How Often to Change a Furnace Filter: Everything You Need to Know

Everybody loves a warm home, especially during the winter. Furnaces serve the very purpose of keeping your home warm and, like every other piece of equipment, require maintenance now and then. So how can you tell when it’s time to change your furnace filter?

You should change your furnace filter at least every three months. Marking your calendar every three months may be confusing, so an easier way to remember is to replace it at the beginning of every season. Replacing may vary depending on how often you use your furnace.

The rest of this article will provide detailed information on furnace filters, including the importance of changing them, how to tell if they are dirty, and factors that affect how often you need to change your filter. Keep reading to learn more.

What Factors Influence How Often You Need to Change Your Furnace Filter?

Some factors significantly impact how often you need to change your filter. These include:

  • The number of occupants: Large households change their filters more frequently than small households because there tends to be more contaminants and congestion in the air with large numbers.
  • Whether pets live in the house: Pets also hugely contribute to contaminants in the home because they shed fur, which is picked up by the filters. Households with pets need to change filters more often.
  • The occupants’ allergies: If members of your home suffer from respiratory sickness or allergies, it is essential to change the filters frequently to keep the air clean and avoid illness and discomfort.
  • The season: We use our furnaces more often during winter and summer than in spring and fall. It becomes clogged faster in these months; hence you will change them more often during these seasons.
  • The home’s size: A larger home means more work for the furnace. Therefore, larger homes may have to change their filters more often than smaller homes.
  • The home’s air quality: Air quality depends on the appliances in your household. If you own an air cleaner, your filters won’t need to be changed as often because it reduces contamination compared to homes without air cleaners, where the furnace filters do all the work.
  • The filter type: The type of filter you use is essential. Fiberglass filters are changed more often compared to pleated filters and HEPA filters. Fiberglass filters are cheaper but require changing very often.

What Are the Different Types of Furnace Filters?

There are many different types of furnace filters. Fiberglass, pleated, electrostatic, and HEPA filters are the most common types one may find in a furnace. It is essential to know which kind of filter is compatible with your furnace before replacing it.

Fiberglass filters are very affordable; however, cheap can be expensive. They are the least effective when purifying air, especially fine particles. Hence, the air is not completely clean. They are also flimsy, hence the need to replace them more often than the others. It is advisable to replace your fiberglass filters every 30 days not to compromise your indoor air quality.

Pleated filters are made of polyester material which helps to trap fine particles. The more pleats a filter has, the more efficient it is in cleaning the air. It also has high resistance to airflow. They are a good improvement from the fiberglass filters and are inexpensive. They are also washable using soap and water. However, it is still advisable to replace them every 90 days or at the end of every season.

Electrostatic filters trap particles using electrostatic charges. They can also be reused by washing after removing the filter, which is good for the environment. However, you must ensure it completely dries before returning it to avoid mold growth. It is advisable to wash your electrostatic filter every one to two months depending on use.

HEPA stands for High-Efficiency Particulate Air. They are the most expensive and effective filters and eliminate almost 100% of particles by diffusion, direct impaction, and sieving. These filters are highly recommended for big homes and are commercially used. You may only replace your HEPA filters twice annually. However, buildings with high furnace use may replace their HEPA filters every 3 months.

What Is the Importance of Changing Your Furnace Filter?

It is essential to change your furnace filters because it ensures your system works efficiently; dirty filters are bad for your health. It also reduces maintenance costs, increases your system’s lifespan, and generally keeps your house cleaner.

An efficient system uses less energy, which reduces your electricity bills. If you don’t change your filters often, they get clogged up with dust and dirt. Clogging pushes the furnace to put in twice the effort to do a decent job using more energy. Changing the filters is cheaper and more effective.

Poorly maintained filters lead to respiratory illnesses such as asthma and allergies. Filters trap dust and other particles. If not changed often, their efficiency reduces, which reduces the quality of air in your home. A dusty environment can be very irritating. Clogging also makes it hard to maintain comfort levels.

A clogged furnace has to work twice as hard, increasing maintenance costs. It generates a lot of heat, causing it to overheat and short cycle. (Short cycling is when the furnace goes off before reaching the desired temperature and back up again.)  At that point, your furnace must be repaired, which is costly. It can also reduce the furnace’s lifespan by leading to complete failure.

A clean filter keeps your home cleaner. Dirty filters allow dust and other particles into your home, leaving your surfaces dirty and needing to be constantly cleaned.

How Can You Tell if Your Furnace Filter Needs Changing?

You can tell if your filter is dirty and needs cleaning or replacing by watching out for some of these signs:

  • The filter is a different color. You may notice some discoloration because of the dirt. If it is covered in dust and webs, you should know it’s time to get a new filter.
  • Your energy bills are higher. Dirty filters clog your furnace, causing them to work twice as hard, increasing your bills.
  • You start to fall sick more often. You may notice house members getting headaches, itchy eyes, and allergies caused by air congestion because the filter lets in dust and other allergens.
  • The furnace may start producing less heat. It may fail to warm your home as fast as it used to or take longer to reach a specific temperature. The main reason is that dirt and dust interfere with the system.
  • Your home becomes dusty, and you find yourself cleaning more often. This means your furnace has accumulated so much dust that it can no longer trap it efficiently; hence it circulates the dust back into your house.
  • The smell of something burning is a sign that your furnace is overheating. This smell arises when the filter is clogged, and the furnace has to work twice as hard to build heat.

Factors to Consider When Choosing a Furnace Filter

Choosing the right filter for your furnace depends on these three factors: size, type of filter, and MERV ratings. The factors are discussed in detail below:

Choosing Furnace Filters Based on Size

Filters come in different sizes. You have to find one that fits perfectly. You can measure the dimensions using a tape measure or find accurate measurements in the furnace manual. You can also check the existing filter where they are sometimes displayed on the surface.

Choosing Furnace Filters Based on Use

First, you must ensure you purchase filters for residential use, not commercial ones. There are many types of filters. You want to find one that traps contaminants effectively. There are disposable filters, washable filters, adjustable filters for substandard openings, and electrostatic filters that use static energy. For large households or homes with pets, you may opt to go for high-quality filters.

Choosing Furnace Filters Based on MERV Rating

A MERV rating measures how well a filter filters air particles; the ratings range from one to 16. Most residential systems have ratings of up to 12; beyond that are for commercial use. The higher the MERV, the better the system is at trapping particles. However, it does not speak on efficiency because there’s still the aspect of airflow.


You should change furnace filters every three months or every season. However, some factors such as home occupancy, pets, and allergies may require one to change them more often. Always check your filters to know if they’re dirty and look for signs like dirty surfaces, less heat being produced, and high energy bills that indicate the need to change your filters.

It would be best to be careful when picking out replacement filters by looking out for measurements and what purpose they serve. Change them often to keep your home clean and have clean airflow.