ERMI Testing Vs. Air Samples

Very often we receive calls from very concerned people that need help determining if they need an Environmental Relative Moldiness Index (ERMI) test or not.  The range of knowledge in the general public for this type of test varies.  In this post, I will highlight a few points to keep in mind when deciding on doing an ERMI test.First, let me provide some information per the Environmental Protection Agency’s (EPA) website on ERMI testing.  ERMI stands for Environmental Relative Moldiness Index.  The analysis from this test can be used by researchers to estimate the levels and types of mold inside a property.  The test is done by collecting a dust sample.  Since mold spores can settle onto dust, the DNA from the mold in the dust can be identified, thereby providing information on what types of mold are present.  However (and this is highlighted in bold lettering on the EPA website), “the ERMI should be used only for research.  The ERMI has not been validated for routine public use in homes, schools, or other buildings.”  The EPA also recommends that water damage is assessed during the inspection since moisture issues are what cause most mold problems.  

Our company performs several types of mold tests including ERMI and air samples.   Air samples differ from ERMI because no settled dust is used.  Instead, air is drawn through a cassette and any spores present are deposited onto a glass slide in the cassette and ultimately viewed through a microscope.  The laboratory analysis can tell us the concentration of mold that was found in the air along with the types of mold (generally, down to the genus level).  

So the main difference is that ERMI collects spores and DNA from dust, whereas air samples collect spores from the air.  What’s the big difference?  The spores settled in the dust provide more historical information and air samples provide more current information.  Is one better?  Not really, they are just different.  Analysis between the two types is another main difference with ERMI detecting DNA via polymerase chain reaction and most air samples being analyzed via the microscope.

ERMI tests use a statistical formula to provide a single ERMI number.  Interpreting that ERMI number can be a big challenge.

When potential clients ask us to perform an ERMI test, we first recommend that we do a visual inspection and moisture evaluation.  We recommend that they also do more traditional spore trap testing alongside ERMI.  This way we can provide them with both historical and current information regarding the mold levels in their home.   

This blog article is just scratching the surface about ERMI.  Please leave a comment if you have any questions.

EPA Website:

3 thoughts on “ERMI Testing Vs. Air Samples”

  1. We don’t know what to do. We suspected mold in our home, and heard good things about the ERMI test, so we did the test and the ERMI score was off the charts at 28.06. We brought in a home inspector, and found a concentrated problem area, got it fixed, then vacuumed (HEPA filter attached) the whole house from ceiling to floor, and followed that by spraying a 50/50 mix of hydrogen peroxide and vinegar. We let the house sit for 2 weeks (we temporarily moved out), and then retested; this time with both an Air Sample and an ERMI. The Air Sample showed a moderate level of Penicillium/Aspergillus fungal growth inside the home (none was detected outside) at 350 spores/m3. We cleaned some more, and started to move back in the home. Then, we got the ERMI results back last night. The results were super high again, at 22. What should we do? One test tells us to move back in, while the other tells us to move out for good. Ha! Seriously though, we are confused. Any suggestions on how to find clarity with our situation? Thanks for any tips.

    1. Jen,

      I emailed him directly with a response but I will post below what I sent him in case it is helpful for you or other people.

      Thank you for commenting Jen!


      An ERMI result is difficult to interpret that is why the EPA currently uses it as a research tool and not as a means to determine if there is a mold problem in a home. Whenever a client requests an ERMI test we also recommend getting air sampling done through a spore trap in order to get a better picture.

      Every situation is unique inside a home and the amount of mold in it can vary depending on the situation. Without doing an inspection and our own sampling it is difficult to tell you definitively what the mold issues in your home are. With that said, I can tell you that an air sample result of 350 spores/m3 of Aspergillus/Penicillium is not usually considered elevated. It is true that the outdoor control sample is the comparison that is used to determine if a particular mold level inside the home is high. However, in the midwest, for example, it is common for outdoor Aspergillus/Penicillium mold to be above 1,000 spores/m3 during the warmer months. Also, Aspergillus/Penicillium mold is not considered toxigenic (keep in mind that people are different and any mold at any level can affect each person differently depending on their individual sensitivities – like an allergy).

      Also, remember that mold is EVERYWHERE and it would be a nearly impossible task to 100% eliminate it from the air.

      If you still have concerns and you’re in the Chicagoland area consider having us do a mold inspection of your home.


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