Quick answer: No single mold test gives a complete picture of your home. Air samples, surface samples (tape lifts and swabs), dust-based DNA tests like ERMI and HERTSMI, and particle counters each show part of the story. A good mold investigation combines the right tests with a visual inspection, moisture readings and a look at your HVAC system.

“What’s the best way to test for mold?” We hear it all the time. The honest answer: no single method gives a perfect snapshot of your home’s “mold load” at any given moment. Each kind of test has its own strengths and blind spots, and if you don’t know them going in, the results can confuse more than they help.

Here’s where each common method shines and where it falls short. One thing to know first: in Texas, mold testing is a job for a licensed mold assessor, and state rules bar one company from both assessing and remediating the same project.

What are the common mold testing methods?

What does an air sample show? (Spore trap and viable sampling)

A spore trap shows which mold spores were floating in one spot during a few minutes. Think of it as a fishing net. A small cassette attached to a pump pulls in air, usually at 15 liters per minute for 5 minutes, for a total of 75 liters. That’s a thimbleful compared with the air in a whole house, and it only counts spores that happen to be airborne at that exact moment.

The catch? Mold isn’t always releasing spores. It cycles between growing, resting and sporing, and when it’s “happy” (say, on a bathroom wall with steady moisture) it may release few spores while you test.

That’s how a wall with visible mold can still produce a “clean” spore trap: the mold simply wasn’t sporing at the time.

Spore traps are non-viable samples: a lab identifies the spores under a microscope, living or dead. Viable air samples use a different sampler that lands spores on growth plates, and the lab counts what grows. Either way, you get a snapshot of airborne spores in a short window, in a single spot.

What is a tape lift test?

Exactly what it sounds like: clear sticky tape is pressed against a suspicious spot (that fuzzy patch near the toilet base, or the odd stain on a window sill) and sent to a lab, which identifies whether it’s mold and what type.

It’s great for settling arguments like “Is that mold or just dirt?” But it won’t tell you how much mold is in your home overall, and results are often reported on a general 1-to-4 scale. A “4” just means “there’s a lot of it right here,” which says nothing about whether your HVAC system is quietly moving spores through the whole house.

Do petri dish “home test kits” work?

Not really. Inexpensive DIY petri dish kits tell you very little. Mold spores are everywhere outdoors, and they naturally drift inside. Set a petri dish out in your living room and something will almost certainly grow.

That doesn’t mean your home has a problem. It means you live on planet Earth. These kits can’t tell you whether your levels are normal or high, and they can’t point to a source. Plenty of homeowners have panicked over a fuzzy dish that only caught normal background mold.

What is a swab test?

It’s a cousin of the tape lift: a sterile swab is rubbed across the surface and sent to the lab. Depending on how the lab analyzes it, a swab can be cultured to show whether viable (living) mold is present, which a standard tape lift can’t do. That makes swabs handy in certain cases, like checking whether a recent cleaning did its job. But they still only tell you what’s on that one surface, not what’s in your air or behind the walls.

What is Andersen sampling (cascade impactors)?

It’s the “old-school” way to take a viable air sample. Air is pulled through a stack of metal plates with progressively smaller holes, which sorts particles by size onto culture plates that a lab then grows out.

In theory, that tells you more than a standard spore trap, because you learn particle size as well as type. In practice, it’s bulky and slow, and the equipment must be cleaned carefully between sites so it doesn’t carry contamination from one test to the next. And like the other air-based tests, it only measures what’s airborne in a small space during a short window.

What are ERMI and HERTSMI tests?

They’re the DNA tests of the mold world. ERMI (Environmental Relative Moldiness Index) and its scaled-down cousin HERTSMI-2 start with dust collected from a defined area, usually by vacuuming or wiping a set section of floor. The lab then uses DNA analysis to identify specific mold species and estimate how much of each is present.

The big advantage: ERMI can hint at your home’s mold history, because dust hangs on to spores and fragments for a long time. That makes it valuable for understanding past water damage. The downsides: it’s one of the pricier tests, and it can pick up “old” DNA that may not reflect current conditions. It’s a strong tool for a baseline, but less useful for checking whether recent remediation “worked” in the short term.

Can a particle counter detect mold?

Not specifically. Particle counters use laser light to measure the number and size of particles in the air in real time. Because most mold spores fall within a certain size range, a trained technician can make educated guesses about whether mold may be part of the particle load.

The good news: results are immediate, which helps during an inspection, for example to find which room or supply vent has higher counts. The bad news: high counts could come from anything (dust, pollen, pet dander, last night’s fajitas), not just mold. And if the mold isn’t actively releasing spores, a particle counter won’t catch it.

So which mold test should you use?

Usually a combination, because no single test tells the whole story and every method has blind spots. A thorough mold investigation pairs the right tests with a careful visual inspection, moisture mapping and (most important) an understanding of your home’s history and HVAC system. In Texas, when a mold remediation project is above the size threshold in the state rules, a licensed mold assessor handles the formal assessment and post-remediation evaluation under the Texas Mold Assessment and Remediation Rules.

Found mold in your AC system or ductwork? Call Gold Eagle Services, a licensed Texas mold remediation company that handles HVAC mold. Mold in walls, attics or belongings goes to a general mold remediation company.

Know what each test can (and can’t) tell you before you spend the money. Sometimes the best next step isn’t another test at all. It’s tracking down moisture sources, checking your humidity control and fixing the conditions that let mold grow in the first place. In humid Central Texas, that often starts with the AC system, the attic ductwork and the drain line.

What should you do next?

Write down what you’ve noticed: visible growth, musty smells, past leaks or water stains.
Check your indoor humidity and look at the AC drain line, two common moisture sources here.
Skip DIY petri dish kits, since they can’t tell you whether your levels are normal.
Book a visit to have the AC system, attic ductwork and drain line checked for moisture problems.

About Gold Eagle Services: This guide comes from the team at Gold Eagle Services, a family-run Austin HVAC, indoor air quality and mold remediation company founded in 2017. We’re licensed (TACLA119235 and RCO1783), insured and bonded, and we serve homes across the greater Austin area.

Need help with this in your home? Learn about our HVAC mold treatment and remediation, or call 512-489-4653 to schedule a visit.

Related Gold Eagle service: HVAC mold remediation

Mold Testing: What Each Method Can and Can’t Tell You