Filters are used in:
- Vacume Cleaners
- HVAC filters
- dust masks
- smoke hoods
- Auto air filters

This page is primarily about Heating Ventilating and Air Conditioning (HVAC) filters

• Protecting the motors, fans and coils of HVAC systems from getting a buildup of dust, dirt and debris
• Keeping your house clean by removing dust and lint particles
• Protecting your health my removing allergens and some micro organisms

There several kinds of HVAC filters.

• Fiberglass filters - Trap larger particels including some dust. They are cheap, but be replaced monthly.
• Electrostatic Filters - Use static electricity to remove particles from the air. The front of the filter charges any particles with static electricity. Then, as the particles move through the they are attract and stick to the rear layers.
• They are equivalent to a MERV 4-9, but claim to be better at removing allergens. They cost from $150 - $450, so are cheaper in the long run, but need to be washed every month or so.
• Pleated filters - Made of a polyester fabrics or cotton with MERV ratings typically from 8 - 16. They gain efficiency because they have an increase in surface area.
• UV Filters - Use ultraviolet lights to kill bacteria and viruses in your home.

Carbon Layers made of activated carbon, also called activated charcoal, carbon air filters can help trap odors.
How It Works: Carbon Filter | 3M

MERV Rating (Minimum Efficiency Reporting Value) EPA

MERV is the primary rating system used in the industry, both domestically and internationally. Established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, MERV rates a filter’s ability to capture and hold particles and pollutants.
See below.

MPR (Micro-Particle Performance Rating) - A rating system developed by 3M (sold at Lowes). It rates the manufacturer’s filters and their ability to capture airborne particles smaller than 1 micron

FPR (Filter Performance Rating) - A rating system developed by The Home Depot for brands sold through their stores, including Honeywell. It utilizes a color and number scale from 4 to 10 that closely resembles MERV rating

HEPA (High Efficiency Particulate Arresting Filters) are a popular filter type used in indoor air cleaners and vacuum cleaners. They represent state of the art technology and are one of the most efficient types of air cleaner filters used for general air cleaning. By definition, a true HEPA filter in contrast with a near HEPA filter, must remove 99.97% of all particles of 0.3 microns mean diameter.
That micron size (0.3) is referred to by scientists as the MPPS, or the most penetrating particle size. Scientists have found that particles of that size evade air filters more than larger or smaller particles. We’ll get into why in a little bit.

MERV Rating (Minimum Efficiency Reporting Value)

MERV is the primary rating system used in the industry, both domestically and internationally. Established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers, MERV rates a filter’s ability to capture and hold particles and pollutants.
8 = Standard; 11 = Superior; 13 = Best
The company which installed my Lenox system recommends 11, but says you can use 16 if you want to filter many viruses.

MERV Value	Av. Particle Size Efficiency			Types of things trapped
	0.3 - 1 Micron	1 - 3 Micron	3 - 10 Micron
MERV 1	-	-	Less than 20%	Pollen, dust mites, standing dust, spray paint dust, carpet fiber
MERV 2	-	-	Less than 20%
MERV 3	-	-	Less than 20%
MERV 4	-	-	Less than 20%
MERV 5	-	-	20% - 34%	Mold spores, hair spray, fabric protector, cement dust, animal dander, and dust mite droppings (highly allergenic)
MERV 6	-	-	35% - 49%
MERV 7	-	-	50% - 69%
MERV 8	-	-	70% - 85%
MERV 9	-	Less than 50%	85% or better	Good for homes with occupants who have COPD, allergies, astma and other respiratory conditions. Humidifier dust, lead dust, auto emissions, milled flour. Almost as effective as HEPA filers
MERV 10	-	50% - 64%	85% or better
MERV 11	-	65% - 79%	85% or better
MERV 12	-	80% - 89%	90% or better
MERV 13	Less than 75%	90% or better	90% or better	Viruses, bacteria, most tobacco smoke, proplet Nuceli (sneeze) and carbon dust. Used in commercial manufacturing operations. Bacteria,
MERV 14	75% - 84%	90% or better	90% or better
MERV 15	85% - 94%	90% or better	90% or better
MERV 16	95% or better	90% or better	90% or better

Source: What does MERV Rating mean | CoolRay.com

According to Sun Kool AC, Inc. a residential system will not accommodate filters with MERV ratngs above 12 without modifications.
The company which installed my Lenox system said that is not true.

True HEPA filters with a MERV between 17 and 19 are defined by the Institute of Environmental Sciences and Technology. (IEST) method as having a minimum efficiency between 99.97% and 99.999 % in removing 0.3 μm particles.
A MERV of 20 is rated for 0.1 - 0.2 μm particles.
Source: HVAC-Talk.com

Particle size:
Dust: 1-12 micron
Bacteria: 0.2 to 20 micron
Smoke: 0.01 - 1 micron
Virus: 0.02 to 0.4 micron [rhinovirus (cold) = 0.02 μm, Flu = 0.1 μm]
μm = micron
See Size in reference.

MERV (Minimum Efficiency Reporting Values) MERV Rating Average Particle Size Efficiency in Microns 1-4 3.0 - 10.0 less than 20% 6 3.0 - 10.0 49.9% 8 3.0 - 10.0 84.9% 10 1.0 - 3.0 50% - 64.9%, 3.0 - 10.0 85% or greater 12 1.0 - 3.0 80% - 89.9%, 3.0 - 10.0 90% or greater 14 0.3 - 1.0 75% - 84%, 1.0 - 3.0 90% or greater 16 0.3 - 1.0 75% or greater What is MERV rating (Minimum Efficiency Reporting Values) | EPA

MPR (Micro-Particle Performance Rating) - A rating system developed by 3M (sold at Lowes). It rates the manufacturer’s filters and their ability to capture airborne particles smaller than 1 micron

FPR (Filter Performance Rating) - A rating system developed by The Home Depot for brands sold through their stores, including Honeywell. It utilizes a color and number scale from 4 to 10 that closely resembles MERV rating

* MPR is used by 3M (ACE and Loews), FPR is used by Honeywell (Home Depot)

MERV	MPR*	FPR*	Efficiency	Frequency
6	300	n/a	Captures dust and pollen	30 Days
7		5		30 Days
8		4	Dust, pollen, dust mites, lint	90 Days
10		7-8	Dust, pollen, dust mites, lint	90 Days
11		7		90 Days
12		9-10*	MERV 8 + mold spores, bacteria, smoke, pet dander	90 Days
13	1900	10	MERV 11 + virus carriers and odors	90 Days

* When there are 2 MPR ratings e.g. MERV-12, FPR 9 or 10
The 9 is for the Nordic Pure; the 10 is for the Honeywell.

Source: Best Air Filters for Your Home - The Home Depot

I copied this chart from a label in the store on the same day as the above. They seem to be inconsistent. The char above shows the MERV 13 has odor elimination, but the one below does not. Their web site indicates the MERV 11 filter is the only one with a carbon layer.

Filter at Lowes (click to enlarge)