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An Unfiltered Series: Air Filters

An Unfiltered Series: Air Filters


We’re often told to “err on the side of caution.” But, what about to “air on the side of caution?” Here at SimpleLab, we think both are important–especially when it comes to your home, health, and everyday environment.

Tap Score Water Test

In this second installment of our “Unfiltered Series,” we take a look at air filtration technology, as we ask:
  1. What kind of filters are out there?
  2. How do they work? and
  3. How do you keep them working?  

Air Filters:

The first thing to consider when purchasing an air filter is its Minimum Efficiency Reporting Value (MERV). This scale is used rate the effectiveness of air filters–the higher the rating, the higher the filtering performance.

In general most recommended MERV ratings for residential filters are between a 7 and a 13. So, keep that in mind as we guide you through the 3 most common types of air filters available.

Fiberglass Filters:

Fiberglass filters are incredibly common these days. You might think that it’s because they are the best–but this is far from the case. Their MERV rating is generally between a 1 and a 4. These disposable filters are not designed to last very long, are not very sturdy, and only filter out large particles.  However, much of the appeal lies in their affordability. They are (generally) the least expensive option on the market–as a single fiberglass filter will set you back about a dollar.

Their filtering material is created through layers of fiberglass fibers (spun glass) that are laid over each other. In general, they catch about 80% of particles ~50 microns and larger, and 25% of particles in the 3 to 10 micron range. When it comes to filtering submicron particles–they only filter 2% that pass through. They function as the minimum protection against air pollution, but because of their large pores, they allow the most airflow through. Unfortunately, they are unable to catch many of the airborne contaminants that can impact your health.

If you are looking for minimal protection and do choose a fiberglass filter, there are a few things to note. Most brands recommend that you change your filter each month–or even more frequently during months when your heater is running more often due to the impacts of forced air.

Polyester and Pleated Filters

Costing around $5 each, polyester and pleated filters do a better filtering job than their fiberglass counterparts. Their MERV rating generally falls between a 5 and 8.

Made of polyester or cotton paper sheets folded into pleats, they come in a variety of sizes (in terms of depth). The deeper the pleats, the higher the degree of filtering. These types of filters trap anywhere from 80 to 90% of particles 5 microns and larger.

Most polyester and pleated filters need to be replaced every few months. Some pleated filters come with wire mesh reinforcement that helps maintain the shape and limit blockage. Stay away  from these ones. It generally means they are a lower quality filter. The better quality filters are made with stronger material and do not need structural reinforcement.

High Efficiency Particulate Arrestance Filters

If you’re looking for some serious filtration action, High Efficiency Particulate Arrestance (HEPA) filters are your best bet.

Through a combination of diffusion, interception, and inertial impaction, HEPA filters are made of an ultra-fine, fiber (usually fiberglass) medium that captures many of the microscopic particles that easily pass through other filters. At the minimum HEPA category, these filters capture 99.97% of 0.3 micron and larger sized particles that pass through. That’s about 300 times smaller than the diameter of a human hair! Make sure the product is “True HEPA”–i.e. actually certified to capture 99.97% of 0.3 microns and larger particles; any “HEPA-like” or “99% HEPA” products aren’t the real deal.

With an average MERV rating between 17 and 20, the clear pro of true HEPA filter are that they capture very small particles. The downside is that replacing filters can be costly and while they do have a long lifespan (between 5 and 10 years), they can break down overtime. It is recommended that you replace your HEPA filter every 2 years. However, the concentration of airborne contaminants, humidity, and temperature may affect the replacement rate.

Air Filter Recap:

Air Treatment Device

MERV Rating


Price Range ($-$$$$)

How Frequently They Need Changing

Fiberglass Filters

Between 1 and 4

80% of particles 50 microns and larger

25% of particles between three and ten microns

2% of submicron particles


Every month

Polyester or Pleated Filters

Between 5 and 8

80 to 90% of particles 5 microns and larger


About every 3 months

HEPA Filters

Between 17 and 20

99.97% of particles 0.3 microns and larger


Every 2 years

A Final Word on Filters….

As we mentioned in part one of our Unfiltered Series–water filters, air filters, (and even Instagram filters) tend to make things better–depending on which one you choose. However, no matter what, it is critical that you maintain and replace them as frequently as the manufacturer recommends. And just remember–#NoFilter isn’t cool anymore.

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