How To Test For Mold In A Home - Air Sampling or Dust Sampling?

By: Licensed Mold Assessor Brad Fishbein

January 4, 2023

If you want to know how to test for mold but don't want to hire a professional, you can do the testing yourself.

However, just to be clear...

Mold testing and a mold inspection are two separate things.

A mold inspection should always be done by a professional, but mold testing is a process that can be on your own if you would like.


What Is Mold Testing?

Mold testing involves the collection of samples commonly via air, culture, bulk, dust and surface. The sampling medium is then analyzed by a microbiologist to determine the amount of mold spores and what specific species of mold is present in the tested areas.

Sampling does not necessarily need to be completed by a licensed professional if the sampling is being completed for yourself in your own home (check with your state regulations to confirm).

But what kind of sampling should you be doing?

You can do a variety of different type of testing. Some of the testing is intended to determine mold directly on materials which include a swab or tape lift sample to test for mold.

Then you have other types of mold sampling more intended to determine how the air quality is affected.

The two most common forms of sampling to determine if your air quality is affected is air sampling and dust sampling.

So, let's explore them both.

Air Sampling For Mold- How Does It Work?

Air sampling for mold is used to determine the amount of mold spores in the air. A negative air pump collects a sample of air over a short-term period (2,5 or 10 minutes). Mold spores are collected on a sticky substance in the middle of the cassette and then counted under a microscope. Lab results from an accredited third-party laboratory will determine both the raw spore count and the m3 (per cubic meter) readings of the air sample.

Air samples can be a great tool in determining if there is a mold problem that is affecting the air quality.


How To Take Air Samples For Mold

  1. Set up an air sampling pump on a tripod 4-5 feet from the ground (or lower, see next section)
  2. Install a cassette with the stickers removed to expose the sticky substance on the calibrated pump
  3. Press the button to start the pump for 2, 5, or 10 minutes
  4. Seal the sticky substance back with the stickers and label the cassettes
  5. Send to a laboratory for analysis


There are debates about the conditions of the home while sampling. I will break down the norms of what most professionals do, and then I will break down what the contrarian says on what the conditions should be when air sampling.

Common Theory #1- Sampling should be completed with the pump on a tripod.

Most professional organizations including the American Industrial Hygiene Association (AIHA) recommends have your sampling pump 4-5 feet off the ground.

Contrarian Theory #1- The pump should be taken at ground level so it can collect mold from the dust particles on the ground and have a true idea of what is floating around the home.

My Commentary

I understand the theory to try and collect mold spores and fragments that may be deep in the pores of the carpet and won't show up in an air sample.

But why not just take a dust sample if that's the case?

An air sample taken on a tripod represents the airborne spore count floating around the air at that particular time which is what the purpose of the air sample is.

In a perfect world, taking samples both ways would be ideal. But budget comes into play as it costs money to analyze mold samples by a microbiology lab.

Common Theory #2- To test for mold, air sampling should be done in a controlled building environment meaning with no people in the room, doors closed, ceiling fans off.

Contrarian Theory #2- Air sampling should be done with building activity including people sitting on couches, walking on carpet, etc.

My Commentary

It really depends on what the air sampling is looking to accomplish. If you are trying to establish if there are high amounts of airborne mold spores in a certain section of the home, the doors should be shut with no building activity besides the HVAC running.

If you wanted to establish baselines throughout the home then you would want building activity throughout.

For example, if you have kids running around normally, have kids run around during sampling.

However, the contrarian's point is to have people step on carpets, sit on couches, lay on beds etc., to determine if there are mold fragments and spores in the furniture and carpet.

The question again is why not just take a dust sample?

Pros Of Air Sampling

  • Can provide an accurate representation of how much mold is present in the air at any given time
  • Can possibly indicate an area where hidden mold growth may be present
  • Sampling can be done in a short period of time
  • Species of mold can be identified under a microscope
  • Spore counts can be compared to the exterior to determine if the spores originated within the sampled area

Cons Of Air Sampling

  • Only indicates how much mold is present at the time of the sampling
  • It's possible to get false-negative/positive results based upon the activity occurring within the building
  • May not include pick up mold fragments in settled dust
  • Cannot determine if the mold spores are active or dormant
  • Can be quite pricey if done by a mold professional
  • Most microbiology labs won't tell you if there is clusters of mold spores together on the sample which can indicate it's from a mold colony
  • Can't tell the exact strand of the species of mold (some families of mold have many different strands)

Is Air Sampling For Mold Worth It?

Air samples are basically just that…

Samples of air.

The samples are only ran for a short period of time and only represent the conditions that are present at the time that the sample is taken.

There are certainly flaws if using air sampling as your only tool when determining if there is a mold problem within the home.


What Is Dust Sampling To Test For Mold?

Dust sampling for mold involves obtaining a collection of dust (approximately the size of at least a nickel's worth) and sent to a laboratory to determine how much mold and what species of mold is present. Dust samples can give a more accurate portrayal of past mold damage as opposed to active mold problems.

Dust sampling is an excellent way to determine if there are settled mold spores in the dust around the home.

You may be thinking:

If dust samples only really detect past mold problems, then what's the point?


Here's why it matters according to the EPA (Environmental Protection Agency):

"Mold does not have to be alive to cause an allergic reaction. Dead or alive, mold growth can cause allergic reactions in some people."


To elaborate even further, dead mold may even harm people more than living mold. The reason is living mold needs water to survive.

When mold is wet, the spores are heavier and may not become airborne as easier. When they are dead, the spores aren't as heavy and can become aerosolized with much more ease.

Is all dust sampling created equal?

No, they are actually two popular ways to test dust for mold.

One is which is outlined above by looking at the dust under a microscope and another way that has become more popular over the past 15 or so years is called ERMI testing.

What Is ERMI Testing?

ERMI (Environmental Relative Moldiness Index) testing for mold growth is a PCR-based analysis that checks for a list of specific strands of the species of mold and assigns a spore equivalent level. ERMI will detect lower quantities of mold because the detection limit is lower than traditional dust sampling.

Instead of looking under a microscope, the DNA of a handful of different mold species are checked for.

ERMI sampling tests for the most common types of mold in homes that can cause mycotoxins.

How To Collect Dust Samples

  1. Collect approximately a nickel's worth (approximately that for ERMI) of dust with a sampling cassette to vacuum the surface.
  2. Place the dust sample in a sandwich bag and seal it.
  3. Send to a laboratory for analysis

Note: Some laboratories will give you a swab and tell you to swipe on building materials throughout the home instead of a large cluster of dust


Not all laboratories will perform ERMI testing so you have to find one that does it. Most will sub the samples out even if they don't analyze themselves.

Pros Of ERMI Testing

  • Can determine if there are mold spores and fragments found in settled dust
  • Results assign a spore equivalent level
  • Smaller fragments may be identified than in traditional dust analysis
  • Will not be impacted as much by background debris
  • Can aid in the discovery of possible past mold problems within the building

Cons Of ERMI Testing

  • Only searches for a certain mold species
  • Results are sometimes hard to interpret for the everyday person
  • ERMI testing can be very expensive (approx. $300-500)
  • There is no indication if the dust is aerosolized
  • ERMI testing alone cannot indicate if the spores originated in the home or were brought in from an outside source

Air Sampling Vs. ERMI Testing

Air sampling will give a clearer indication of the current mold conditions within the building by determining how much mold is present in the air and what kind of mold growth.

ERMI sampling presents a picture of historical data in regard if there were past mold problems in the building by analyzing the amount and species of mold in the settled dust.

But which one is better?

The answer is one isn't necessarily better than the other. They serve different functions.

Both of them can be used during a mold investigation if the budget allows it.

That being said, there is one thing that is more important than any kind of sampling…

A visual and moisture assessment.

Determining if there is or has been any water damage in a home is crucial. Examining your air conditioning and ductwork is also very important.

Both air sampling and ERMI sampling to test for mold can actually be done by a non-professional if they have the equipment and then sent to a third-party laboratory for analysis.

However, by doing that you will skip the knowledge and expertise of the mold professional.

Nevertheless, air sampling and/or ERMI testing is a good place to start when determining if you have a mold growth problem in the home.

Meet the author: Brad Fishbein is an ACAC council-certified Microbial Investigator. In the fall of 2012, he became a Licensed Mold Assessor in the State of Florida through the Department of Business & Professional Regulation. Brad has helped homeowners with over 5,000 successfully completed Mold Inspections since 2009.

Find a Mold Specialist Now

Click or Call, Toll-Free 24/7