A Guide to How Often You Should Change Your Furnace Filter

Becca Stokes
Written by Becca Stokes
Updated November 16, 2021
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Not many homeowners mark their calendars for their next furnace filter replacement, but it’s an essential step to keeping your heating and cooling system in top form. Regularly replacing your furnace filter will help your HVAC system last longer, but knowing when to change it can be confusing. Let’s break down the basics of your furnace filter and nail down exactly how often you should be changing it. 

What Does a Furnace Filter Do?

Your furnace’s air filter keeps debris in the air (like dust and other contaminants) from getting inside your heating and cooling system. Though furnace filters are not designed to improve air quality, it’s a happy accident that many of the things the filter prevents from getting into your HVAC system also improves the air quality inside your home.

How to Determine When to Change Your Furnace Filter

Many different variables impact when you should change your furnace filter. But, a good rule of thumb is to look at the filter to help you decide. If it’s very, very dirty, with visible hanks of dust bunnies, it’s time to replace it.

When consulting an HVAC pro, you will likely hear some version of this: Change your furnace filter every 90 days (or every three months). But you may need to change it earlier depending on the type of filter you have and the other variables listed below.

Factors That Affect Your Filter-Changing Schedule

Filter Type

Furnace filters aren’t one size fits all. There are two different types of furnace filters, and the one in your furnace will determine how often it needs to be changed. 

  • Pleated Filters: Pleated filters are thicker than flat filters. Pleated filters last up to four months, but they are more expensive than their flat counterparts. Expect to spend an average of $50 on this type of filter.

  • Flat Filters: Flat filters are less expensive than pleated filters, but they don’t last as long, which means they need to be replaced more often than their pleated counterparts. Since they are less thick and less effective at blocking particulates, sometimes these filters need to be replaced as often as monthly, depending on visual inspection. Thankfully, they are relatively inexpensive. Expect to spend about $5 to replace a flat filter.

  • Washable Filters: This type of filter requires a different type of maintenance. Instead of regularly removing and replacing these filters, you simply wash them once a month and return them to their slot. This option costs between $30 and $50.

  • HEPA Filters: If you have people with allergies in your home, a HEPA filter is a good option because, according to the EPA, it gets rid of 99.7% of contaminants in your indoor air. This type of filter should be changed annually, and it costs between $20 and $100.


If you have an allergy to dust or pet dander, you should change your air filters more regularly than every 90 days. Try replacing your filters at 60 days, and if your allergies are still acting up, consider replacing your filters every month or upgrading to pleated filters.

Depending on the severity of your allergies, you may still have to change pleated filters monthly. But pleated filters will do a better job at keeping the air free from pollutants that might send you off sneezing.


If you have pets, you may want to change your furnace filters more regularly, too. This replacement schedule can double when the weather turns hot, and all those pets start to shed. A clean filter, be it pleated or flat, is necessary to keep the pet dander to a minimum. If you have pets, consider changing your furnace filter every two months. 

Home Size

Your home’s size can also play a pivotal role in how often you need to change your furnace filter. If you live in a larger house, that means that there’s a lot more air moving through the home and your furnace filter. 

To that end, people with larger homes may find, through trial and error, that they need to replace their filters more frequently than people living in smaller homes. Additionally, if your home smells musty, changing the furnace filter is one way to help the inside of your home smell great, too. 

Filter Thickness

The thickness of the filter you have in place also affects how often you should replace it. Thinner filters, such as the traditional disposable model (1 inch in thickness) should be replaced at least every two months. Thicker filters are designed to be more efficient because the thicker the material, the more debris it can filter out of your home’s air ducts. Even thick filters should be replaced every 6 to 12 months.  

Why You Should Change Your Furnace Filter

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Still looking for a reason to commit to replacing your furnace filter regularly? Here are two key examples of how switching out your furnace filter will help you in the long run.

Financial Savings

According to the U.S. Department of Energy, replacing your dirty furnace filters can reduce your utility bills by 5 to 15%. Not only does that free up funds in your monthly budget, but regularly replacing your filters can extend the life of your HVAC system. Since a new HVAC and furnace system costs an average of $5,500, it’s worth keeping it in prime condition. 

Furnace Health

When your furnace filter is dirty, air can’t move through it. Dirty furnace filters cause a lot of strain on your HVAC system and can lead to the need for major repairs, which can cost up to $2,000

DIY Furnace Filter Replacement

Thankfully, this is a task that most homeowners can do themselves. To replace your furnace filter, locate where it is held. Usually, it’s located directly on the front or the side of the furnace unit, but consult your manual if you can’t find it. 

Once you’ve located your filter, the next step is to remove the screws that keep the cover on top of the filter in place. Some systems might not have screws at all. In this case, slide them out of the slot where they are held. Remember, this filter is old and dirty, so be ready to catch the mess with a trash can. After that, it’s as easy as putting in the new filter and screwing on the cover (if needed). The final step is to set yourself a reminder for the next furnace filter replacement. 

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