. This may even lead to using more energy in order for your AC unit to maintain its efficiency.

What is a MERV Rating?

Believe it or not, air conditioning filters are actually rated on how well they can filter your air. This is called their Minimum Efficiency Reporting Values (MERV) rating and goes according to EPA standards. The higher the rating, the more filtration you’ll get. The EPA generally recommends a minimum of an 8 for the average home, but if you have allergies or other specific health needs, it’s best to go higher than that.

What are the different MERV ratings on air filters? Here’s a breakdown of the most common grades:

MERV 1 through 4 – These are barely effective in removing allergens from your home and should be avoided. They’re not very efficient and can only catch larger particles like pollen, sanding dust, and dust mites.

MERV 5 through 8 – These grades are considered the “standard” of air filtration and trap around 92% of particulates in your home. They catch large amounts of pollen, dust mites, pet hair and dander, mold spores, and other indoor pollutants.

MERV 9 through 12 – These are considered “high-efficiency” filters and remove around 95% of the particles in your home, including bacteria, mold spores, and pet dander. They’re best for households with people who suffer from allergies or asthma.

MERV 13 through 16 – These high-end filters remove virtually all contaminants from air through a process called Ultra-High Efficiency Filtration (UHEF). They remove 99% or more of airborne bacteria and viruses, making the home environment safer for those with immune deficiencies and respiratory problems.

MERV 17 through 20 - At these levels of filtration, 99.97% of impurities are forced out of the air. They’re even used for those with major health problems like cancer patients and people undergoing chemotherapy because they remove any traces of bacteria or viruses from the air. These filters are not used in commercial settings or sold to the general public as they are only typically used in settings like hospitals, scientific labs, and manufacturing facilities.

Make sure you choose a high MERV rating filter (like those that are 5 or higher) in order to get the best quality air! You certainly wouldn’t want to block too much airflow. You will be able to see which rating any filter has when you buy it, so be sure to look for the numbers starting with a 5 or higher.

How often should you change and clean your filters?

As a rule of thumb, your filter should be changed at least every 90 days. If you change the filter more frequently, you’ll have healthier air and save on electricity—and frequent filter changes are better for the environment. However, depending on which type of filter you have, you may need to change them more frequently. For more information on the different types of filters and how frequently you should change them, read our blog: Air Conditioning Filters 101: What You Need to Know.

If you’re someone who is looking for a long-term solution and you don’t want to be bothered with changing your filters every few months, a washable filter may be perfect for you. These kinds of filters will last you at least 5 to 10 years and all you need to do is wash it out in your sink every 90 days. Not to mention, you’ll save lots of money!

To wash your washable filter, all you have to do is remove it from the unit and empty out all of the collected debris. Then, use a water hose to spray down your filter. You should also periodically vacuum out the inlet on the backside of your system for better airflow and efficiency.

1. What you need: A water hose, cleaning solution, and filter vacuum cleaner attachment or a sponge.

2. How often: As frequently as needed (depends on the size of your system) or every 90 days.

A dirty filter can lead to a multitude of problems in your household. For starters, it can cause strain on your unit and make it work harder than it should. This leads to higher energy bills as well as unhealthy air and reduced airflow, which may result in an uncomfortable home environment for you and your family.

Striking the right balance between filtration and airflow

Choosing the right air filter for your home or business is important because a good filter will protect you from dust and other allergens. It will also help deliver clean air to your HVAC system, which in turn can improve energy efficiency. There are many different types of filters on the market, so it’s important to know what to look for.

Here are our top 3 most important things to consider:


Thicker materials are designed to last longer and can trap small particles that tend to get through thinner filters. However, if you have a very small HVAC system, such as in a home office or closet, buying and installing a thick filter may not be the best option. The added thickness of the filter can reduce airflow to your HVAC system too much — especially if it’s already small.


The frame of the filter should be made from sturdy materials. It will support the filter and hold it in place while keeping it off your HVAC system’s internal components, including the blower wheel, which can be damaged by particulates. A sturdy frame is also necessary for cleaning the filter.

If the filter does not have a frame, it will likely use mesh or some type of webbing to hold it in place inside your HVAC system. The webbing should be made from fibers that are strong enough to support the weight of the filter and resist damaging the blower wheel.


The rating of the filter will tell you how much particulate matter it can remove from your home or business. As discussed earlier, filters with a MERV (minimum efficiency reporting value) higher than 8 are the most effective at removing particles. If possible, choose a filter that can effectively capture allergens like pollen, dust mites, and pet dander from the air in your home.

Some filters are designed to filter out specific types of particles. For example, a carbon filter can help remove odors from the air and is typically used for odor removal, while a HEPA (high-efficiency particulate air) filter is ideal for removing allergens from the air and also has antibacterial properties that may help reduce or eliminate mold and bacteria in your HVAC system.

The right type of filter will depend on what you’re trying to achieve.

If you want your HVAC system to be more energy-efficient, look for a filter with a high MERV rating and clean it regularly. If you are trying to remove allergens from the air, choose a HEPA filter made from strong fibers that can hold up over time.

Remember, as a general rule of thumb, we recommend the perfect balance of a MERV 8 filter. If it’s been a while since you’ve purchased an air conditioning filter, we can help by giving you advice on which type would work best with your system and needs. And when you’re ready to make your purchase, HVAC Premium has a wide range of filters and will have what you need!

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