HVAC
Mold in the HVAC system: how the S520 says to handle it
In plain English
HVAC systems can be a source of mold, a pathway that spreads it through the house, and a place it builds up and hurts the system's performance. So the S520 says the HVAC serving a moldy space should be part of the inspection and preliminary determination, checked for Condition 2 or 3, and returned to Condition 1 as part of the job. If there's growth in the system, the cause should be found and fixed, with repairs or modifications by a qualified HVAC professional and to code. Duct liner, duct board and flex duct with growth that can't be cleaned should be removed and replaced.
When HVAC cleaning is part of the job, the system should be inspected to the industry standards: IICRC S590, NADCA ACR and ACCA Standard 6. Those cover cleaning well but say less about mold assessment and verification, so the S520 fills the gaps and should be followed where mold remediation is needed. Building cavities used as plenums aren't covered by NADCA or ACCA and are handled like the rest of the structure.
The remediator should find out whether the system ran while mold was growing. A clean system that isn't the source should be isolated and protected during the work; one with only Condition 2 needs containment for the whole project. A contaminated system should stay off until it's cleaned, repaired and its moldy porous parts replaced, and if parts of it can't be contained the whole system should be shut off and contained. The S520 says the HVAC should not be used to dehumidify or dry a contained work area, and temporary heating and cooling equipment should be cleaned or wrapped before it leaves. An IEP should be engaged when the condition can't be determined or health issues are reported.
Full containment usually isn't needed just for duct cleaning, except in sensitive places like active health care facilities. Remediators should keep contaminants from being drawn into intakes, seal off the part of the system being cleaned (after an HVAC professional checks the effect), ventilate solvent fumes, and rinse cleaning residue off airside surfaces. HVAC parts with mold should be cleaned before the final evaluation or verification, and containment stays until the system is shown to be back to Condition 1. The system goes back into normal use only after a qualified professional inspects it and documents that it's clean and working as intended.
Antimicrobials never replace complete removal. Any used in an HVAC system "shall" be specifically registered by the EPA for HVAC use, risk-assessed and have detailed label directions, and if those directions can't be followed completely, they shouldn't be used at all. The same goes for coatings and sealants that claim antimicrobial performance. If an independent IEP is verifying the work, that verification should come before any opaque coating or sealant goes on, and remediators should not fog or mist antimicrobials or coatings into cavities they can't see.
Key points
- Inspect the HVAC as part of every mold job; fix the cause.
- Moldy duct liner, duct board or flex duct that can't be cleaned: replace.
- Contaminated system stays off until cleaned and repaired.
- Don't use the HVAC to dry a contained work area.
- Industry standards: IICRC S590, NADCA ACR, ACCA 6, plus the S520 for mold.
- HVAC antimicrobials must be EPA-registered for HVAC use; no fogging into hidden cavities.
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, ANSI/IICRC S520 Standard for Professional Mold Remediation — Secs. 10–10.1, HVAC remediation, cleaning and industry standards, p. 52. Best practice
- IICRC S520, ANSI/IICRC S520 Standard for Professional Mold Remediation — Secs. 10.2–10.2.4, operation before remediation, dehumidification, fungal contamination, containment and air pressure, antimicrobials and coatings, pp. 53–54. Best practice