HVAC, MERV, HEPA—there are so many four-letter initialisms to navigate, when all you want to do is breathe without sneezing. If you’re moving into your first home or you’ve noticed your existing home is hardly a fortress against the allergies you expected to leave outside, you’re probably exploring some of these acronyms and what they mean. HEPA and MERV refer to two standards of air filters that could address your needs. Here, we’ll explore HEPA versus MERV filters and the differences between them.
We’ll begin with the obvious: MERV has nothing to do with singer and television personality Merv Griffin. Rather, as you may have guessed, MERV is an acronym for “minimum efficiency reporting value.” There’s not a single “MERV filter,” per se, but rather a MERV rating assigned to a variety of air filters. A filter’s MERV rating tells you how many particles it allows to pass through in a worst-case scenario—the minimum efficiency, in other words. The MERV scale runs from 1 to 16, with 1 being the lowest efficiency and 16 the highest. However, MERV ratings 13 through 16 are traditionally reserved for specific industrial applications such as clean rooms or laboratories, leaving a twelve-point scale for residential air systems.
More specific than the wide-ranging MERV scale is the designation of HEPA—high-efficiency particulate air. A HEPA filter has a specific construction that significantly limits the particles that pass through. To attain true HEPA status, a filter must capture over 99.9% of all particles more than 0.3 microns wide. This superior filtration makes HEPA filters the choice of hospitals, labs, and other settings where clean air is imperative. However, such heavy filtration comes with drawbacks. Remember that filtration isn’t free—the resistance a filter places against airflow means the HVAC system must work harder. Some level of filtration is always necessary, but in residential HVAC settings, the high resistance of a HEPA filter can place such undue strain upon the system’s fan as to make its installation counterproductive.
Which Way To Go?
Depending on the sensitivity of the people in your household, you may benefit from embracing both HEPA and MERV filters. The differences between them can complement one another for a thoroughly well-filtered home. Portable air purifiers that use HEPA filtration are available for treating the air in single rooms. This can be preferable to installing a HEPA filter on a central HVAC unit that isn’t built to withstand the filter’s high resistance. For your home’s HVAC system, you’ll likely find that many 20x20x1 AC filters with MERV ratings of 7 and above will capture the mold, dander, dust mites, pollen, and loose carpet fibers that trigger so many allergic reactions. Think MERV for central air and HEPA for peripheral.