How Often You Should Change Your Furnace Filter

Paige Bennett
Written by Paige Bennett
Updated September 15, 2022
Woman enjoys coffee fireside while sitting in a swinging chair
Photo: Alena Ozerova / Adobe Stock


  • Furnace filters usually need to be changed about every three months.

  • The filter type and thickness can impact how often you should replace it.

  • Household habits, from opening windows to smoking, can also shorten the filter lifespan.

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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. 

How to Determine When to Change Your Furnace Filter

How do you know how often to change a furnace filter? In general, you should change the furnace filter about every three months

But there are other factors to consider that could require you to change it more often, including:

  • Dirty filter: If the filter is visibly dirty or dusty, go ahead and replace it.

  • Dust everywhere: If you’re breaking out the duster more frequently, you may need to change your furnace filter more often.

  • Frequent running: When the HVAC is kicking on more often and running for longer, it may be a sign you need to replace it.

  • Unpleasant odors: If your furnace area smells weird or has a burning smell, an old filter could be one cause.

If you’re still unsure if it’s time to change the filter or suspect something else is wrong, consult an HVAC pro near you to help you determine the best course of action.

Factors That Affect Your Furnace Filter Replacement  Schedule

Now that you know generally how often to change your furnace filter, let’s look at factors that might increase or decrease frequency. 

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: Less thick and less effective at blocking particulates, you may need to replace these filters as often as monthly, depending on visual inspection. 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–$50.

  • HEPA filters: According to the United States Environmental Protection Agency, HEPA filters get rid of 99.97% of contaminants in your indoor air. This type of filter should be changed annually, and it costs between $20 and $100.

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.  


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 in air ducts 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 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. 

Smoking Indoors

Smoke will wear out a filter fast, especially if multiple people in the home are smoking. With one person smoking indoors, change the filter at least every 60 days. If multiple people in the household smoke, you’ll want to upgrade to a thicker filter and change it more frequently, about once per month for filters thinner than 2 inches or about every three months for thick filters of 5 to 6 inches.

Open Doors and Windows

Opening the doors and windows can feel like a breath of fresh air, but with that air comes the dust, pollen, and other contaminants from the outdoors. That means your furnace filter is working harder to filter out all that dust and debris. 

If you like to open your doors and windows often during warm seasons, you’ll need to replace thinner filters once per month and thicker filters at least every three months.

How Often Heater Fan Is Running

Depending on your personal preferences and your location, you may like to keep the heater fan running. If so, you’ll need to replace the furnace filter more often, about once every month. If you rarely leave the heater fan running, you can replace the filter around every 90 days or longer for thicker filters.

Why You Should Change Your Furnace Filter Regularly

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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 often 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. 

Maintain 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

With more dust in the clogged system, the furnace can overheat and even start a fire, or the motor can burn out from working hard to try to push the air through. 

Dirty filters can also cause the furnace to shut off from short cycling, which could leave you cold in the middle of winter. Call a local furnace tune-up company if you notice any issues or need maintenance or cleaning services.

How to Replace a Furnace Filter 

Replacing a furnace filter should only take a few minutes out of your day, so it’s an easy task to add to your calendar. You may want to consult the furnace manual for exact instructions for filter replacement, but in general, it just takes a few steps.

1. Turn Off the Furnace

Start by turning off the furnace to avoid burning or injuring yourself. The furnace power switch is usually positioned near the furnace itself and looks like a normal light switch. The switch could also be on the furnace itself. 

2. Locate and Remove the Filter

Look for the service panel where the filter is located. This is usually on the front of the furnace, and the filter should be behind the panel. If you can’t find it, consult the manual or look it up online for your furnace model.

Once you’ve located it, remove the screws on the filter cover or simply slide out the filter, as some furnaces may not have a cover over the filter. You may want to lay down a towel or place a trash can nearby, since moving the dirty filter could loosen some dust bunnies and make a mess.

3. Replace the Filter

Slide the new filter into place, and screw in the cover if needed. Replace the service panel, and then mark your calendar for when the next replacement is due.

If you need help keeping up with changing filters or cleaning your furnace, talk to a furnace maintenance pro in your area.

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