How often should you change furnace air filter

Filter Type

The biggest factor in how often you should change your filter is the type of filter you use. There are two main filter types to choose from: fiberglass air filters and pleated air filters. Both types are disposable, but there are some important differences between them.

Fiberglass air filters are the more affordable of the two but less efficient at capturing dust and particles in the air. They generally need to be changed every 30 days or less.

Pleated air filters are more expensive at the outset, but they are also more efficient at trapping particles and can last up to 90 days, depending on use.

When you purchase a new air filter, you’ll find the manufacturer's recommendations for the replacement schedule. This is a general guideline, and depending on the following factors, you may need to change it more often—or less often.

Tip: Some filter models offer a subscription service that delivers a new filter to your home on a regular schedule. Opt for an air filter subscription if you don't want to worry about remembering to buy a new one.

Home Size

Home size is an essential factor in determining the frequency of your filter changes. Large homes, for example, circulate larger amounts of air through the furnace or air conditioner. This means that the filter may get dirtier faster and require more frequent replacement. In smaller homes, the HVAC system has to move less air, which can mean less frequent air filter replacements.

Tip: Smaller homes may also have smaller appliances, like air conditioners with smaller air filters. In this case, the filter may need to be changed just as often as in a larger home.

Air Quality

The air quality outside can have a big impact on how often your air filter becomes dirty and needs to be changed. If you live in a big city, contaminants like smoke, dust and other debris will seep inside and clog your air filter at a much faster rate. Wildfire smoke also plays a big role in needing frequent filter replacements. After a stretch of smoky days with poor outdoor air quality, inspect your air filter to check if it needs replacing.

Pets

Many people love sharing their homes with pets, but our furry family members do have an impact on the air quality inside of our homes. They release pet hair and dander into the air, and they track in dirt, pollen, mold and other contaminants from outside. If you have one or more pets, check your air filter each month, and replace it when it’s dirty.

Allergies

If you have allergies, you can reduce your symptoms by using a high-quality air filter and adopting a more frequent replacement schedule. Excess dust, pet dander and other allergens floating around in your indoor air can make symptoms like coughing, sneezing and a runny nose even worse. To ensure that only clean air is leaving your HVAC system, change your air filter before it becomes clogged so you can breathe easier.

Season

The frequency of your air filter changes will likely depend on the change of the seasons. During the mild spring and fall, your HVAC system will be running less frequently, so your filter won't get as dirty as fast. But when the heating and cooling seasons kick in, the filter will trap more contaminants. 

During the mild seasons, when you’re not running the HVAC system, you likely keep your doors and windows open and spend more time outdoors. During these months, the contaminants in your home may actually increase, but your air filter isn’t trapping them. This may worsen your seasonal allergies. To improve air quality, turn the fan switch on the thermostat from the AUTO position to the ON position. The fan will cycle your home’s air through the filter without heating or cooling. If you choose to run your fan during spring and fall, your air filter will need replacement as usual.

Occupancy

Children are more sensitive than adults to indoor air pollutants like mold, dust mite debris, dander and pollen, so make your home an oasis by using quality air filters and replacing them before they become too clogged and dirty. If you have young kids in the home, it is a good idea to use high quality, pleated air filters and change them as frequently as every two months.

As a general rule of thumb, lower home occupancy extends an air filter's lifespan, while higher home occupancy decreases it. A vacation home that you only live in part-time, for example, will need far fewer filter changes than a large family home with numerous occupants. If you live alone with no pets and good surrounding outdoor air quality, the manufacturer's filter change recommendations will likely work well for you.

Visual Inspection

The only way to be sure about how often to change your air filter is to perform a visual inspection of the filter every month. After a few months, you’ll get an idea of how quickly it becomes dirty. You’ll need to re-evaluate if you get a new pet or if the outdoor air quality has been poor.

Tip: To inspect an air filter, hold it up to a light source. If the light doesn't pass through the filter, it’s clogged and needs to be changed.