MERV Ratings: Who Is Merv and Why Is He Weighing in On Your HVAC Filters?

Minimum Efficiency Reporting Value (MERV) Is A Thing and You Should Probably Know About It

air filters, indoor air quality

When it comes to selecting what air filter will be the most effective, we’ll admit the process can be confusing for people. Very confusing. In fact, if you’ve decided to replace the HVAC filters yourself, one trip to the hardware store can feel like four years at a major university. Choices abound, all with these pesky “MERV” ratings attached to the label. Is the highest rating the best? How do they rate it? And who the heck is Merv?

Blame the folks in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). Honestly, they’re just trying to help. These minimum efficiency reporting values measure how well an air filter can trap .3 to .10 micron-size particles from the air that passes through it. As you might guess, most pollens, household irritants like pet dander and cigarette smoke, molds, and plain old dirt happen to float around at exactly this size. And an air filter with a MERV rating of just 7-12 will remove quite a bit of this environmental garbage from the air you breathe. That’s what most residential systems recommend, and what you should look for at the store.

Now, because we’re a species of overachievers, you may think that higher MERV ratings are even better. If your filter already is at a 7-12 rating and the scale goes up to 16, why not go for it and buy a filter at the top of the MERV scale? After all, filters with a 13-16 MERV rating are used in hospitals and other environments where sanitary conditions are paramount, so why wouldn’t you want that same standard at your home or office?

Here’s the rub. It doesn’t quite work that way. The higher the rating, the less porous the filter. Filters with a 13-16 MERV rating block quite a bit of airflow, to the point that special equipment that can accommodate this resistance is needed. For the average home HVAC system, a high-rated MERV filter could actually put a strain on your furnace and/or air conditioner, to the point of breakdown. Air pressure imbalances occur, and the end result is poorer air quality than you would have achieved with a lower rated filter. In other words, don’t choose a filter that wasn’t designed to work with your HVAC system. Leave the super-specialized air filtration systems to the hospitals and environments that depend upon them.

Still worried about air quality? When you understand the secrets of MERV, you can remain vigilant against environmental pollution by changing your standard filters every three to six months to maximize their effectiveness. Once you check with a professional HVAC specialize to ascertain the exact size and model you should be getting, you can look around for the lowest price to buy in bulk, either online or at a big box store. Make appropriate MERV-rated air filter changes a regular part of your HVAC maintenance, and you’ll enjoy indoor comfort and great air quality all year round.

Ensure your HVAC system is filtering out pollutants and saving energy. Call Air-Tro today. We’ve been keeping California comfortable since 1969. (626) 357-3535.