7 Myths About HVAC Air Filters Debunked

replacing filter in central hvac system

There are plenty of myths surrounding air filters, some of which can actually harm your air conditioning system. For example, a common myth is that you should always get the strongest air filter you can find, but this can restrict the airflow in your ductworks. Thankfully, these kinds of myths can be easily disproven. Read below for 7 myths about HVAC air filters debunked.

What Are HVAC Air Filters?

The air filter in your HVAC, also called the AC filter or furnace filter, is a very important part. It catches particles moving through the air entering your duct system so that they don’t cause problems for your air conditioning unit. Dust, mold spores, and allergens like pet dander can all seriously damage your AC if you don’t have an air filter. Not only that, but you’ll end up breathing in more contaminants that can cause breathing issues.

What Is MERV?

Every air filter has a MERV rating. MERV stands for Minimum Efficiency Reporting Value, and is a scale used to measure a filter’s effectiveness. It ranges from 1 to 20; 1 is the least effective and 20 is the most, though the majority of filters don’t go above 16. Filters that are higher up on the scale can trap smaller particles, as well as higher percentages of particles overall.

Myths About Air Filters

Myth 1: All Air Filters Are The Same

Senior Man Changing a Dirty Air Filter in a HVAC Furnace
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One harmful myth is that every air filter is the same, so it doesn’t matter which one you pick. This is untrue, as there are a wide variety of filter types available, each with their own MERV ratings and pros and cons. Here are the different kinds of filters and a short description of each:

  • Pleated Filters: Filters made from a medium of pleated paper, or another material like polyester. They’re a very common filter type and are well-suited for typical residential homes. Their MERV ratings vary widely and tend to range from MERV 4 to MERV 15.
  • Fiberglass Filters: Filters made using spun fiberglass. They’re another common filter type and are better suited for homeowners with low filtration needs who need to avoid putting pressure on their HVAC unit. They’re not very effective, and their MERV rating ranges between 1 and 4.
  • HEPA Filters: A highly effective filter type with a medium of folded fiberglass or borosilicate glass. They’re not a widely used filter in residential homes, but can still be used if you have especially high filtration requirements. Their MERV rating spans from MERV 17 to MERV 20.
  • Electrostatic Filters: Electrostatic filters work a bit differently than most. Using a medium of paper and cotton, they create a small electrical charge, which attracts airborne particles. Keep in mind that all pleated filters are electrostatic, but not all electrostatic filters are pleated. Non-pleated electrostatic filters have a typical MERV rating between 8 and 10.
  • Reusable Filters: A reusable filter is a filter type that’s designed to be washed and replaced instead of disposed of like a typical filter would be. Some types are not very effective, with a rating of MERV 1 to MERV 4. However, higher MERVE options are available (up to MERVE 13) if you opt for a reusable electrostatic filter or pleated electrostatic filter.  
  • Carbon Filters: Carbon filters are an unusual filter type. They have a medium of activated carbon, specifically charcoal, which allows them to trap substances known as VOCs, or Volatile Organic Compounds. VOCs are hazardous airborne gasses such as formaldehyde or acetone. A carbon filter doesn’t trap the typical particles a regular filter does, and as such, it doesn’t have a MERV rating, and should not be used by itself.
  • UV Filters: Another filter type that shouldn’t be used alone is a UV filter. UV filters don’t have a medium, but use Ultraviolet light to sterilize the air moving through them. This means that instead of trapping particles, it destroys organic contaminants such as mold spores, pathogens, and bacteria. For this reason, they don’t have a MERV rating.

Myth 2: The Stronger the Better

Another harmful myth is that the stronger the AC filter, the better. This is somewhat true, but it’s fallacious. While stronger filters do filter more particles and improve air quality more, they also have denser material in their medium, which can impede airflow.

If your filter is too strong, it can cause problems for your air conditioner or heater due to the poor airflow. You should get an air filter with a MERV rating strong enough to meet your needs, but not much stronger. How strong of a filter your HVAC unit can handle is determined by factors like its strength and size, as well as the size of your home.

Myth 3: Air Filters Only Trap Dust

Changing furnace air filter
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Some may believe that an air filter will only trap dust. The fact of the matter, however, is that dust is only one of many airborne pollutants that get caught in your air filter. All kinds of small particles, like mold spores, pollen, dander, and dirt get caught in the furnace filter. Some filter types can even trap bacteria and viruses.

Myth 4: Direction Doesn’t Matter

When changing your air filter, it may seem like the direction you place it in is inconsequential. The truth is that the direction does matter for air filtration, as one side of the filter is more porous than the other.

If you install your air filter backwards, it makes it harder for the dirty air to flow through it, which will make your HVAC work harder. The harder your AC unit has to work, the more energy it wastes and the faster it wears out, so always put your furnace filter in the right way.

Myth 5: Filters Only Affect Air Quality

clean and dirty air filters
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Since the main function of an air filter is to remove airborne particulates, you might think that their only impact on your home and HVAC is the air quality. However, this is not true. Your air filter also affects your HVAC’s efficiency, and by extension its lifespan and your monthly utility bill. If you use the wrong filter, or don’t change it often enough, your HVAC will be less efficient, meaning that you’ll spend more and your unit will wear out faster.

Myth 6: Air Filters Don’t Need Frequent Changes

You may believe that you don’t need to change your air filter frequently. While the filter doesn’t need to be replaced every week, you do need to change it on a regular basis. If you don’t change your filter regularly, buildup will clog it over time and reduce its effectiveness.

The exact frequency varies depending on factors like your air quality and the strength of your HVAC system. On average, an HVAC’s air filter needs to be changed once every 30 to 90 days, or one to three months, but you may find yourself having to change your filter more or less frequently.

Myth 7: Pleated Filters Impede Airflow

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Finally, one myth that can be particularly harmful is that pleated air filters can disrupt or impede the airflow in your HVAC system. This, however, is inaccurate. While any particularly strong air filter can disrupt the airflow in your ductworks, there’s nothing about pleated filters in particular that causes this. As long as it’s of the correct strength, you can use a pleated filter without worrying about the airflow in your duct system.

FAQ About Air Filters

Can I run my HVAC without a filter?

No, you should never try to run your HVAC without a filter. Without one, all the debris that the filter would normally catch will make its way into your AC unit, which can have severe consequences in only a few hours. Even a dirty filter is better than none at all.

Can I use two air filters at once?

No. Using two air filters can impede the airflow in your ductworks and affect the performance of your HVAC. It will have to work harder, which will cost you more money, cause your indoor air quality to suffer, and make your AC unit’s lifespan shorter. Only use one air filter at a time.

What should I do if my air filter is moldy?

If you notice mold on your HVAC’s air filter, you need to act right away. It’s likely that more mold is present somewhere in your HVAC, or at the very least somewhere else in your house. You should get a mold remediation specialist to your home as soon as you can so that they can find it and help you get rid of it.

Filter Myths Debunked

If you believe air filter myths, you may be harming your indoor air quality or reducing the efficiency of your HVAC. Do the proper research and find the facts, so that you can keep your air quality and your HVAC’s function up.
If you need help with your air filter, connect with an HVAC professional near you. They can service your air conditioning and heating units so that your indoor air quality stays up and your temperature stays at the right level.

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Austin Geiger

Austin Geiger is a writer who's passionate about home care. He enjoys writing about home maintenance practices, as well as projects to turn an outdoor space into a backyard paradise.