What Makes a Good Air Filter?

This may sound obvious, but filter media is what makes air filters good, or not so good. It’s the “heart” of the filter. There are two main forms of filter media; glass fiber web and plastic fiber web. In a standard residential filter, a glass fiber web is flat and thick enough to fill the frame, whereas the plastic fiber web is pleated similar to a window shade to the height of the frame. Generally speaking, the smaller the fibers and the closer they are together, the smaller the particles the filter will trap. Glass fiber filters have large fibers with large open spaces between them. Plastic fiber filters have small fibers with very small open spaces between them. Pleated plastic fiber filters, therefore, are capable of trapping much smaller particles than flat glass web filters.

Fiberglass (left) and pleated (right) are the two main types of air filters.

Which filter is more efficient?

There is actually an efficiency rating system developed by ASHRAE to help understand the differences in filter efficiency. A fiberglass panel filter, for instance, would typically be MERV 3 to MERV 5 whereas most pleated filters would be MERV 8 to MERV 13. From years of research, the Environmental Protection Agency has identified two standards for the most dangerous particle sizes, PM 10 and PM 2.5. Particulate matter 10 micrometers in size and Particulate Matter 2.5 micrometers in size. They have found that particles that size go deep in the lungs and are difficult to expel. In addition to straining lungs, smaller particles can even cross into the bloodstream and have negative effects on the heart. 

PM 2.5 and PM 10 shown to scale with human hair.

The EPA regards PM 10 particles as general nose and lung irritants that may aggravate or inflame nasal passages and some respiratory systems. PM 2.5 particles have more potential long term damaging effects and can create issues for respiratory sensitive individuals such as asthma and allergy sufferers, infants and the elderly. 

Efficiency graph showing particles trapped by filters with different MERV ratings.

What MERV rating is right for me?

AIRx air filters developed a naming system to condense all this information in a way that could help you identify which filter best fits your needs. Generally speaking, MERV 8 “dust” filters are best suited for protecting your HVAC equipment and reducing visible dust in your home. MERV 11 “allergy” filters are helpful for reducing dust and allergen triggers. MERV 13 “health” filters are best at removing dust, allergens, as well as the microscopic particles that create immediate complications for respiratory sensitive individuals and long term issues in most individuals.

As you can see from the graph, fiberglass filters aren’t very good at stopping much at all.  In fact, studies have shown that air conditioning coils (the cooling portion of air conditioners and furnaces) trap dust at a MERV 6 level. That means, if a fiberglass filter is less than MERV 5, dust can pass right through that filter into your HVAC coils and air ducts. Over time this will build up and clog the coils reducing cooling efficiency and creating a potential for mold growth. If you’ve ever had that “dirty sock smell” when you changed from cooling to heating season, that’s likely dust build up in your HVAC system. You may want to get a system check-up or cleaning and maintain that cleanliness with a pleated filter. You’ll likely save money on energy bills by doing so.

What about airflow?

Another thing to keep in mind is airflow through the filter. Tighter space between fibers traps more particles, but it also means there is less open area for air to move through the filter. If you desire the better particle capture of a pleated filter, make sure to get a filter that is built to industrial standards. This means there will likely be frame support material on both sides of the filter to prevent bowing, but more importantly, industrial-grade filters have more pleated media than inexpensive retail filters. More pleated media allows the filter to hold more dust as well as offering more openings for the air to flow through. Better airflow through the filter frees your furnace or air conditioner to work more efficiently to heat or cool your home, saving you energy costs and possibly avoiding premature HVAC maintenance costs.

Time to replace your air filter?

We hope this information was helpful in understanding the differences between fiberglass and pleated filters. If you’re looking for high-quality filters at great prices, check out our inventory of air filters. We make it easy to find the correct replacement for your system!


3 thoughts on “What Makes a Good Air Filter?”

  1. Your products, timing and info furnished have been highly satisfactory and I will continue to be a customer!
    John A. Meine

    • Hey Sidney! It sounds like you are looking for a fiberglass filter that is 1/4″ thick. Is that thickness including the framing around the fiberglass material?

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