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What You Need to Know About Changing Furnace Filters

Is your home dusty and are allergy symptoms getting worse because of your furnace? Yes, this is possible if the furnace filter hasn’t been changed in a while. The filter is designed to trap dust and many other airborne particulates (including pollen and mold spores). Here’s what you need to know about changing furnace filters so your heater performs reliably and efficiently.

When Should I Change the Furnace Filter?

The time interval for changing a furnace filter depends on a few factors. You may need to replace the filter every month or every year. This all depends on:

The Size of Your Household

Larger households typically require the furnace filter to be changed more frequently because there are more people to introduce more contaminants.

HVAC Usage

The more your heating system is operated, the greater the volume of air that circulates through the filter. Therefore, it can become dirty and clogged more quickly.

Indoor Air Quality Issues

Poor indoor air quality can cause the filter to clog up faster. Filters can last longer in cleaner air, and if air purifiers and air cleaners are installed.

You Have Pets

Pet fur and dander contribute to particulates that are picked up and caught by the furnace filter. This can shorten its useful life by about 30 days.

Allergies or Asthma

If anyone in your household has allergies or respiratory issues, even a tiny amount of particulates can cause symptoms, so changing furnace filters should be a more frequent task.

Filter size also influences how often you change it. Follow these general guidelines for replacing furnace filters based on their thickness:

  • 1 to 2 Inches: Replace every 1 to 3 months.
  • 3 to 4 inches: Replace every 6 to 9 months.
  • 5 to 6 inches: Replace every 9 to 12 months.

Also, check the manufacturer’s suggestions as to when to change your furnace filter.

Types of Furnace Filters

There are a few options available. The least expensive, disposable fiberglass filters are usually contained in a cardboard frame. They typically last about one to two months. Disposable pleated paper filters are designed to remove even smaller particles. Depending on the product, it can last from four months to a year. Reusable electrostatic filters trap even tinier particles, including those found in smoke. They often have a plastic frame and can be easily sprayed clean with a garden hose.

Some furnace filters can trap microorganisms like mold, fungus, algae, yeast, and bacteria. They’re rated as high-efficiency particulate air (HEPA) or antimicrobial filters.

Changing a Furnace Filter

Installing a furnace filter is similar to putting in a new air conditioner filter. First, identify the type and size of filter that’s required for your heater. Once you’ve purchased the right filter, follow these simple steps:

  • Turn off the furnace to avoid contamination, damage, or potential injury.
  • Locate the furnace filter, which is often located near the ductwork or blower fan.
  • Find the unit’s service panel and remove it.
  • Once you find the existing filter, slide it out.
  • Find the arrow on the new filter showing the proper airflow direction (it must point toward the furnace and away from the return duct).
  • Position the filter accordingly and slide it in.
  • Switch the furnace back on.

It’s also a good idea to write down the date you changed the filter. This will provide a reminder and a reference as to when to change it again. You can also schedule reminders and alarms using your smartphone’s calendar app.

What Happens If You Don’t Change the Filter

Changing furnace filters is simple. But many people neglect it, which can result in a variety of problems. After all, the filter not only protects air quality but also your HVAC equipment. Failing to change it can cause:


  • Damage to vital, yet sensitive, components due to dirt and debris.
  • Poor HVAC performance due to blocked airflow.
  • The unit overheats and shuts down.
  • An increase in energy consumption as the furnace requires more power to move air.
  • Short cycling, leading to wear and total system failure.
  • A clogged condensate drain, an overflow, water damage, and higher humidity.
  • Poor heating and inconsistent heating from room to room. 

Changing a furnace filter as required helps the unit provide more reliable heating, run more efficiently, and can prevent major repairs and delay system replacement.


Contact Hays Cooling, Heating & Plumbing

Hays is a leading provider of heating services in Phoenix, AZ. When your furnace isn’t operating as efficiently or providing enough heat, our qualified heating repair technicians can diagnose and fix it right the first time. We’ll help find the right solution that fits within your budget. To request assistance, schedule service online or call 602-932-7275 now.

About the Author

Chris Hays

Founder of Hays Cooling, Heating & Plumbing

Chris and Stacia Hays, are the founders of Hays Cooling, Heating & Plumbing; a family operated HVAC company in Phoenix founded in 2001 that services both commercial and residential customers. Chris leads a team of certified technicians who have over 45 years of combined experience and has earned and A+ rating with the BBB and a strong five star rating online. Hays Cooling, Heating & Plumbing focuses on providing support to their customers every step of the way, with exceptional service and competitive prices. If you are looking for top-notch air conditioning and heating service, contact Hays today.