The Truth About Home Air Filters: 5 Facts You Need to Know

When was the last time you changed your home’s air filter? Most people forget that their home even has one. Out of sight, out of mind, right?

The truth is that the air filter is a crucial component of your home’s HVAC system. But there are a lot of myths going around about air filters.

In this article, I’ll go over 5 things about air filters that every homeowner should know. Some of them sound counterintuitive. And some might surprise you.

Here’s the list:

1. The primary purpose of an air filter is not to clean the air in your home

You read that correctly. The air filter’s primary duty is to protect the HVAC equipment—not to improve the air quality inside your home.

You might think that you’ll get better airflow without an air filter—and that’s partially true. But it only lasts for a little while. 

Without an air filter, there would be all sorts of dust, hair, and grime build-up inside your furnace or central AC. Besides being gross, it’s bad for performance and will quickly wear down your system.

Without an air filter, expect lower performance, higher energy bills, and premature breakdowns of your HVAC system.

2. You don’t need as high of a MERV rating as you think you do

Now that I’ve told you that you absolutely need an air filter in your HVAC system, you should just go out and buy the strongest one, right? Wrong.

The stronger, more efficient air filters will definitely capture more particles. Especially microscopic PM2.5 particles. But with all those extra particles, high-efficiency filters tend to get clogged quickly and need to be changed often.

Combine that with the high price of high-efficiency filters, and you have a money pit that you don’t need to be sinking into.

I recommend using air filters with a MERV rating of around 5 to 8. A MERV rating in this range is a good compromise between air quality and airflow. They are also available in most stores for reasonable prices, so you don’t need to worry about breaking the bank.

Quick Pick
MERV 8 Air Filters

With a MERV 8 rating and mesh-reinforced construction, these filters block most household particles. Since they come in almost any size, these are my favorite pleated air filters to use.

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3. When it comes to air quality, washable filters aren’t as good as pleated filters

If you have allergies or dust issues in your home, then don’t get a washable air filter.

Washable air filters are usually rated in the MERV 1 to 4 range. So they don’t provide as much particle filtration as pleated air filters.

With a washable air filter, you run the risk of letting allergens such as pollen and pet dander slip by—right back into the air in your home.

So why do they even exist? Well, they definitely do capture particles. Some washable air filters are actually pretty great. And using a washable air filter will absolutely help maintain the lifespan of your air handler. You just need to remember to wash them regularly.

4. Size matters—at least for air filters

When was the last time someone told you that size matters? When you’re buying an air filter it does.

The air filter slot in your air handler or return vent is a specific size. So you need to get the exact sizing correct.

Too big? Bad.

Too small? Even worse.

You need to get an air filter that fits just right.

A few common sizes are 20”x20”x1”, 16”x20”x1”, and 16”x25”x1. But you should check the size of your air filter slot just to be sure.

Another way is to look at the filter that is currently installed. Most air filters have their sizing printed on the side of the frame. So you can find an air filter that matches that size and you’ll be good to go.

The size of the air filter is usually printed on the side of the filter's frame.
The size of the air filter is usually printed on the side of the filter’s frame.

5. Changing the air filter regularly is the best thing you can do for your home’s HVAC system

I’m not even kidding. When it comes to taking care of your HVAC system, changing the air filter is the number one thing that you can do.

Why is that? It’s sort of like changing the oil in your automobile. You don’t really notice anything worsening day-to-day. But eventually, all that old oil will start to degrade your car’s performance, and cause other parts in the engine to wear out and break down.

The same goes for your HVAC system’s air filter. Eventually, the filter gets clogged and airflow gets restricted. Next thing you know you’re dealing with poor performance and strain on the whole system—such as the blower, burners, and compressor.

So do yourself a favor and change your HVAC system’s air filter. Set up a schedule and change it on the same day every month, or every two months. You’ll save yourself from headaches in the long run.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

8 thoughts on “The Truth About Home Air Filters: 5 Facts You Need to Know”

  1. When we turn on the heat every year, my husband gets a terrible case of eczema in various spots on his body and especially his face. He changes the HVAC filters every two months and we had the vents cleaned out, nothing seems to help. When we go away for a short vacation, it immediately clears up. This only happens during the winter when we turn the heat on.

    If you have any thoughts, I would love to hear from you. Thank you.

  2. We live in Sac Ca zip 95823. We have a 1120 SF single story ranch style home. 4 on 12 roof pitch. Eight foot ceilings and a cathedral ceiling in the living room. We have a Air Scape Whole House Fan, Attic Fan, and the units Recirculating Fan. We are getting estimates for a new Trade Gas/Electric 2/1 stage roof top unit. It is the 2.5 ton 15 Seer unit. A HVAC contractor said we need to replace out K&N 20x20x1 Thermostatic Air Filter with a regular pleaded 20x20x2. He claims the one we have restricts air flow. He is the only one of six we have spoken to that said it is not a good filter. What is the truth!!


    • Hi Christine,

      Generally the deeper the filter, the better the airflow. So a 2″ filter will provide better airflow than a 1″ filter – all else being equal. However, I’m not sure about the pressure drop of that specific filter. I would go with the contractor’s suggestion since they have had eyes on your system.


    • Hi Christine,

      The main drawback of washable filters is that they get less effective the dirtier they get. So you need to make sure that you clean them regularly- around once a month.


  3. Hi Trey,
    Thank you for your most informative articles! My question is what filter MERV recommendation would you have in the case where I have installed an I-Wave-R. I have been using Filtrete 1500s and they still get pretty dirty after 2 months…
    Thanks again!

    • Hi Katherine,

      My understanding of air ionizers is that they work best in conjunction with traditional air filtration systems. They make it easier for an air filter to filter out small particles.

      I’m not familiar with the I-Wave-R product, so you should consult with the company that installed it in your system to see what kind of air filter they recommend to use with it.

      Hope this helps,


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