What is an Allergy Filter and Other Questions about Allergy Filters

No matter what time of year it is, people are asking about allergy filters. In spring, summer and fall people folks are concerned about pollen. In fall and winter, people want an allergy filter to handle mold, dust mites, and pet allergens. Everyone wants an allergy filter, but they don’t understand what makes an allergy filter. What is an allergy filter? Are all allergy filters the same? Let’s answer these questions and other common questions people have about allergy filters.

allergy filter for petsWhat is an Allergy Filter?

An allergy filter is a filter, attached to a machine, that is designed to remove allergens from the air. All makes and models have a few things in common. They all have a motor that moves air to and through the filter as well as the actual filtering media itself. They do the same thing, but achieve various results.

Different filters remove different allergens. Some allergy filters aren’t even filters at all. Sound confusing? It can be difficult to compare allergy filters. So let’s break it down.

Allergen Particle Sizes

If you are shopping allergy filters, you already know the particles you want removed from the air. But do you know the size of those particles? That’s important.

freezing kills dust mites
Dust Mite Magnified

Dust Mites.  The allergens from dust mites range from 10 microns to 3 microns. Dust

mite bodies and body parts are at the top of the range (10 microns) and dust mite feces are at the bottom. All parts of the dust mite make you sick, but no dust mite allergen is visible. Whether you can see them or not,  you don’t want to breathe any dust mites or feces. Dust mite allergens can only be removed by HEPA filtration.

Molds. Mold spores are giants of the allergen world. These spores can range from 10 to 30 microns. Some mold spores are visible to the naked eye. That’s good news for air filtering. The larger the particle size, the easier it is to trap. Some dust masks act as wearable allergy filters. The Q-Mask and μ2 Mask stop mold. Many AC filters can capture mold as well.

fight ragweed allergy with masks and nasal irrigationPollen.  Pollen can be as small as 2 microns and as big as 750 microns. Most of the allergy-causing pollen can be seen unaided. It’s that white or yellow stuff you see on your car in the spring. Pollen can be captured by special window screens, masks, AC filters or HEPA filters.

Pet Allergen. Pet allergens are tricky. Technically, it is a protein in the saliva and urine that causes a problem. Dried saliva bits can be as small as 2 to 3 microns. Their jagged edges cause them to stick to just about everything. That makes them hard to filter. Fortunately, most pet allergen is attached to a bit of skin or fur (dander) that is much larger; making it easier to filter out.

Air Fresheners Toxic For Allergy Sufferes


VOCs and Gasses. Gasses must be filtered using a different process. The aerosol particles that hold the gas in suspension are so small that regular allergy filters won’t do the job. VOCs and gasses must be absorbed to remove them from the air.

 HEPA Filters

Most allergy filters contain some form of HEPA filtering media. So, what is a HEPA filter? HEPA is a measurement that means the filter removes 99.97% of particles as small as .3 microns. That’s really small! HEPA filters remove allergens from pets, dust mites, pollen, and mold. This type of allergy filter will capture bacteria, but not viruses.

In order for a HEPA filter to work, a motor must use a fan to pull air to the machine, through the filter, and back out into the room.

allergy filter to improve indoor air qualityEvaluating HEPA Filters.

To evaluate a HEPA filter, you need to look at:

  • the size of the motor
  • filtering capacity
  • the size of the room

The motor must be strong enough to move the air in the room. It must pull air from all around the room and through the filter. The filter should be large enough to hold a substantial load of particles. Because HEPA filters can’t be washed and they must be replaced, you want a filter that will serve you for an extended period of time. Changing filters frequently is time consuming

Thermodynamic Filters

These filters are often sold as allergy filters, but they don’t filter at all. They remove allergens from the air by moving air to the unit by convection (no fan) and then destroying the allergen with heat.  These machines are popular with people that are just as interested in ridding the air of bacteria and viruses as allergens. That’s because the same technology that lays waste to pet allergen also incinerates viruses and bacteria.

Evaluating Thermodynamic Filters

These units are mini crematories. They destroy with heat. Because they rely on  convection to move air, there are no motors or fans to evaluate. Focus on the incinerator.

  • How hot does it get?
  • Does it emit or produce ozone as a by-product?
  • Does the heating unit create light?

That final bullet is important if you put one of these units in a bedroom. If you need total darkness for sleep, any light might keep you awake.

Allergy  Filters for HVAC

If you have a furnace or central AC unit, you’ve got to keep a filter on the unit. The purpose of the filter is to keep the unit clean, not your house.  However, a quality filter on the furnace or AC will help keep dust and allergens from circulating in the house.

You must walk a fine line with high efficiency filters.  Air can’t get through the filter and be heated or cooled if the filter is too fine. It puts a strain on the blower motor. Too little filtration and you might as well not have any filter at all.

Evaluating HVAC Allergy Filters

Most important is the fit. Air follows the path of least resistance. If your filter doesn’t fit properly, air flows around it and not through it.

Use a MERV 8 filter. A filter with a lower MERV rating is okay if it is treated  with a tacking agent. The tacking agent makes the filter media sticky and increases efficiency.

multigas filter to improve indoor air qualityPicking an Allergy Filter

Now that we’ve answered the question, “What is an allergy filter”, you are probably asking yourself “what kind of filter do I need?”.

We can help!  Read “ How to Evaluate Allergy Filters” next!

Wishing you the best of health
Mike Krause


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