Understanding Your Air Filter And It's Importance

Technician performing an air filter change out

Your air conditioning system was designed to work within certain static pressures. That simply means that the unit needs to breathe freely. The easiest way to ensure this is to keep your air filter clean. If a unit has a dirty filter it will restrict the airflow and make the fan motor have to work harder. If the dirty filter is left for too long, the dirt can start to accumulate on the evaporator coil and even kill the fan motor. In that case, you're not only going to need to replace the fan motor, but you're going to need a coil cleaning also. Here's what a dirty coil looks like, before and after cleaning:

before and after image of dirty evaporator coil and clean

...and here's what came out of it:

debris that has been cleaned out of an evaporator coil

As you can see, having all of this foreign material accumulating on your evaporator coil can cause all sorts of system problems. This also illustrates how much crud your air filter removes from the air in your home or office. 

So, take this tip; change your air filter every 1 to 3 months and make sure that it is the proper size so no air gets around it, you'll be glad you did.

Top Standard A/C can provide them for you, but here's some useful info for when you are buying filters:

Air Filter Glossary and Terms

  • MERV - Minimum Efficiency Reporting Value. Regulated by standards set by ASHRAE (the American Society of Heating, Refrigerating, and Air conditioning Engineers), every single furnace filter for sale in the US contains a MERV rating. This is the only nationally regulated, independent rating system for air filters.
  • 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.
  • 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 MERV Scale

The MERV (Minimum Efficiency Reporting Value) scale helps you decide about low- vs. high-efficiency air filters. This system ranks filters based on how efficiently they trap air contaminant particles of certain sizes. The higher the MERV number, the more efficient the filter.

  • MERV 1 to 4 – Basic filtration to protect your heating and cooling system.
  • MERV 5 to 8 – Sufficient filtration for those without allergies or asthma.
  • MERV 9 to 12 – Mid-efficiency filtration that helps reduce allergy and asthma symptoms.
  • MERV 13 to 16 – High-efficiency filtration that traps tiny contaminants, such as smoke particles and bacteria.
  • MERV 17 to 20 – HEPA (High-Efficiency Particulate Air) filters that trap bacteria and viruses efficiently enough to reduce the spread of infection.

Here’s approximately how they compare:

Why Higher Efficiency Isn’t Always Better
Choosing low- vs. high-efficiency air filters requires finding a balance between efficient filtration and sufficient airflow. The good news is that filters of MERV 7 to 13 are almost as efficient as HEPA filters, according to U.S. Environmental Protection Agency research.