Find out why the highest MERV rating isn’t always best.
Most people are familiar with some of the terms associated with an HVAC system, but many have never heard of MERV. What does MERV mean?
MERV stands for “minimum efficiency reporting value,” which is the system used for rating air filters. Measuring how efficient an air filter is at removing particles from a home or business and rating the filter from 1 to 16 lets you know which ones perform the best.
What the Numbers Mean
Designed by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the MERV scale was actually originally created for identifying which filters performed the worst when removing very small particles from 3 to 10 microns. One micron is 0.00004 inches.
Unlike other ratings for heating and air conditioning systems, a higher number does not necessarily mean better. The MERV for home systems should be between 7 and 12 for the most efficient removal of airborne particles. A higher rating from 13 and 16 is the best for commercial use such as in hospitals.
The numbers refer to the holes in the filter through which the air flows. Higher numbers mean smaller holes. This does not necessarily mean they are better because in residential settings this can restrict air flow, reducing the performance quality. This can lead to higher energy costs and the need for more frequent AC repair. Low numbers can also cause a problem because they can allow dust, carpet fiber, dust mites, bacteria, and other contaminants into the unit which defeats the purpose of the filter.
How the MERV Rating is Decided
Tests are performed on the filters to determine its MERV rating. In a testing area, technicians introduce particles of various sizes into the air. There are twelve sizes in total, with the smallest being from .3 to .4 microns and the largest from 7 to 10 microns.
Measurements of the thickness of the particles are taken before and after they pass through the filters. This allows the technicians to know the effectiveness of the filter when removing different size particles. The test is performed a total of six times for each of the twelve sizes and the worst result is the one used for the MERV number.
Maintenance and the MERV Rating
HVAC technicians can advise you on the right filter for your HVAC system, including the correct MERV rating. Small air conditioning unit filters do not have a MERV rating. This is only used for larger systems. One thing you should keep in mind is the filters will remove particles from the air even though their main purpose is not to improve the air quality of your home or business.
Yes, the filter can trap these particles but they are going to be in the system regardless. The purpose of a filter is to keep your heat and AC unit clean and protect it from debris that can get into the system, causing it to malfunction, work harder and result in higher energy costs.
When the system is in use, it is important to change the filters regularly. Dirty filters restrict air flow and cause damage over time that is expensive to repair. Compressors are one of the parts of the air conditioning system that suffer from restricted air flow.
A filter with the proper MERV rating is one of the best ways to keep heat and air systems functioning at their peak levels. Another is to set up a maintenance schedule with a technician to keep your HVAC equipment in the best shape possible.
MERV numbers are reliable particularly because of the testing. This rating is the result of thorough testing. The final number used for the rating is the worst result so it’ not exaggerated. This is something that should definitely be considered when choosing air filters for your HVAC system. Keep in mind that the highest MERV is not always the best.
