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The Last AC Filter Guide You’ll Ever Need

Air filters are possibly the world’s most compelling topic to discuss, reflect on and consider. HAHA! Don’t worry, I wasn’t being serious.

Now, while not the most thrilling topic to discuss, it is a very important one when considering air conditions inside of your home.  Indoor pollution is a very real thing and can be harmful for you and your family’s health.

According to the Environmental Protection Agency (EPA):

  • Indoor air can be two to five times more polluted than the worst outside air, and it has been ranked among the top five environmental dangers.
  • The average human inhales approximately 15,000 or more quarts of air per day and the average person spends about 90 percent of their day inside.
  • The increasing numbers of children with severe allergies and asthma have been linked to poor indoor air quality.
  • The American Heart Association has linked poor air quality to heart problems and the American Lung Association lists it as a leading cause of lung cancer.

After reading those statistics and terrifying fun facts we can all safely agree we’d rather be taking deep breaths of clean, fresh air and not recycled, stale polluted air.

Heating Ventilation and Air Conditioning (HVAC) systems are awesome at circulating air and air filters do an excellent job of keeping all those nasty things out of our homes, and ultimately, lungs.

So, which air filter should I be buying to keep me and my family healthy? Well, it depends – but everything will be covered in this guide, and we are feeling pretty confident that by the end of all this you’ll know which filter is going to be right for you. Let’s keep this guide as to the point, simple to understand and informative as possible.

1. Furnace Filter Versus Air Conditioner Filter, What’s the Difference?
2. Particulate Matter, What Is It and Why Does It…. Matter?
3. MERV Ratings, What the Heck are They and What Do They Mean?
4. MERV Ratings Are Great But I Still Don’t Know, Which HVAC Filter Do I Need?
5. Bonus Hot Tips
6. Summary

That nifty outline there will allow you to read the parts you’re interested in and skip the ones you’re not. Feel free to jump around.

1. Furnace Filter Versus Air Conditioner Filter, What’s the Difference?

So, we are located down here in the South and regardless of the brand, we call carbonated drinks “coke.” Out west, in California, they call it “soda” and up north they call it “pop.”

It’s the same kind of situation when talking about furnace filters versus AC filters, they are the same thing but depending on where you live, they are probably called a different name.

Which if you think about it makes sense.  In Texas, we suffer through scorching summers where we run our AC endlessly, trying to battle temperatures that are regularly in the 100s. Now if you live in Michigan, summers are more bearable but winters are teeth-chattering cold, with temperatures often falling well below freezing. We tend to refer to HVAC systems in southern states more as AC and in northern states more often as a furnace even though it’s the same equipment. So, whether you are looking for a furnace filter or an AC filter, you’ve come to the right place.

2. Particulate Matter, What Is It and Why Does It…. Matter?

So, we have all seen the little particles hovering around in the air, especially when you look through a ray of sunshine, these little floaty guys are called particulate matter.

Some prime examples of particulate are dust, dust mites, insects, pollen, soot, smoke, skin flakes, pet dander, mold spores, bacteria, and other microscopic pollutants.

Umm… super nasty, but unless you are ensuring that you have a good air filter, you and your family are probably breathing all those things in. Which as you may have already guessed, is not good for your respiratory health or health in general.

Thankfully for all of us, some very smart people have created high-quality filters that can prevent all that gross particulate from getting indoors, circulating and entering into our lungs. There is also a rating system so consumers can make educated buying decisions and know what to expect from their filters when they bring them home. Lucky for us, right? 

3. MERV Ratings, What the Heck are They and What Do They Mean?

Minimum Efficiency Reporting Values, or what most people call MERV ratings, tell you the very least or minimum performance to expect from your filter. They tell how much particulate they can filter out, based on particulate size.

Particulate is measured in microns, which is a unit of measurement for teeny tiny things. One micron is one-thousandth of a millimeter. So you can get an idea of size, a human red blood cell is about 5 microns and human hair is about 50 microns, and the human eye can’t see anything smaller than 40 microns. So, we are talking smaller than “Honey, I Shrunk the Kids” small.

MERV ratings range from 1 to 20, but homeowners only need to be familiar with ratings between 1-16. As the numbers get higher, the more effective they are at filtering out the gross stuff.

All this information sound confusing? Don’t worry, it sounds much more complicated than it is. We’ll break it down-

1-4: These filters are going to give you the most basic filtration. They will trap larger particulate such as hair, carpet and textile fibers, and small bugs. They will only filter out particulate larger than 10.0 microns. They are typically used in window units and residential areas.

5-8: These filters capture particulate matter between 3 to 10 microns. They will filter out dirt, sand and aerosols like hairspray. They are a popular choice for residential homes, workplaces and buildings.

9-12: These filters capture particulate matter between 1 and 3 microns. They will trap legionella, the bacteria that causes pneumonia, flour, car emissions and fumes. They are typically used in specialized commercial buildings and laboratories.

13-16: These filters capture particulate matter between 0.3 and 1.0 microns. They will filter out all bacteria, tobacco smoke and even sneeze particles. These are typically used in hospitals, specialized commercial buildings and smoking lounges.

4. MERV Ratings Are Great But I Still Don’t Know, Which HVAC Filter Do I Need?

Ok, so we’ve got the basics- we know what particulate is and why we care about it, what MERV ratings are and what they filter out. Let’s move on to some more advanced topics like, what filters are made out of and the strengths and weaknesses of each, because not all filters are made equal.

Like most things on this planet, you get what you pay for- unless we are talking about street tacos, because those are always worth it. Generally speaking, the less you pay for a filter, the less it will filter out.

Now, this doesn’t mean you have to immediately throw out those bargain filters you bought last week. But if you have allergies, pets or people at home with compromised immune systems, like babies or ill family members, it may be worth it to replace the ones you have been using and spend a little more next time.


They are made of spun glass and can be found almost anywhere- home improvement stores, grocery stores, etc. They are only capable of capturing large particles from your home’s air. This is probably the least expensive filter option, but they aren’t effective at removing allergens from the air or other small particles.

These filters are disposable and must be replaced every 30 days and have a MERV rating of 1-4.

Washable Filters:

They are made up of a wire-like mesh material. The great thing about these filters is that they are reusable and can last up to 5 years. They are a better choice for the environment because they create less waste than the ones you are throwing away every month. Now just like the name states, they have to be washed around every 30 days. This can be difficult for people that don’t have the time to clean them and let them dry all the way through.

Filters that are put back before drying completely are at risk for growing mold and mildew, which can get into the air supply – yuck. Buying a second filter eliminates this problem, but since they are a pricier option that means a higher investment starting out.

These filters are an exception to the higher price tag higher filtration rule. They are right there with fiberglass filters at a MERV rating of 1-4.

Pleated Filters:

They are made with polyester or cotton fibers that are folded like an accordion, aka pleated, which increases the surface area of the filter. More surface area means more chances to catch contaminants. These are probably the filters you see used the most in homes, and they also remove the majority of stuff on the ick list. However, they can restrict the airflow in some HVAC systems, which can increase operating expenses because the system has to work harder.

These are a step above fiberglass and washable filters with a MERV rating of 6-10. They are disposable and must be replaced every three months.

Electrostatic Filters:

This type of filter has self-charging cotton or paper fibers that attracts air impurities to it. Similar to a magnet, this filter draws dirt, dust and other goobley gunk like pet dander to it, trapping it and keeping it from recirculating in your home.

These filters have permanent and disposable options. Permanent options must be washed when they become dirty, and disposable options usually need to be replaced every 3 months.  If your system needs a custom size, they can get pricey. They have MERV ratings of 8-16.

High Efficiency Particulate Arrestance or HEPA Filters:

These top of the line filters are considered the most effective. These bad boys are made out of 4-5” pleated synthetic cotton that is attached to a rigid metal grid. They are a great choice for people with respiratory problems, severe allergies or autoimmune disease, but are probably more powerful than what the average person needs.

They should only be used with HVAC units that are specifically designed for HEPA filters or are compatible because of their thick size. Because of the amount of moisture and sometimes elevated temperatures, bacteria and mold can grow on the filter and release back into the air. This is unlikely to happen as long as the filters remain clean.

HEPA filters cost significantly more than other filters. They will usually run you around $100, but they have the highest MERV ratings of 13-16.

5. Bonus Hot Tips!

The change times listed above are general suggestions of when it is best to clean out filters but always consider your unique circumstances.

  1. If you live in the South, you are most likely running your HVAC system more in summer months. You will probably have to change your filter more frequently during these months, but if you live up North, you are probably running your system more during cold months.
  2. If you live in a city with more pollution or an area with a lot of dust, your filter will probably fill up with icky stuff faster.
  3. If you only have one filter for your home, that one filter has a big job. That filter will need to be swapped out or cleaned more often than larger systems that have more than one filter.
  4. If you have bad allergies, during the months that the allergens are the most present you will want to change the filter more frequently to ensure it is working its most effective. This will help to prevent you from being all itchy and sneezy.

6. Summary

Wowzas! That is a lot of information to chew on all at once, but for the sake of due diligence let’s do a quick recap.

  • Indoor pollution has been linked to allergies, asthma, heart disease and lung cancer.
  • Particulate matter is that nasty stuff that floats around in the air that no one wants to breathe in. Prime examples – dust, dust mites, insects, pollen, soot, smoke, skin flakes, pet dander, mold spores, bacteria, and other microscopic pollutants.
  • MERV ratings range from 1-20 and give you the expectations for the filters in that rating, telling you the minimum that filters will remove from the air. Homeowners only need to worry about 1-16.
  • You get more filtering bang for your buck. The more a filter costs, the more it filters out of air (excluding some reusable filters).
  • Different filter materials will have different downfalls and advantages. Your budget, lifestyle and preferences will determine which filter type will be your best bet.
  • Change your filters often and consider your unique circumstances. The suggested change time may not be right for you.

Now, with all that said. No guide is perfect, and it is possible you’re left with some lingering questions because everyone has different needs when it comes to HVAC systems… Which is all good, because ISC Sales has some very knowledgeable people that are on standby to help you.

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