HVAC mold remediation is the removal and treatment of mold growing inside ductwork or on HVAC components. It's a restoration job with a defined scope — containment, physical removal, and sometimes encapsulation to protect cleaned surfaces — not a can of antimicrobial fog.
The most important rule is sequencing and proof. The EPA's guidance is that you should clean (remove the source) before any treatment, and that a suspected mold problem should be confirmed by a laboratory rather than diagnosed on sight. Sanitizing a system that doesn't have a documented problem offers little benefit.
This is the most over-sold corner of the duct business: '$99 inspection' visits that 'find' mold and pivot to a thousand-dollar treatment are common. A legitimate remediator holds IICRC or NADCA VSMR credentials, tests before treating, and gives you a written scope you can verify.