How Often Should You Replace Your Furnace Filter?

  1. Dirty furnace filter

Changing your HVAC system’s air filter is a basic part of maintenance that every homeowner needs to make a priority. When heating and cooling systems run on dirty furnace filters, energy efficiency and comfort suffer, and your equipment suffers damage. How often should you replace furnace filter units? Mission Mechanical shares when air filters should be replaced and what can impact the lifespan of a filter.

How Often Should You Change Furnace Filters?

The frequency in which you should replace your furnace’s air filter depends on a number of factors. The filter manufacturer’s instructions will list the recommended frequency for filter changes, but this suggestion isn’t necessarily correct for every system.

The manufacturer’s recommendation serves as a good starting point. This is a general estimate based on the type of filter in use. While filters can require replacement once per month to once every year, depending on the type, the following is a guideline you can utilize to determine minimum frequency for changing the filter in your HVAC system.

  • 1- to 2-inch filters: Replace every one to three months
  • 3- to 4-inch filters: Replace every six to nine months
  • 5- to 6-inch filters: Replace every nine months to one year

Factors Affecting Filter Life

There are many factors that can decrease the life of a furnace filter, including:

Household Size

The number of people in your household will impact how often you should change your furnace filter. Larger households typically see more airborne contaminants than homes with fewer people, as people track in and introduce a variety of pollutants. 


Many animals will add pollutants to your home environment. If you have pets that shed fur and dander, your furnace filters are going to fill up at a faster rate than filters in homes without animals. Hair and dander are easily picked up as air circulates through living areas and are tracked through your HVAC system. Each furry pet in your household can reduce the lifespan of your furnace filter by one month, so be sure to keep this in mind when determining how often to replace furnace filters.

Indoor Air Quality Equipment

Do you have indoor air quality (IAQ) products installed that are working with your HVAC system to address airborne pollution in the home? Air cleaners and air purification systems that use filtration provide advanced filtration for the HVAC system and are highly efficient for the removal of many airborne contaminants. With these types of filters in use, your standard furnace filter is likely to last longer, as the job of pollutant removal isn’t left to this filter alone.

HVAC System Use

How often your heating and cooling systems cycle will impact air filter life, too. Systems that cycle frequently to maintain higher indoor temperatures during the winter pass air through the filter more often than systems that don’t operate as often. During times of the year when your HVAC system is in heavy use, expect that the filter won’t last as long as it does during times when outdoor temperatures feel mild.

Keep an Eye on Your Filter

Knowing when to replace furnace filters isn’t an exact science. Schedules are different for every household and can vary throughout the year. Because so many factors can impact the longevity of your filter, it’s best to inspect the filter’s condition on a regular basis.

We recommend taking a look at your furnace filter at least once per month. Check its surface area and see if there is free space left or if the entire surface is covered in matter. If the filter has no free space left, go ahead and replace it right away with a new filter, no matter if your typical schedule says your system isn’t due for a change. With eyes on your filter each month, you can assess if the filter life is on track with your estimates or if a fresh filter is needed sooner than usual. Your system won’t be left to operate months on end with a dirty filter in place, and you can keep your heating and cooling equipment running at peak efficiency throughout the year.

Heating and Cooling Maintenance from Mission Mechanical

Regularly replacing furnace filters is critical to a homeowner’s HVAC system maintenance routine. Professional maintenance tune ups should be, too! Mission Mechanical offers heating and cooling system maintenance tune ups to keep your HVAC equipment in top condition throughout the year. Contact us today to request service.

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