Answers to How Often You Should Change Your Furnace Filter

When it comes to maintaining a healthy central air system in your house, most homeowners are aware that they need to regularly change their AC air filters. However, they may not be aware that they also need to change their furnace filter at regular intervals.

All central air systems with a heating component have a “furnace.”

The furnace is part of your HVAC air filtration system responsible for taking cold air in and heating it up before it’s blown throughout the rest of the home through the air handler.

Furnaces - the heating component of your central air system - are made of several primary parts that are responsible for heating the air inside of your home. The heat exchanger, combustion chamber, and air blower help to condition the air. Your furnace filter helps to clean it.

So, how often should you really change your furnace filter? Let’s take a deeper look at your home’s furnace filter, what it does, and why it’s important to regularly change your furnace filters.

shop whole house custom furnace filters with Filterbuy

First, What Does a Furnace Filter Do?

Before we get into the details surrounding when and how often to change furnace filters, let’s discuss why they are needed in the first place.

The furnace filter is used to clear the air of contaminants and dust just before air is pulled into the furnace system. The air passes through the filter material where contaminants are trapped. This keeps contaminants out of the furnace and HVAC equipment that’s further down the line.

Without a filter the furnace would cease to operate rather quickly because the equipment would be too gunked up to operate properly.

There are also a couple residual benefits that come from using furnace filters. In addition to keeping the HVAC system clear of contaminants, furnace filters also help clean the indoor air that you breathe. All the air purification allows the HVAC system to run as efficiently as possible, which lowers the cost of heating and cooling a home. Learn more about different types of furnace filters.

Not All Central Air Systems Have a Furnace Filter

You may not have realized your furnace filter needs to be changed because furnace filters aren’t needed in every HVAC system. It all depends on the equipment that’s involved and how the system is designed. Below are a few instances when a HVAC system won’t need a furnace filter.

Central Air Systems Without a Heating Component

example of a central air handler without a heating component

Some people live in climates where air cooling is needed almost year-round, which means heating the house isn’t a concern. It’s possible for HVAC systems to have no heating component and therefore they don’t need a furnace filter.

HVACs With Single Air Filtration Systems

central air unit with a single filtration system

Some HVACs are designed to have a single air filtration system rather than a separate system for the air conditioner and furnace. When this is the case just a single HVAC air filter is needed. The filter is placed in a shared air handler where it cleans the air before it’s diverted to either the conditioning unit or furnace.

How Often to Replace & Change Your Furnace Filter

how often you should be replacing your furnace filter in your home

Your specific situation is unique, but most air filtration experts agree that there is a general lifespan for furnace filters.

The standard recommendation is to replace furnace filters at least once every 90 days.

Keep in mind, this is a general recommendation. There are a few factors that can shorten or extend the time between furnace filter replacement intervals.

Furnace Filter Thickness & Change Intervals

different sized thickness furnace filters

One of the biggest variables is the thickness of your furnace’s filter.

Furnace filters are typically 1-, 2-, 4- and 5-inches thick. The thicker a furnace filter is, the more it can hold and the longer it will last. Below is a quick reference for filter thickness and change intervals:

  • 1” furnace filters should be replaced every 1-3 months.
  • 2” furnace filters should be replaced every 1-3 months.
  • 4” furnace filters should be replaced every 6-9 months.
  • 5” furnace filters should be replaced every 9-12 months.

The thickness of your furnace filter is dictated by your air handler and furnace’s filter slot. You can’t try to cram a larger air filter in a small vent slot. It’s also not advised to use a furnace filter that is too thin for your furnace filter slot. That will result in inadequate filtration and contaminants making their way into the air in your home.

Also keep in mind that thicker furnace filters tend to last longer, providing more filtration over time, so they tend to cost more than 1” and 2” furnace filters.

Signs It's Time to Replace Your Furnace Filter

a dirty furnace filter is a good sign its time to replace

There are a lot of variables that influence how often a furnace filter needs to be changed. Plus, you may need to change the furnace filter more frequently at certain times of year. Instead of just going off the standard timeline, below are some signs and special considerations that will let you know when to change a furnace filter.

Symptoms of an Old or Dirty Furnace Filter

  • Increased heating bills and energy costs during colder months
  • Worsened air quality inside the house
  • Constant temperature fluctuation
  • The furnace shuts down due to clogs in the equipment
  • The heat exchanger is prematurely worn or damaged
  • The presence of dust and pet dander around the house
  • Increase in allergies or breathing issues or symptoms

When in doubt, just take a quick look at your furnace filter. When a filter has reached the end of its life it will appear very dirty. Instead of seeing white pleats, the air filter medium will be a darker color, often grey or brown. You may even see larger bits of debris.

Furnace Filter Change Intervals in Winter vs. Summer Months

Generally speaking, HVAC furnace filters don’t need to be changed as regularly during winter months compared to summer months. In the winter, as long as the furnace filter isn’t dirty and clogged, you can go the recommended 90 days before needing a replacement. But if you have higher-than-normal usage during a particularly cold period, it may warrant an earlier replacement interval.

It all comes down to a matter of runtime and humidity. Typically, the air conditioner runs more hours of the day in summertime. Longer runtimes mean that more air is passing through the filter each day. Higher humidity levels in the summer or winter can also make your furnace filter damp. The added moisture reduces the filter’s capacity to hold contaminants, and it will need to be changed more frequently.

What Could Happen If You Don’t Change Your Furnace Filter

Let’s look at worst case scenarios if you don’t change your furnace filter on time.

At this point you may be wondering how important changing your furnace filter is in the real world. You may even think you can skip a few changes if you live in a mild climate or aren’t worried about air quality in your home.

an old or dirty furnace filter can cause damage to your heating system

Even if you live in a temperate climate with great air quality, there’s another important reason to change your furnace filter as recommended. Clean furnace filters help protect your HVAC system.

The primary purpose of a furnace filter is not to clean the air you breathe but to clean the air that’s passing through the furnace and other HVAC equipment. There are hundreds of components that can be negatively impacted by air contaminants. When contaminants enter the system, they can cause build up and premature wear that makes the equipment work harder.

If you don’t regularly change your furnace filter, you can end up with a furnace that doesn’t operate as efficiently and will likely have a shortened lifespan. This ends up costing homeowners money in the short-term since more energy is used to heat and cool the home.

Long-term costs include more frequent repairs and needing to replace the furnace or entire HVAC system sooner than expected.

Shop Furnace Filters with Filterbuy

Looking for the best air filters for your home? At Filterbuy you can find specialty furnace filters and standard HVAC filters in a wide range of sizes and thicknesses. We can also create custom size furnace filters so you get an exact fit!

We also offer 5-inch furnace filters (16x25x5 or 20x25x5), whole house air filter brands, and rigid cell furnace filters.

Furnace Filter Changing FAQs

How often should you replace your furnace filter?

The general recommendation is that furnace filters should be replaced at least once every 90 days.

How long is a furnace filter good?

A furnace filter will last if the medium can collect airborne contaminants. Once the medium is fully saturated it will no longer be able to filter the air.

How often should you change a 1-inch furnace filter?

A 1-inch furnace filter should be changed at least once every 1 to 3 months or every 90 days.

How often should you change a 2-inch furnace filter?

A 2-inch furnace filter needs to be changed every 1-3 months.

How often should you change a 4-inch furnace filter?

A 4-inch furnace filter should be changed sometime between six and nine months.

How often should you change a 5-inch furnace filter?

You can wait 9 to 12 months before needing to replace a 5-in furnace filter.

How often should you change a furnace filter in winter months?

During the winter when the furnace is used more often, you will need to replace the furnace filter more frequently. It’s not uncommon for furnace filters to need to be replaced once a month in the winter. However, if your HVAC has a single filtration system that uses one air filter for the conditioning unit and furnace then replacements will be less frequent in the winter compared to the summer.

How often should you change a Honeywell furnace filter?

A Honeywell furnace filter is going to have the same filter replacement recommendations as standard filters. Just be careful not to confuse Honeywell furnace filters with their HEPA air filters for purifiers, which last much longer.

How often should you change a Carrier furnace filter?

A Carrier furnace filter has similar filter replacement recommendations. Carrier’s fiberglass furnace filters should be changed every 30 days. Their pleated furnace filters can last anywhere from 3 months up to a year.

How often should you change an Aprilaire furnace filter?

Aprilaire furnace filters tend to last a little longer than the norm. The manufacturer recommends changing their filters every 6 to 12 months.

How often should you change an Air Bear furnace filter?

Some Air Bear furnace filters can last six to nine months before needing to be replaced.