Skip navigation

Serving Northern California Since 1946

Serving Northern California Since 1946


DeHart Plumbing, Heating, and Air Inc. Blog

Understanding the MERV Rating and Air Filters


Air filtration systems are one of the basic building blocks of indoor air quality for a home. We offer many types of IAQ services for our clients, but air filtration in Modesto, CA solutions are one of the most common. Among the top systems we install are PureAir S, the Carbon Clean 16, and the Clean Air 11.

However, finding the right air filtration for a home isn’t something we do by selecting the most powerful filters available. That can lead to serious problems with the HVAC system in the house. We take into account many factors when it comes to choosing air filters. One of the key factors is MERV, the rating system measuring air filter strength. To help understand the importance of finding the right air filters, we’re going to go into more depth about MERV.

The MERV Basics

MERV stands for minimum efficiency reporting value. The measurement for filter strength and how to test it was created in 1999 by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). The older measurement ASHRAE used was often confusing to customers, so MERV was adopted. The new tests are done by measuring the effectiveness of a filter with 12 different sizes of particles. A MERV number is then assigned to the filter based on these tests, ranging from 1 to 16. The higher the number, the more effective the filter is at trapping smaller particles.

A MERV 1 filter has an efficiency of less than 20% on particles between 3–30 microns in size. Further along the scale is MERV 16, with 95% efficiency on particles down to 0.3 microns in size. So there is a wide range of differences along the scale—and it goes up to 20.

Filters that are MERV 1–4 are the types found in window air conditioning systems or the standard furnace filter use to protect the interior of the furnace from large contaminants but aren’t very effective on anything smaller than 10 microns.

MERV 5–8 filters are the ones most often installed into homes and some commercial buildings. They’re effective at stopping pollen, dust mites, the lint from carpet and furniture, and dust and most particles down to 3 microns.

MERV 9–12 filters are the top-line for residential uses and are used in larger commercial and medical buildings. These filters can stop many fine particles down to 1 micron in size.

MERV 13–16 filters are rarely used in homes. They are used for surgery rooms, hospital in-patient rooms, computer clean rooms, and other industrial uses. They are strong enough to stop bacteria.

The reason it’s important to match a home’s HVAC system with the right MERV is that we can’t err on going too strong, because it will limit the efficiency of the HVAC system because of the resistance to airflow. We will match your house with the most powerful filter possible that will not create problems for your comfort and damage the HVAC system. To help remove any particles that the MERV rating of the filter will not effect, we can pair the filter with an air purifier.

“Live Green, Save Green!” Greenhart serves Modesto, CA and the surrounding areas. Get in touch with us for the right air filters for your house.

Comments are closed.