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  • Gordon McIver

When or how often should I replace my air filter?

Is there a sure fire way to determine when to replace your furnace air filter? Short answer is "nope" because it depends on several factors. One thing is for sure, though -- a clean air filter will improve your indoor air quality, so don't forget. Or, call us for regular maintenance.



This is probably the question that I am asked most frequently by homeowners and the correct answer is: It depends. Another correct answer is: When it’s dirty.


The fact is that everyone’s home situation is unique and the frequency of air filter changes depends on a number of factors.


The “run time” of the furnace blower. The more hours that a furnace blower runs, the more frequently the air filter will need to be changed. If, for instance, the furnace is idle during the summer months then the air filter will not be loading up with airborne particles and will not need to be changed. But if you are using the furnace blower all year (as you would with both heating and cooling) then you will be changing out an air filter on a more regular basis.


The type of activity is going on in your home. Air filters collect airborne particles. A home with one or two occupants only will not generate anywhere near the amount of airborne particles you would get from five occupants with one or more pets. The more activity and foot traffic a home has, the more frequently the air filter will need to be replaced. An unoccupied home (or an infrequently occupied home) will not need much in the way of filter maintenance at all.


The type of activity going on outside of your home. In general, a home on a paved road will require less frequent air filter changes than a home on an unpaved road. Another source of trouble for air filters would be smoke particles from a forest fire in the area…sometimes from many, many miles away.


The type of air filter that you use. The more restrictive an air filter is (that is, the smaller particles that it is designed to trap), the more frequently it will need to be changed. Highly restrictive air filters are great at trapping tiny particles but they become clogged faster.

The location of your return air grill. A return air grill that is located near the floor will pick up airborne particles at a much faster rate than one located near the ceiling.


It may take some time to determine what your unique air filter replacement schedule is but once you know you can and should set it up as an event on your calendar so that it gets done. A clogged air filter is a source of trouble for any forced air system and I will explain why in another post.


For more information on air cleaners and air filters:


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