Here's How to Understand HVAC Air Filter Ratings
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Here’s How to Understand HVAC Air Filter Ratings


Choosing the right filter for your HVAC system can be a time-consuming and confusing task if you’re not well versed in industry acronyms and filter ratings. This brief primer can help clarify what they mean, so you can select the best HVAC air filter for your needs.

MERV — The Key to HVAC Filter Efficiency

HVAC air filters are rated using the minimum efficiency reporting value or MERV scale. This numerical rating goes from 1 to 20, and it measures a filter’s ability to capture particles in a certain size range. The higher the number, the better a filter performs.

HEPA — What Does it Mean?

Another frequently-heard air filter term is HEPA, which is an acronym for high-efficiency particulate arrestance. These filters top the MERV scale with ratings from 17–20. They’re capable of capturing as much as 99.97 percent of undesirable particles as small as 0.3 microns. However, they’re not used in residential HVAC systems because they also severely restrict airflow.

How to Choose the Right Filter

If you’re unsure about which filter to use, it’s best to follow your manufacturer’s guidelines on the MERV rating range for your equipment, or ask your HVAC technician. As a general guide, here’s how different types of filters rate:

  • Flat fiberglass — These inexpensive filters have MERV ratings from 1–4. They’re best used to keep harmful particles out of the HVAC system. They can only trap about 80 percent of particles 10 microns and larger so they don’t really boost air quality.
  • Pleated — Considered “medium-density” because of their greater surface area, these filters go from MERV 5–13. The higher-rated versions are better at improving air quality because they can trap up to 95 percent of particles down to 3.0 microns in size.
  • Higher-efficiency — These fiberglass filters range from MERV 14–16, but if you want to use one, you’ll need to discuss modifying your HVAC system with a knowledgeable contractor because they can hinder vital airflow and cause significant equipment damage.

For expert advice about which HVAC air filter is ideal for the system in your Portland-area home, contact us at Roth Heating & Cooling.

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