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How often you should change your air filter will depend on several variables.

The size of your air filter

There are many different sizes when it comes to HVAC air filters. The last number in the size will tell you the thickness of the filter. For example, a 20x25x4 air filter is roughly 4 inches thick and normally lasts 6 months to 1 year. A filter that is 1 inch thick will need to be changed every 1 to 3 months. 

Time of the year

The HVAC system will run the most in midsummer and the middle of winter when heating and air conditioning are needed the most. In the spring and fall when the weather is nice the system will not need to cycle as often.


A family of 4 with a pet will need to change their AC air filter more often than empty nesters with no pets. 

MERV rating

A MERV rating is given to every HVAC air filter. The higher the number the more efficient the filter is. This means it stops more dirt and dust and smaller particles. The high the MERV rating the more often the filter will need to be changed. Be careful. Do not use a filter with a filter that is too efficient. For example, if you used a piece of cardboard for your air filter it would be considered 100% efficient because it stops everything. You want a filter that will clean the air and allow air through. This way the HVAC equipment can still function properly. 8 to 11 MERV-rated filters work well for most homes. 

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