Residential Air Filters: How do they work?

Residential Air Filters: How do they work?

It may not seem like much, but your furnace filter is an extremely important part of your HVAC system. It protects both you and your furnace. But it’s not like you can just go to the store and grab any old filter. There are lots of choices to make, so to make things a little easier, we’ve broken down a few of the options below. But, first, let’s discuss how the effectiveness of how filters are measured.

MERV Rating

Generally, residential and even some commercial style filters are given a MERV rating to rate the effectiveness of the filtration media. MERV stands for Minimum Efficiency Reporting Value. MERV ratings range from 1 – 20. For example, a standard, blue fiberglass filter would probably be given a MERV 1 or 2 rating, while a white, pleated filter can be rated as high as MERV 16. Basically, the higher the MERV rating the more particles the filter captures. Whichever MERV rating you choose to use in your home is entirely up to you. If you have someone who lives in your home who suffers from asthma and allergies, then you may want to invest in a higher MERV rated filter. If you are more concerned with the amount of air that can flow through the filter then you may prefer a fiberglass filter – it is entirely up to you and whatever filter your HVAC unit calls for.

Types of Filters

disposable fiberglass filters

  • Fiberglass/Cellulose Filters

These are the blue filters I was referencing above. These filters seem to be the most widely recognized but, even within this one category there are several options. First, they can be made of different types of air filtration material, like fiberglass, paper, and advanced nonwoven materials. Beyond that, you have to decide what you’d like your filter to achieve. Depending on the fibers of the air filter media, their size, how tightly they’re woven, and how many layers of media there are, your filter may be more or less efficient at capturing particles and pollutants. Generally, these filters last about a month. So you’ll need to check and change your fiberglass filter monthly.


pleated filters

  • Pleated Filters

Pleated filters perform the same function as the filters discussed above, but are significantly more efficient at capturing smaller particles. They are made of a pleated polyester material. The pleats provide more surface area which increases the ability of the filter to capture particles as air passes through. Some pleated filters are even electrostatically charged to aid in attracting particles to the filter media. There are also deep-pleated filters. These are 4 to 6 inches thick. Again, more surface area to catch the particles we hope to stop from floating around our houses. These filters last approximately three months, depending on use. I would suggest checking how dirty the filter is regularly. Once the filter is too dirty, then it’s time to change it.

hepa filters

  • HEPA Filters

HEPA style filters are even more efficient than the white, pleated filters. HEPA stands for High-Efficiency Particulate Arrestance. These types of filters are generally used in medical facilities, airplanes and even some homes. To be classified as a HEPA filter, the filter is required to capture 99.97% of the 0.3 micron sized particles that pass through the filter. The downside is, not very many HVAC units can operate with a HEPA style filter. You have to have a special type of unit to be able to use this type of filter. However, there are several portable air cleaner units that do accept HEPA style filters. You could use this type of unit in the bedroom of a small child with allergies, someone with asthma, or even just to keep your indoor air as clean as possible.
While air filters aren’t always at the front of our minds, we need to pay close attention to the type of filter we use. They determine the quality of our indoor air and also the health of all individuals who visit or live in our homes.