A furnace filter is an essential but sometimes overlooked component of your home heating system. It prevents dust, dirt, and other airborne particles from clogging your HVAC system while also improving your home’s air quality. The furnace filter needs routine replacement to remove these particles and debris. In general, you should change it every 2–3 months or whenever it looks dirty, but we’ll outline several factors that affect how often you should change your furnace filter.

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How Often Should You Change Your Furnace Filter?

Over time, particles become trapped in the furnace filter, restricting airflow through your heating system. This forces the furnace to work harder, which can result in a higher heating bill and eventually shorten the furnace’s life.

Check the manufacturer’s recommendations on how often to change your furnace filter, but the typical suggestion is every 60–90 days. This also depends on your system’s age and how often it’s used. The EPA suggests checking your filter once per month, especially during winter, and changing it if it looks dirty. Change the furnace filter every three months at a minimum.

If you have a HEPA (high-efficiency particulate air) filter, you may be able to replace it less often than a fiberglass filter, and some are even washable. This type of air filter removes at least 99.97% of dust, pollen, mold, bacteria, and other airborne particles with a size of 0.3 microns. HEPA air filters require replacement once per year.

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Filter Types and Costs

• According to Angi, a simple fiberglass filter costs around $5 but won’t do much to clean finer particles out of the air.
• Polyester and pleated filters cost around $30–$50 each and do a better job removing contaminants.
• A HEPA filter costs between $20 and $100, depending on the manufacturer and MERV rating, but will remove 99.97% of contaminants.

Review your air-filter options in the video below with This Old House plumbing and heating expert Richard Trethewey.

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What Does a Furnace Filter Do?

A furnace filter protects your home from dust, hair, debris, and other contaminants that come in through your HVAC system’s return duct. Without a filter, debris and other particles will collect in your heating system, which could affect your furnace’s energy efficiency. The furnace filter also improves your home’s indoor air quality by removing potential irritants and allergens from the air. This is especially important for anyone with allergies or asthma.

A higher MERV rating means the filter is better at trapping these particles, but it will need to be changed more frequently than a filter with a lower MERV rating. The most common type of filter is a disposable pleated furnace filter, but there are several options with different MERV ratings. Most residential furnace filters have a MERV rating of 7–12, but anything 13 or over is considered a high-efficiency filter. Most modern furnaces are compatible with high-efficiency filters, but if you have concerns, speak to an HVAC technician.

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Reasons To Change Your Furnace Filter More Often

The following factors also affect how often to change a furnace filter.

• Pets: There’s one big drawback to having furry pets in the house: dander and fur. If your cat or dog sheds a large amount of fur, you may need to check your filter more frequently than the minimum recommendation. You can reduce the amount of pet hair and dander clogging your filter by regularly cleaning and grooming your pet.
• Allergies and asthma: A high-efficiency air filter can reduce the number of allergens in the air, such as pollen, pet dander, dust mites, and mold spores. Consider a HEPA filter with a MERV rating of at least 13 to help relieve allergies and asthma. Be sure to change the filter more frequently if you experience these issues, especially during pollen season.
• Indoor air quality: Air pollution is one of the world’s biggest environmental health risks, and indoor air is two to five times more polluted than outdoor air. Change your air filter more often if you’re concerned about your home’s indoor air quality or if the air quality has diminished.
• Dust: Small particles like dust can irritate your allergies or trigger an asthma attack. Most dust particles are 5 microns or less in size and only HEPA filtration is efficient at removing them from the air.

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DIY vs. Professional Furnace Filter Cleaning

Most homeowners can handle basic furnace filter replacement. However, you should schedule annual preseason check-ups with an HVAC contractor, ideally in spring and fall. Unless you have the skills and training necessary to clean the other internal components of a furnace, that part of maintenance should be left to a professional. 

A technician will inspect and clean the system’s components to ensure your furnace runs efficiently. Duct cleaning isn’t considered part of yearly maintenance, but it may improve your home’s indoor air quality if done every few years.

Professional Furnace Cleaning

A professional furnace cleaning typically costs between $60 and $400, with an average cost of about $150. Electric and gas furnaces cost about the same to clean, but oil furnaces are more expensive. Here are some of the specific tasks involved in furnace cleaning:

• Inspecting the vent system and air intake for blockages
• Cleaning the blower and checking the motor
• Lubricating all moving parts
• Cleaning the combustion chamber
• Inspecting the flue pipe
• Testing component efficiency
• Replacing the oil filter
• Checking the air filter and replacing it if necessary

Regular furnace cleaning performed by a professional improves the system’s performance, safety, and longevity. You can also catch problems early, like a crack in the heat exchanger that only a trained technician might notice. This may save you money in the long run.

DIY Furnace Cleaning

Do-it-yourself (DIY) furnace cleaning saves you money, though you’ll have to pay for the new furnace filter and cleaning supplies—thorough furnace cleaning consists of more than just changing the filter. We recommend consulting a professional, but here are the basic steps to DIY furnace cleaning:

• Turn off the system: Begin by turning off the electrical power and fuel supply. Locate the red power switchplate at the top of the basement stairs or near the burner. The fuel shutoff valve is near the oil tank or on the incoming gas pipe.
• Clean the combustion chamber: Use a small wire brush and an industrial shop vacuum to clean soot from the chamber.
• Inspect the flue pipe: Look for holes in the exhaust flue that could leak carbon monoxide. While small holes can be patched with foil tape, corroded flues must be replaced.
• Replace the oil filter: If you have an oil-powered system, close the oil valve and remove the old filter.
• Change the air filter: Remove the existing filter, located just inside the furnace or inside the air return vent. Make note of the filter size listed on the frame so you’ll know what size to buy.
• Clear the blower of debris: Lift the blower compartment door and vacuum inside.
• Clean the floor vents: Remove floor registers and vacuum out the ducts

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Our Conclusion

A clean furnace improves your home’s indoor air quality and increases your heating system’s performance and lifespan. You can replace a furnace filter on your own, but routine maintenance should be performed by a skilled technician. Furnace cleaning can be complex and potentially dangerous, especially if you’re unfamiliar with the necessary equipment and safety procedures.

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FAQ About Changing Your Furnace Filter

What happens if I don’t change my furnace filter?

If you don’t change your furnace filter, the filter can become clogged so that little air passes through. A clogged filter can damage your HVAC system and allow contaminants to circulate through your home.

Do furnace filters really last three months?

Most air filter manufacturers say to replace the furnace filter every 90 days. However, this depends on other factors, such as your home’s location, if you have allergies or respiratory issues, and your system’s age. You may need to replace it more frequently.

How often should you change your furnace filter in winter?

The general rule for how often to change a furnace filter is every 2–3 months, but because you use your furnace more during winter, it can become dirty quickly and should be checked more frequently.

What are the symptoms of a dirty furnace filter?

The most common symptoms of a dirty furnace filter are higher heating bills, poor air quality, and bad airflow. You may also notice uneven heating from one room to the next or a burning smell when your furnace kicks on. 

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