To perform an air test for mold, an inspector uses a special device to capture mold spores onto some sort of collection media. The inspector then analyzes the sample by seeing how many spores are present. The indoor air sample is usually compared to an outside control sample.
The effectiveness of air testing is somewhat debatable. As of 2015, there are no official guidelines for determining a safe or acceptable level of mold spores in the air. In most cases, mold is visible to the naked eye and air testing is unnecessary. It can be beneficial to make sure that remediation procedures are successful. It may also be helpful to detect large, hidden growths.
Homeowners who decide to get mold testing done should be present to see the inspection, since unethical inspectors sometimes artificially inflate the results by shaking out rugs or furniture. Independent inspectors are also usually best, since companies that also offer mold cleanup services may have conflicts of interest.
Homeowners should expect to pay for the testing and be wary of companies that offer free tests, since those companies usually make their money by selling cleanup services. Simple testing is also usually enough, although some companies may try to sell gimmicks or secondary tests.