Although a MERV rating (which stands for Minimum Efficiency Reporting Value) might sound complicated, it really just tells you how effective your air filter is in comparison to other air filters on the market.

For residential settings, like your home or office, MERV ratings go from 1 to 13, with MERV 13 being the highest rated filter for a domestic environment.

(ASHREA Tested MERV ratings actually go up to MERV 16, but 13-16 are usually for factories and medical environments with systems that are designed to handle the airflow restriction these filters will cause.)

The MERV rating indicates how effective the filters are at removing different size particles from the air you breathe.

At the top end, MERV 11 to 13 removes the most particles and contaminants — from the visible ones like smoke and dust to pollen and other microscopic allergens — from the air you breathe, while MERV 1 filters are good for providing maximum airflow while still removing some of the larger particles like dust and pollen.

On a more scientific level, MERV 11 to 13 filters can capture particles from 10 microns to as small as .30 microns from the air, while MERV 1 filters can capture particles that are closer to 10 microns in size.

For scale, 100 microns is about the thickness of a human hair, so even MERV 1 filters can capture particles that are very small.

It’s a common misconception that you should always choose the filter with the highest MERV rating.

And, on the surface, it makes sense: a higher MERV rating means fewer particles and contaminants in the air, which equals better air quality.

However, as you increase the MERV rating, you decrease the size of the holes that allow air to flow through your HVAC filter.

If your system wasn’t designed to handle a filter with a high MERV rating, this can reduce the airflow into your home, affecting the air quality and — in some cases — causing damage to your furnace.