Cleaning coils, blowers and ducts; chemicals in HVAC systems

In plain English

Once the system has been assessed and any mechanical fixes made, cleaning follows the NADCA ACR standard. If the Condition of the system is unclear, an IEP with HVAC training should assess it. Cooling coils deeper than about four rows are hard to clean all the way through. One check is to compare the pressure drop or airflow across the coil before and after cleaning. Coils that cannot be cleaned should be replaced. Blower wheels fouled with growth lose much of their airflow and may need replacing if they are pitted.

Coil cleaners can damage fins, and any residue left behind gets blown into the house, so thorough rinsing is required. Using the HVAC system to help dehumidify during a job is possible, but R520 lists factors to weigh first, including pressurization, fresh-air intake, spreading particles through ducts, and decontaminating the system afterward. Containment is usually not needed for duct cleaning, except in sensitive settings or where the air handler sits in living space.

Antimicrobials, sealants and coatings inside ductwork are a last step, never a substitute for removing growth. They must be EPA-registered specifically for HVAC use, used exactly per label, and meet fire-safety testing required by NFPA 90A/90B. Verification by an IEP should happen before any coating is applied. R520 adds that the owner should be told what a coating will and will not do before it goes on, and that fire-test documentation should be obtained from the manufacturer first. If a label cannot be followed in full, including its protective equipment, the product should not be used.

Key points

• Clean to NADCA ACR; replace coils and blowers that cannot be cleaned.
• Rinse coil cleaners off completely.
• Think through the risks before using the HVAC system to dry a house.
• HVAC chemicals must be EPA-registered for that use and applied per label.
• Verify cleanliness before any duct coating or sealant goes on.

Official text

This topic is covered in our own words because the standard behind it is copyrighted; we cite it below rather than reproduce it.

Citations

• IICRC S520 Reference Guide, IICRC S520 Standard and Reference Guide for Professional Mold Remediation — Reference Guide — Ch. 12, pp. 131–133. Best practice

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