How Furnace Filters Help With Allergies – Removing Triggers

Furnaces with generic filters are largely ineffective at reducing airborne allergens. However, furnace air filters that are HEPA, pleated polyester, carbon, fiberglass or those with MERV rating >11 can remove common allergens, such as dust and pet dander, and may help with allergies.

Furnaces are an everyday appliance in cold areas and most modern ones come with air filters. So, it’s only natural to wonder if furnace filters can help with allergies by removing things like dust, pollen, and dander.

This article discusses common allergens, their occurrence, and their effects on health. We then dig into furnace filters and how efficiently they can remove airborne allergens.

Allergies and Allergens

Most people are familiar with the concept of an allergy, and know that it is a hypersensitivity reaction.

Our natural immune system helps protect against foreign bodies by initiating inflammation. However, if the immune system goes into overdrive, it leads to abnormal inflammatory reactions, destroying the body’s cells. This is the true definition of an allergy.

Common allergy symptoms include:

  • Runny nose
  • Sneezing
  • Facial pain
  • Headache
  • Breathlessness
  • Swollen eyes and mouth
  • Pain in throat

Depending on the severity of the reaction, the symptoms might resolve in a few days, or they may persist and worsen over a few hours.

Types Of Airborne Allergens

Here are the common types of allergens present in the air:

Particulate Matter

Amidst rising pollution, our air is increasingly becoming concentrated with particle contaminants, like:

  • Dust: It comprises fine earth particles or waste matter lying around the ground. Even though dust exposure is common because air is dense, some people are particularly sensitive to it.
  • Pollen: Pollens are yellowish, microscopic grains discharged from flowers. They are primarily concentrated in the air in the spring season.
  • Pet Hair and Dander: Pets shed hair and dead skin cells. They are allergens on their own and act as a carrier for dust and pollen.

Particulate allergens are especially hazardous for asthma patients.


Germs like mold, bacteria, and viruses are found in the air and can lead to multiple allergies.

  • Molds: They are microscopic, multicellular organisms that exist in the air as spores. These spores can trigger respiratory problems upon inhalation. They also release mycotoxin, a poisonous chemical that can cause allergies, cancers, renal failure, and other medical issues.
  • Bacteria: They are microscopic, unicellular organisms. While some bacteria are used in antiallergic medications, certain bacterial species cause allergic inflammation.
  • Viruses: Like bacteria, viruses are concentrated in the air. They are responsible for the transmission and development of various respiratory viral infections like pneumonia, cold, and flu.

Gases and VOCs

While pathogens and dust are usually considered allergens, airborne gases, chemicals, and volatile organic compounds (VOCs) can also trigger allergies.

These include carbon dioxide, carbon monoxide, nitrogen oxides, formaldehyde, etc.

While most of these allergens naturally occur in the air, some VOCs and gases like ozone, soot, smoke, exhaust fumes, etc., are emitted into the atmosphere from heating, construction, fire breakouts, or artificial production.

Plentiful Air has more information on VOCs and which air purifiers effectively remove them available here.

Furnace Filters and allergens

A furnace is clearly a device that heats cold air, and it does this by:

  • Pulling in cold air via a rotating fan that circulates it through the system.
  • The air is passed through a furnace filter, usually located at the side or floor of the device.
  • Inside a metal chamber, the filtered air is heated via combustion.
  • The warm air is then emitted into the room.
  • In condensing furnaces, the exhaust gases (from the metal chamber) are processed in a secondary heat exchanger for extraction of remaining heat. The cold gases condensate into water droplets which drip through the drain pipe.
  • The exhaust gases in conventional furnaces are directly emitted through the metal flue (instead of passing through the secondary heat exchanger).

Filters are used in furnaces because they protect the furnace and improve the air quality.

Protects The Furnace

Air contains various pollutants like dust, debris, pet hair, dander, germs, VOCs, dangerous and odorous gases, etc. If the filter doesn’t remove some of these from the circulating air, the pollutants can accumulate and build up inside the furnace.

It can lead to:

  • Formation of mold colonies which can then damage the furnace material
  • Obstruction of airflow due to collection of dust and debris
  • Clogging can block the pipe, preventing the condensate from draining out of the unit.
  • Obstruction due to particulate matter can also impair the airflow, which won’t only hamper the heating process, but also cause the furnace to overheat. The overheating may result in the formation of toxic by-products like carbon monoxide.

Improves Air Quality

Furnace filters improve the air quality. Airborne contaminants can cause health complications, such as severe allergic reactions, wheezing, chest pain, respiratory distress, etc.

By reducing the concentration of airborne pollutants, furnace filters improve the air quality, making the air safe to breathe.

Can Furnace Filters Help With Allergies?

There are three main factors that determine the filtration of allergens from a furnace:

1. Filter Type

Understandably, the type of filter factors in when it comes to allergen filtration.

There are various air filters, and each can remove a different type of contaminant depending on the filter pores and chemistry.

Whether a furnace can remove allergens or not depends on the type of filter installed in it.

Reusable Generic Filters

Some furnaces use a generic filter with large pores. This filter can only remove large-sized particles and has no effect on gases, germs, pollen, dander, etc.

Disposable Pleated Filters

Pleated and fiberglass filters are the most common furnace filters.

Pleated filters are synthetic filters made of polyester, cotton, or paper. As the name suggests, the material is molded into many folds (or pleats), increasing the filter’s surface area, allowing it to capture more pollutants.

They come in different sizes, but almost all of them can capture microscopic contaminants (0.2 – 0.4 microns), which include particles and pathogens. Their efficiency can range from 35 to 80% depending on the quality.

Disposable Fiberglass Filters

Fiberglass filters consist of spun glass encased in cardboard. Since the material is readily available, the filter is inexpensive and is used in many appliances, including furnaces.

They can primarily catch particles that are larger than 50 microns (like pollen grain and dust) but may also capture 20 to 25% of pathogens.

Electrostatic Filters

Some furnaces use electrostatic filters that emit high-energy charged particles (positive and negative ions). These particles produce static electricity inside the furnace, causing the airborne particulate matter (dust, debris, pollen, hair, dander, mold spores, etc.) to fall on and stick to the surrounding surfaces while the filtered air is pushed forward.

HEPA Filter

HEPA or High-Efficiency Particulate Air (HEPA) filters are one of the most efficient filtration systems. Theoretically, they can remove more than 99.97% of particles and pathogens (measuring 0.3 microns or more) from the air.

This implies that the filter can clear the air of many allergens.

Carbon Filter

Carbon or activated charcoal filters are created by heating and oxidizing pure carbon to make it highly porous.

They extract gases, VOCs, and chemicals from the air by adsorbing them on the filter surface and trapping them inside the pores.

Since the primary function of furnace filters is to protect the blower fan and other system components from particle buildup, carbon filters are not a common sight in furnaces.

To put it all together, all furnace filters (except the generic ones) can remove allergens. Still, the combination of carbon filters (for gas filtration) and HEPA filters (due to high efficiency) would be ideal for maximum protection against allergies.

If you are limited to one filter type then a HEPA filter will remove more of the common allergens (dust, pet dander and hair, pollen) than the carbon filter.

Note that all furnaces may not necessarily come with your preferred combination, but most modern models are compatible with different types of filters.

2. Merv Rating

Merv stands for ‘Minimum Efficiency Reporting Values. The rating scale ranges from 1 to 20, and determines a filter’s potential to capture fine particles, measuring between 0.3 to 10 microns (higher the number, higher the efficiency).

Besides the size of the filter pores, its thickness also defines the effectiveness. Thin filters would saturate frequently and won’t be able to remove allergens and other contaminants efficiently.

Theoretically, you should always look for a filter with the highest MERV rating. However, with increased filter thickness, there is a high chance of obstructed airflow (which can cause the appliance to malfunction).

MERV ratings of air filters and the percentage of particles removed in three size classes (0.3-1.0 micron, 1-3 micron and 3-10 micron)
Particle size efficiency of filters (in microns). Data sourced from the U.S. Environmental Protection Agency. Created by Theresa Orr.

A Merv rating of ~11 is considered ideal for allergen removal and optimal furnace operation.

3. Filter Size

Filter size is measured by its thickness, height, and length. The suitable filter size for each model is mentioned in the user manual of your furnace.

Installing the right size is essential to ensure maximum air purification. While larger filters won’t fit properly in the system, smaller sizes allow the air to move around and past them without filtration.

Best Furnace Filters

Here’s the list of the best furnace filters for allergen removal:

Aerostar Merv 13 Pleated Air Filter 

The Aerostar Merv 13 Pleated Air Filter is designed to remove lint, dust, mites, spores, pollen, dander, viruses, and bacteria. It is simple to install and cost-effective. Its pleated construct and electrostatic function offer the best protection against allergies.

Flanders/Precisionaire Fiberglass Furnace Filter

Flanders/Precisionaire’s Fiberglass Furnace Filter comes in a pack of 12. It is inexpensive and yet offers highly efficient air purification.

Nordic Pure Pleated Air Filter

Nordic’s Pure Pleated Air Filter has a Merv rating of 12, making it ideal for home furnaces.

FilterBuy 20x20x1 HVAC Air Filter

This FilterBuy 20x20x1 HVAC Air Filter is marked Merv 8. A pack contains at least 4 FilterBuy filters, which can be used in furnaces, and other HVAC appliances.

AAF International New Case 12x30x1 Fiberglass Air Filter

AAF International’s New Case 12x30x1 Fiberglass Air Filter has minimal airflow resistance and lasts up to 30 days. It can be installed for efficient air filtration in furnaces and ACs.

Can A Furnace Filter Make Allergies Worse?

High-quality furnace filters compatible with your model help protect you against allergies. However, when not cleaned or replaced regularly they can have adverse health effects.

Air filters have a specific capacity beyond which they cannot capture more pollutants. If not cleaned regularly, the filter pores become saturated.

Impaired Filtration

A clogged filter does not remove further contaminants allowing them to be emitted into the room with warm air.

Mold Build Up And Emission

The airborne pollutants escape the filter buildup inside the furnace. These contaminants include mold spores that thrive in high temperatures (between 70 to 90 degrees F).

Since a furnace is a heating system, its environment is naturally warm and facilitates mold growth. The mold spores produced are blown out of the system and can lead to allergies.

CO Production

Saturated air filters (or thick filters) obstruct the airflow, leading to carbon monoxide (CO) production.

Carbon monoxide is a toxic and potentially lethal gas produced from incomplete combustion. Usually, heating a fuel causes oxygenation of carbon, resulting in CO2. But inadequate airflow implies less oxygen supply, and insufficient oxygen causes the formation of CO.

This can also lead to allergy symptoms.

How To Maintain Furnace Filters To Prevent Allergies

Improperly maintained furnace filters pose a significant risk of allergen exposure. Here’s how you can clean and replace them to avoid such a problem:


  • Turn off the furnace, and disconnect it from the power supply.
  • Locate the furnace filter, and following the instructions on your user manual, gently remove it from the device.
  • Use a clean cloth to remove dust from the filter. If the manual doesn’t advise against using it, you may also use a handheld vacuum.
  • Rinse the filter with lightly running warm water. Again, sometimes water can damage the filter media, so check with the manual beforehand.
  • Let the filter dry before placing it back.


If you’re using a non-washable HEPA filter, a disposable filter, or your reusable filter is swollen and dirty even after rinsing, you need to replace it.

  • Before you start, make sure the furnace is off and unplugged.
  • Locate the old filter and remove it.
  • Take the replacement filter (which should be of the same size as mentioned on the old filter), and try to slide it in the slots. Ensure the arrow on the filter (which indicates the airflow direction) faces towards your furnace and away from the air duct.

Can A Dirty Furnace Filter Cause Allergies?

A dirty furnace filter allows mold and bacteria to build and multiply inside the furnace. These pathogens are then dispersed into the home, leading to allergies. Saturated filters also constrict air flow and might lead to carbon monoxide emission from the furnace.

How Often Should You Change A Furnace Filter?

The standard 4″ furnace filters need replacement every six months. However, depending upon the pollution, you may need to change your furnace filter more frequently.

Theresa Orr

Theresa Orr holds a PhD in Earth Science and specializes in determining past climates from rocks using geochemistry. Her passion for clean water, soil and air drives her to provide easy to understand information for everyone to read.

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