Things to Know About MERV and How It Affects an HVAC System
Air filters vary in rating based on material: fiberglass and washable types are MERV 3-4, blocking larger dust; pleated paper filters have finer pores, providing better filtration at MERV 5-8.
Changing an HVAC system’s air filter is a necessary task that will eventually require attention. However, changing a filter isn’t as simple as swapping out the old one for a new one. The design and manufacture of an air filter involve significant complexity, given its integral role in keeping indoor air free of harmful airborne particles.
With numerous types of air filters available, selecting one that offers optimal performance can be challenging. MERV provides a way to compare air filters to find the one that meets specific filtration needs.
What Is MERV?
MERV stands for “Minimum Efficiency Reporting Value.” It is a set of testing standards that determine how well air filters perform at capturing dust, pollen, and a variety of other airborne pollutants, including cigarette smoke, bacteria, and viruses.
Essentially, MERV is a useful comparison tool for determining which air filter is likely to perform best in an HVAC system. Although MERV is the leading standard for most air filter manufacturers, some retailers use their own custom rating systems for filters sold in their stores. These systems might not be compatible with MERV.
How Does MERV Work?
HVAC air filters using the MERV standard undergo several tests, covering airborne particles as large as 10 microns to particles as small as 0.30 microns. Each test uses a particle generator that sends synthetic dust particles of a specific size through the air filter. Testers then compare particle counts upstream of the filter with those measured downstream.
A typical air filter undergoes six passes, starting with a clean filter. Each successive pass allows the filter to become progressively dirtier, simulating performance under normal use. For accurate testing, the equipment must undergo 13 qualification tests for accurate calibration and standardization under laboratory conditions.
After thorough testing, the filter is given a value used to compare one air filter’s overall performance to another. These values are based on a scale of 1 to 16 for most standard HVAC air filters.
What Does MERV Mean for an HVAC System?
MERV provides a quick way to compare several HVAC air filters simultaneously. Instead of analyzing test results for hours in search of the best air filter, MERV allows for a quick narrowing of search results, enabling a focus on other factors like price and build quality.
When planning to upgrade a current air filter, its MERV rating indicates its performance level and how far an upgrade can improve indoor air quality. For example, if the current air filter is rated at a MERV of 3, upgrading to one rated at a MERV of 7 or higher can significantly improve air quality and the HVAC system’s overall performance.
However, a high MERV rating doesn’t necessarily guarantee superior performance for an air filter. The MERV rating indicates which particles are filtered and helps customers decide which particles they want filtered out. Some filters offer increased filtration performance at the expense of airflow. An overly constrictive air filter for an HVAC system can lead to increased wear and other mechanical issues throughout its working life.
Common Ratings for HVAC Air Filters
The material of the air filter can affect its rating. Most fiberglass HVAC air filters and the majority of washable air filters are rated at a MERV of 3 or 4. These filters can block large dust and debris particles, but their pores are usually too large to capture anything smaller. Pleated paper filters have smaller pores in comparison, offering better filtration performance and a higher MERV ranging from 5 to 8.
Pleated air filters rated at a MERV of 9 through 12 offer better performance, capturing up to 90 percent of particles as small as 1 micron. These filters are capable of trapping mold spores and volatile organic compounds (VOCs) and can also trap Legionella droplets. Filters rated between a MERV of 13 and 16 go further by trapping bacteria droplets and other dangerous particles as small as 0.3 microns.
Some HVAC air filters can exceed the MERV scale, such as HEPA filters intended for use in medical and industrial settings. Despite being exceptionally effective at capturing virus droplets and other harmful airborne particles, these filters can prove heavily restrictive in most residential HVAC units unless significantly modified to overcome airflow constraints.
Fix My Air DFW of Fort Worth specializes in residential and commercial HVAC services, including routine maintenance, installation, and repair. All makes/models. Call us at (817)839-3511.
