Air conditioning, furnace and heat pumps filter the air at the return to protect the AC system and you. They are rated by their MERV rating which tells you what is being trapped and what is not. So, what does the term MERV rating mean. MERV is the Minimum Efficiency Report Value.

What MERV Rating Should I Use?

• MERV 1 through 4 traps less than 20% at 3.0 to 10.0 microns. A micron is a millionth of a meter. For comparison a human red blood cell is about 5 microns across, your hair is about 75 microns in diameter. This would include pollen, dust mites, standing dust, spray paint dust and carpet fibers.
• MERV 5 through 8 traps between 20 to 85% (MERV 8) and includes mold spores, hair spray, fabric protector and cement dust.
• MERV 9 through 12 will capture particles down to 1.0 to 3.0 Microns. It will capture between 50% (MERV 9) to 89% (MERV 12) and between 85% to 90% of the other 3.0 microns and larger. This includes humidifier dust, lead dust, auto emissions and milled flour.
• MERV 13 through MERV 16 will trap particles between 0.3 through 1.0 microns. MERV 16 harnesses 95% of these particles while the MERV 13 will trap less than 75% and these MERV ratings will trap 90% of the other two categories by micron size. This includes bacteria, most tobacco smoke (all smoke is actually tiny solid particles suspended in the air, and proplet nuceli (sneeze).

Recommended MERV Ratings for Air Filters

ASHRAE or the American Society of Heating, Refrigerating and Air-Conditioning Engineers recommends MERV 6 or higher. DOE, US Dept. of Energy recommends MERV 13. LEED (Leadership in Energy and Environmental Design) suggest MERV 8 as a minimum.

Types of Air Filters for Home

– Disposable Filters are inexpensive fiber glass filled or a polyester mesh and are rated MERV 1 to 4.
– Reusable Filters are of the same materials but are washable and reusable. Rating same as the above.
– Pleated Filters us synthetic materials folded in pleats to increase the surface area and are rated MERV of five to thirteen. High efficiency version go up to MERV 16.
– Electrostatic Filters uses a static electrical charge to attract particles as the pass through the filter’s media. Can be had with MERV ratings up to 15 and are washable and cleanable, there for reusable.
– HEPA (high-efficiency particulate air) carry ratings from 17 up to 20 and can remove up to 99.7% of airborne contaminates. Their design can be two restrictive to allow sufficient air through the return, in short, the system has to be designed to use these filters.

Best MERV Ratings for Furnace Filters

How about furnace filters? They are same as the AC filters. For some systems they will be restricted to lower MERV ratings as they cannot provide enough of a pressure differential to pull air through the more restrictive filters. The higher the rating the more the filter restricts airflow. Most systems can handle MERV 7-12. But commercial building tends to be robust enough to handle the higher MERV rated filters.

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There are other ratings applied to air filters. MPR (Micro-Particle Performance Rating) and FPR (Filter Performance Rating) where created by 3M and the Home Depot. The Home Depot’s FPR rating closely parallels the MERV Rating. For such a simple device it is interesting so much technology and technical ratings go into filters. Contact Air Supply Heating & Air Conditioning for all your HVAC needs.