MERV Ratings: What Do They Mean?

MERV Ratings

Photo: Sympiontservice.com

When we set out to build a new construction home, we had a lot of research to do. Having lived in NYC apartments for the previous 20 years made the job a lot harder. We’d always relied on a superintendent to think about the furnace, the water heater, and all the other systems that made our building run. So we had a lot of catching up to do.

Related: The Meaning Behind GREEN

Now that our home has been built, we have begun doing regular maintenance on our HVAC system. In the process, we’ve been faced with something called a MERV filter. MERV? Like, Griffin? Or is that some robot from Star Wars? I had no idea. So for the uninitiated (like I was), here’s a quick primer on MERV ratings and what they mean:

What Is MERV?
MERV stands for Minimum Efficiency Reporting Value. Or in English, “how effective is your air filter?” MERV ratings range from 1-16. The higher the MERV rating on a filter, the fewer dust particles and other contaminants can pass through it. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) designed the MERV scale to represent a filter’s worst possible performance at removing particles .3 to 10 microns in size (that’s really small!).

Some of the common particles that filters are tested for include pollen, dust mites, textile and carpet fibers, mold spores, dust, pet dander, bacteria and tobacco smoke. Most residential systems can adequately remove airborne contaminants with a filter rated MERV 7-12. MERV 13-16 is typically found in hospital and general surgery settings.

What do MERV Ratings Mean?

Illustration: Filterfast.com

Higher Is Not Better
You might think that a higher MERV rating would automatically be better, but it’s not. The higher the MERV rating, the smaller the pores are for air to flow through an HVAC filter. This can create more resistance in airflow than a system is designed to manage, thus making it inefficient. Reducing the air flow in your system can actually worsen the air quality in your home and put a damaging amount of pressure on the fan of your furnace or AC system. So it is worth doing some research. Find out what the highest MERV rated filter is that still allows for maximum airflow in your system.

Change Filters Often
Filters with higher MERV ratings need to be changed more frequently (at least every three months) to avoid restricted airflow that can cause your system to work inefficiently or possibly even damage it.

We discovered that our MERV filters are a custom size, which makes them about three times more expensive than standard-size filters you can buy at big box stores. When you’re changing filters four times a year, that really adds up. So if you’re working with a builder to design a system, keep that in mind. As has happened so many times in this home-building journey, I discover I don’t even know what I don’t know! But figuring out what that MERV rating on my filter actually means does make me breathe a little easier.

For more on HVAC filters, consider:

How To: Choose the Right Furnace Filter
What You Might Not Know About HVAC Filters
Quick Tip: Improve Your Home’s Indoor Air Quality