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How often should I replace my furnace air filter?

FILTERSCAN WiFi Air Filter Monitor
View the FILTERSCAN Informational Video
Manufactured by CleanAlert, LLC

How often replacing, changing, or cleaning an air filter for your home or building furnace, air conditioner, heater, or HVAC system depends on your home or building environment. There are many factors that lead to air filter dirt build up and clogging. Let’s define the difference between dirty and clogged. As an air filter collects dust and dirt particles, the path of the air flowing through the air filter becomes more restrictive. At first, this buildup of dust and dirt make the air filter “look” dirty to the eye. However, at the early stages of “dirtiness” the air flow is not being restricted significantly. So, The HVAC system runs normally. Later in the air filter’s life, the dust and dirt particles build up to a point where the air flow starts to become more restricted, and, over time, becomes so clogged that the HVAC system can no longer provide enough air flow to properly heat or cool the home or building. Now, before that point, during the life of the air filter, the pressure within the HVAC system ducts (across the air filter) increases. First gradually while the air filter is “dirty”, then more rapidly as more dust and dirt build up. Then, finally, to a point where HVAC system damage can occur, causing hundreds or thousands of dollars in repairs. The HVAC industry has adopted a point of pressure where the air filter should be serviced (cleaned or replaced). That point is where the pressure has doubled from its original clean air filter state, and is typically measured in inches of water column or inches w.c. and typically in the range of 0.10” w.c. to 0.50” w.c. (for household HVAC systems).

So, how often should an air filter be replaced? Ask yourself these questions:

  • How often is the system is running, whether from manually turning the system on and off, setting the temperature either a few degrees or several degrees relative to the outside temperature?
  • Is the system used for both heating and cooling?
  • How clean is the indoor air? Are there pets shedding fur and dander?
  • Is there remodeling or construction going on within the home or building, or even in the neighborhood? Construction dust can readily fill the interior air and be captured by the air filter, causing clogging at a faster rate than normal.
  • Is it the time of year for pollen floating in the air? Assuming your home or building is not air tight and that doors and windows are opened periodically, pollen can easily enter the interior air space and drawn into the air filter.
  • Is the home or building being cleaned/dusted regularly? Some methods of dusting just throw the dust into the air, only to be captured by the air filter.
  • How many occupants are within your home or building?
  • What about air pollution in the neighborhood?

Pretty complicated and very different for every home or building. Therefore, no one can state a specific “time” period to clean or replace an air filter. Commercial and industrial HVAC systems may have had gauges installed which maintenance personnel must go to and read the system pressure to determine whether the air filter requires service, very time consuming, and time is money in the commercial and industrial space. An inconvenience for the household.


Until now! The FILTERSCAN WiFi Air Filter Monitor will notify you (and your maintenance technician if desired) when your air filter requires service, either via text or email, or both. 

Which does your furnace air filter look like?
Clean and Clogged Air Filters.JPG
Clean or Clogged?

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