How Often Should You Change Your Furnace Filter?

Changing the air filter in your furnace is a critical task that you must do to maintain its efficiency and longevity.

Some folks go without changing their air filter for months at a time—but they end up paying for it in the long run! Failure to change your air filter on a regular basis will bring increased energy and maintenance costs.

You should change your furnace air filter at least once every 3 months. If you have pets or a dusty home, then you should change your air filter at least once every 1 to 2 months.

These are general recommendations for filter change intervals—certain factors can extend or shorten your air filter’s lifespan.

In this article, I’ll discuss the factors that affect your air filter’s longevity. I’ll also go over how to know when it’s time to change your furnace filter.

Factors that affect how often you need to change your air filter

Even if you change your air filter on a strict schedule, you may need to change it sooner (or later) depending on the conditions inside your home.

Here are some factors that affect how often you need to change your furnace air filter:

  • The thickness of the air filter. Thicker air filters don’t need to be changed as often as thinner ones.

  • How often you run your furnace. If you only run your furnace for a few hours per day, then you won’t need to change your air filter as often.

  • How clean your home is. If your home is dusty or dirty, then you will need to change your furnace filter more often.

  • Pets in your home. Pets add to the dirtiness of a home, so you’ll need to change your air filter more often if you have them.

  • The number of people in your home. More people living in your home will make your furnace filter dirty quicker. More dust and dirt will get kicked into the air and trapped in your furnace filter.

  • The time of the year. Different seasons bring different pollutants into your home. For example, the spring brings pollen, so most people will need to change their filters more often during the spring.

What are some signs you need to change your furnace’s air filter?

Most people change their furnace filter on a strict schedule. But there are other ways to tell that your furnace filter needs changing.

Here are some signs that you need to change your furnace’s air filter:

  • Your home is dustier than normal.
  • Your furnace is running longer or more often than normal.
  • Your home isn’t reaching your desired temperature.
  • There are burning smells coming from your air vents or furnace.
  • Your furnace’s air filter is visibly dirty.
  • Your furnace is noisier than normal.

If you’re unsure if your furnace filter needs to be changed, turn off your furnace and take a look at the filter. When an air filter is excessively dirty, it will look brown or grey in color instead of white. If your filter is excessively dirty, then it’s time to replace it.

Visual comparison of dirty versus clean air filters
Visual comparison of dirty versus clean air filters

What happens if you don’t change your furnace’s air filter?

Failing to change your furnace’s air filter will cause all kinds of problems in your home.

Here is what will happen if you don’t change your furnace’s air filter:

  • Your furnace will have to work harder due to reduced airflow. A clogged air filter will constrain airflow through your furnace. Your furnace will have longer runtimes and worse efficiency.

  • You will have higher energy bills. Your furnace will need to consume more electricity and gas to heat your home, leading to higher utility bills.

  • Your furnace will experience more wear and tear. The increased runtimes brought on by a clogged air filter will cause your furnace to wear down prematurely.

  • Your furnace may shut down unexpectedly. A clogged air filter can cause your furnace to trip one of its limit switches. When your furnace trips its one of its limit switches, it will shut down.

  • Your furnace won’t keep a stable climate in your home. The lack of airflow from a clogged air filter will make it harder for your furnace to keep a stable temperature in your home.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

4 thoughts on “How Often Should You Change Your Furnace Filter?”

  1. New homeowners, mid-20’s, who are sending you our appreciation for your straight-forward, interesting and informative articles. You saved us money because we were told to get the highest MERV rating filters (just us, no pets.) We learned a lot and hope others will be so lucky.

  2. Im remodeling a condo thats 40 years old,I have contacted three supposedly ac pros, they said the ac that I have doesnt need a return, its in the bottom of air handler,I explained it should be in the hallway ,and duct work should be bigger, ready for this, they said it doesn’t need more air to be sucked in the air in the handler is adequate,I said see you lateral I right??

    • Hi Phil,

      It’s hard for me to tell without seeing the whole picture. Air returns don’t always need to be in the hallway as long as there is a clear path to the return.

      Perhaps it’s time to get a different company to give a second opinion.


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