How Often To Change Furnace Filter?

We’ve all turned on the furnace after the fall has started winding down only to smell that musty, hot smell that really says, “I haven’t been switched on in months!” A good bit of that mustiness comes from dust buildup on and in your furnace. One solution to this issue is replacing your furnace filter regularly – but how often does “regularly” mean? 

Furnace filters need to be changed roughly every 90 days. Factors that affect how often you need to change your filter include the kind of filter you use, how many people live in your home, whether you have pets, and how often you use your furnace.

Some filters can last for longer than others, so you’ll need to know what kind of filter you have before you can know for sure how often you need to change it. Let’s take a look at why replacing your furnace filter is important and how often you need to do so. 

Understanding the Function of a Furnace Filter

Most people mistakenly believe the furnace filter works to keep dust out of the air so it won’t settle on our furniture or find its way into our lungs and sinuses. While filters do keep dust out of those and other places, that’s actually a side effect of them doing their actual job, which is to keep dust and other particles and debris out of your HVAC system.

We’ve already reminisced about that “smell of winter” we get when we kick the furnace on for the first time each year. That’s due to dust buildup in the ducts and on the furnace. But when the furnace pulls air in, heats it, then pushes it back out into your home, it takes in more than just air. 

All those dust motes and other floaties you see in your house, especially when you look in a beam of sunlight streaming in the window – that’s all dust, and since it floats in the air, it’ll eventually get sucked into the furnace. Build enough of it up in there, and you’ll have some problems beyond that musty almost-burning smell at the start of the season.

Filters catch that dust and all the other floaters and stop them before they can get in and gum up the works of your furnace. It’s almost an unintended consequence that the air coming out of your ductwork has less dust in it than the air that went in. That translates to less dust on your shelves, among other places.

Read: Does Furnace Filter Size Matter?

When To Change Your Furnace Filter

The simplest answer is that you should change your furnace filter once every 90 days. However, that’s an average, and there are several factors that affect how often you’ll actually need to make the change. These include:

The Number of People Living in the Home

Up to a quarter of dust particles are dead skin cells. Since dead skin cells constitute so much of the dust in our home, it’s pretty obvious that more people will create more dust.

Dust also consists of pollen, soil, and other particles from outside. If several people are living in one home, it stands to reason there’ll be more trips from outside to inside than in a single-person home. This results in more outdoor air contaminants getting into the house and needing to be pulled out of the air with the furnace filter.

The more populated your home, the more often you’ll need to change your filter. For example, a conservative estimate would say that The Brady Bunch probably needed to change their filters at least every 45 days— six kids, three adults, and all that long, blond hair? Those filters were working hard.

Whether You Have Pets in the Home

Cats drop dander pretty much everywhere they go, as do dogs and guinea pigs. Dogs and cats shed year-round, even though most of us think it’s just a warm-weather thing. The fact is that even after they’ve acquired or lost their winter coats, pets still lose hair just like people do because that’s how hair works.

Additionally, if you have a litter box in your house, you’ll have the dust from it getting stirred up along with the regular, non-pet-related dust already in your home. Pets create more pollutants, and if they’re indoor-outdoor animals, they’ll bring stuff into your home. 

Keeping pet dander, hair, and other pet sheddings out of your furnace requires a filter that gets changed at least every 60 days, and if you have more than one pet, you may need to change it out every month (30 days).

Read: Why Furnace Is Running But Not Blowing Air?

How Often You Use Your Furnace

The more you use your furnace, the more stuff will get trapped in its filters. So, if you live in a part of the country where you don’t need to run your furnace every night of the winter, you can cut back on your filter-changing schedule.

Even if you run your furnace daily, you can cut down on how often it runs by using something like the Google Nest Smart Thermostat (available on Amazon.com). Smart thermostats like this one allow you to program your HVAC system to take a rest while you’re at work or otherwise out of the house. If you’re at the office for eight hours, your furnace doesn’t need to work for all eight of those hours and keep your home at a toasty 74 degrees.

Program your thermostat to turn on the heat an hour or so before you plan to get home. It won’t run throughout the day, which means fewer contaminants got pulled into the filter.

Read: Cheap Vs. Expensive Furnace Filters

Recognizing When Your Filter Needs Changing

You’ve already planned to change your filter every 90 days. However, if the discussion above makes you feel you’ll need to change your filter more often, make sure you schedule time to check on the status of the filter a bit more frequently. The first few times you change your filter will give you a better idea of what your schedule should be like going forward, and you can stop paying as much attention. 

A good way to know that you’ve left the filter in for too long is if you’re met with a hail of dust when you attempt to change it. If this is the case, you’ll need to change it faster in the future. 

Start by checking your filter monthly. If you see dust has built up on your filter, it’s time to change it. A dirty filter will have a grey cast to it, and tapping it’ll cause some dust to puff up from it. These are clear indicators to change that filter.

Less obvious clues that your filter needs changing include noticing more dust than usual building up on your furniture and around your home and that your heater seems to run constantly. If it can’t get the air it needs because the filter is full and blocking air intake, the furnace will have to work longer and harder.

Read: Why Does My Furnace Filter Get Dirty So Quickly

Kinds of Filters

There are three main types of furnace filters available for you to choose from. 

The most common option is a disposable fiberglass filter such as the AAF Flanders Air Filter (available on Amazon.com). This kind is the one that nearly everyone has seen before. These filters are (as the name implies) disposable and are a cost-effective option.

Pleated filters are a bit higher-end and filter out smaller particles than fiberglass filters. Additionally, they also last a little longer, and some manufacturers say their filters can last up to a year. You’ll need to check the filter regularly before deciding on the frequency with which you change it. If you’re looking for a pleated filter, a good option is the Filterbuy Pleated Furnace Filters (available on Amazon.com).

At the top of the furnace filter hierarchy are reusable electrostatic filters. Aside from trapping dust, they can also filter out smaller particles, including smoke. The best part about them is that you can rinse them off and reuse them once they’ve gotten good and dust-laden. However, it should be noted that they are also the most expensive of the three. 

If you’re looking for an electrostatic filter, one good option is the AirCare Furnace Filter (available on Amazon.com). This filter comes with a lifetime warranty, and the company claims you’ll never need to buy another filter. Even without such a warranty, if you take good care of your electrostatic filter, it should last you for years.

Read: Does Furnace Filter Affect Air Conditioning?

Conclusion

Changing your furnace filters regularly will help your furnace run cleaner and more efficiently, and you’ll also notice less dust in your home once you have a clean filter in place. In general, you should change your filter once every 90 days

However, check the filter more often for the first few months – different homes put different strains on their HVAC systems, and you may need to change your filter on a different schedule. That said, houses with pets and smokers will need a filter change much more often than every 90 days to guarantee good performance from the furnace.