A&M Heating and Air Conditioning News


The main purpose of a filter is to protect the blower, motor, wheel, evaporator coil, and condensate drain. It protects the system from all the dust, hair, and other gunk the return duct pulls in. While it will also help the quality of the inside air (as it is removing contaminants from being recirculated), its primary job is not to actually clean the air as many people believe. To keep a system working to its optimal performance the filters need to be changed on a regular basis. Sounds simple, but in reality, there are so many options for filters that choosing the wrong one can do more damage to a system than good and could potentially cause a system to break down.

  • The poorest filters (least expensive) are ones with a slight sticky surface on one side. Once particles are stuck to the sticky surface all other particles will pass through, and the filter no longer works. These filters are efficient for a month or less. If not changed monthly the internal components will become dirty causing the system to work harder and eventually malfunction.
  • The high-end rated filters (most expensive) allow less air to flow through and can force the system to work harder and possibly malfunction

There are three filter rating systems created by separate organizations… MERV, MPR, and FPR.

  1. MERV – Minimum Efficiency Reporting Value. Regulated by standards set by the American Society of Heating, Refrigerating, and Air conditioning Engineers, this is the only nationally regulated, independent third-party rating system for air filters.
  2. MPR – Microparticle Performance Rating. The MPR system of ratings was created by and is only used by 3M. Only filters under the 3M / Filtrete brand contain an MPR rating.
  3. FPR – Filter Performance Rating. FPR is a proprietary system developed and used only by filters sold at The Home Depot. They made the switch from MERV several years ago.

The difficulty here is in comparing the name brand MPR and FPR ratings to MERV ratings. Because MPR and FPR do not release their third-party testing, the consumer is left to guess what a 3M or Home Depot filter is equivalent to in MERV. It is also interesting that 3M commercial filters use the MERV rating – not their MPR rating system. This makes it suspect that the MPR and FPR ratings are used as marketing propaganda to promote their “name” brands without having to comply with the MERV rating system. The chart below shows MERV ratings which range from 1-16.

MERV Rating Air filter will trap air particles size .03 to 1.0 microns Air filter will trap air particles size 1.0 to 3.0 microns Air filter will trap air particles size
3 to 10 microns
Removes these particles
MERV 1 < 20% < 20% < 20% Pollen, dust mites, spray paint, carpet fibers
MERV 2 < 20% < 20% < 20%
MERV 3 < 20% < 20% < 20%
MERV 4 < 20% < 20% < 20%
MERV 5 < 20% < 20% 20% – 34% Mold spores, cooking dusts, hair spray, furniture polish
MERV 6 < 20% < 20% 35% – 49%
MERV 7 < 20% < 20% 50% – 69%
MERV 8     70% – 85%
MERV 9 Less than 50% 85% or better Lead dust, milled flour, auto fumes, welding fumes
MERV 10 50% – 64% 85% or better
MERV 11 65% – 79% 85% or better
MERV 12 80% – 90% 90% or better
MERV 13 Less than 75% 90% or better 90% or better Bacteria, smoke, many viruses
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

A&M recommends MERV 8 as the most economical and efficient for most systems. These filters need to be changed on a regular 3-month basis. This is the industry recommended standard. The best guess price comparison to MPR (3M/Filtrete filters) is their 1085 series and the Home Depot FPR filters would be their Honeywell FPR 7. An alternative to purchasing in a store is to subscribe to an on-line filter manufacturer who would deliver the needed filter(s) every three months for installation. This would ensure the MERV 8 filter rating as well as be a reminder to change the filter when it arrives. Three highly rated manufacturers who provide this service are Air Filters Delivered, Factory Direct Filters, and Discount Filters.

Matt R

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