HVAC Remediation


The design, installation, operation, and maintenance of HVAC systems are important factors in controlling microorganism germination, growth, amplification, and dissemination. In addition, mold growth from other causes can be carried to the interior of HVAC system components where it can accumulate and degrade system operation. When system operation is affected, this can result in poor environmental control that allows widespread condensation to form. This can lead to the spread of contamination by the system and increase the scope of the mold problem by dispersing contaminants throughout a building.

Ductwork with a non-porous internal surface (e.g., galvanized sheet metal) responds well to remediation. However, sections of internally lined ductwork, duct board or flexible ductwork that are Condition 3 cannot be successfully cleaned, and therefore such ducting with Condition 3 should be removed and replaced.

13.1 HVAC Operational, Maintenance and Modification Issues

When a building is being remediated, special attention should be given to remediating the HVAC system that supports the indoor environment where remediation is taking place. Also, the HVAC system should be inspected in the manner described within this section and returned to Condition 1 as part of the overall mold remediation project. It is recommended that HVAC deficiencies be identified for correction by the customer’s HVAC service contractor. Otherwise, the remediation can fail and growth can return, adversely affecting environmental conditions within the building.

In situations with visible surface mold growth or suspected hidden growth, the cause should be identified and moisture sources controlled or corrected before remediating either the building components or the HVAC system. Remediating the HVAC system alone might not be sufficient to prevent future mold growth. The services of a qualified mechanical or professional. engineer may be needed to recommend repairs or modifications that mitigate the likelihood of reoccurring mold contamination. Implementing such recommendations is not necessarily the responsibility or within the expertise of the remediator. At a minimum, however, customers should be advised by the remediator of known HVAC conditions that put the integrity of the building at risk.


ANSI/IICRC S520: 2015 Standard for Professional Mold Remediation

13.2 HVAC Engineering Considerations

HVAC systems should be inspected for cleanliness and returned to Condition 1 as part of a building remediation. The National Air Duct Cleaners Association (NADCA) standard, Assessment, Cleaning and Restoration of HVAC Systems (ACR 2013 or current version) includes specifications for acceptable levels of cleanliness for HVAC systems and appropriate inspection techniques. It is recommended that HVAC system remediation be scheduled after other building remediation is completed in order to avoid cross-migration of particulate into the mechanical system. When this is not practical and the environment is Condition 2 or 3, HVAC system components should be isolated from the environment as part of the overall building remediation strategy. Remediated HVAC system components that can potentially be exposed to recontamination during ongoing building remediation activities should be re-assessed after building component demolition procedures and reconstruction activities are complete. Reassessment should be conducted before removing containments or other engineering controls.

When providing temporary heating, cooling, and other environmental controls within areas undergoing remediation, equipment should be decontaminated and bagged or wrapped prior to being removed from the workspace. When air-handling systems are operational, remediators should consider where to locate, containment so that contaminants are not drawn into the fresh-air intake and that the negative pressure created by the fresh-air intake does not adversely affect the pressurization differential of the contained area.

In addition to a cleanliness inspection, a complete engineering assessment of the design and working condition of the entire HVAC system should be considered, depending on the Conditions (1, 2 or 3) that exist in the project. This is especially important if temperature or relative humidity cannot be maintained within the affected area in compliance with the requirements of American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Standard 55; temperatures, relative humidity, or airflow varies between different areas of the building, or mechanical components are not in good working condition or repair. Modification to an HVAC system shall conform to applicable building codes.

Filtration upgrades should be considered in buildings that have experienced Condition 3 as part of a strategy to prevent future problems. In many cases, existing filter housings or tracks can accommodate upgraded filtration. In others, modifications should be made to the HVAC system layout to accommodate upgraded filtration. Whenever modifications are made to an HVAC system to accommodate upgraded filtration, airflow restrictions below design levels should not occur.

13.3 HVAC System Cleaning and NADCA ACR

If enough information is currently available to determine that Condition 2 or 3 exists throughout affected systems, remediation work plans, protocols, and specifications can be developed. In situations where there is visible mold growth and it cannot be determined that Condition 2 or 3 exists throughout the affected system, remediators should engage or recommend that customers or clients engage an IEP to assess the affected system.

Once the HVAC system’s condition has been assessed for cleanliness and mechanical corrections or enhancements have been completed, cleaning should be carried out in accordance with procedures described in NADCA ACR, 2013 or current version, or equivalent industry standards.

13.3.1 Use of a Mechanical System as a Dehumidification Device

Use of an HVAC system is often considered during the initial evaluation of a moisture-related problem tc asst.st in the dehumidification process. Using mechanical systems during remediation often results in the need to decontaminate the system after remediation and prior to post-


AN’SlllCRC S520: 2015 Standard for Professional Mold Remediation

remediation verification. In order to determine if the HVAC system needs remediation, it should be inspected and cleaned using the procedures outlined in the NADCA ACR 2013, or current version.

HVAC systems are not recommended for dehumidification or drying of a structure during a mold remediation project. When considering usage of an HVAC system for dehumidification, it is recommended that the following be considered:

  • operational building pressurization during HVAC usage;
  • airflow volume across the evaporative coil;
  • fresh air intake status;
  • air distribution network and potential for particle migration;
  • protection of the mechanical system for the duration of the project;
  • reheat coil operation and sequencing;
  • decontamination of the HVAC system after usage;
  • the original engineering design for the HVAC system;
  • impact on the overall building strategy; a
  • migration of particulate to unintended

13.3.2 Fungal Contamination Considerations

Determining the extent of fungal contamination present in an HVAC system can be challenging. Cleanliness criteria are set forth in NADCA ACR 2013 or current version. Multiple cleanings might be required to achieve a satisfactory level of cleanliness. On occasions, more rigorous criteria can be specified, including surface testing procedures normally used on surfaces outside of an HVAC system; however, interpretation of test results may be more difficult than with exterior environmental surfaces and air samples. Individuals procuring and interpreting such samples should be IEPs with specific training in identifying mold issues within HVAC systems.

The interior of evaporators or cooling coils can be especially difficult to clean through all layers of the coil. If a satisfactory level of cleanliness cannot be achieved, replacing coils is recommended.

Attention should be given to inspecting fan blades and blower wheels. In cases where fan and blower surfaces cannot be returned to a smooth surface condition, the component should be replaced.

HVAC components should be isolated from portions of the building where remediation is taking place. It is recommended that HVAC systems be remediated after other remediation activities have been completed. Normally it is not necessary to build containment for HVAC system cleaning. Under unusual circumstances or in sensitive locations such as active health care facilities, containment should be constructed. In addition, if an air handler is located in an equipment room that is also part of the conditioned space, containment should be constructed. Air handlers located outdoors or on rooftops require only limited containment procedures during cleaning. Remediators should use appropriate personal protective equipment while cleaning HVAC systems and isolate the portion of the system being cleaned from uncontaminated areas by blocking air ducts or supply vents. Prior to blocking these, a competent person should evaluate the impact on system operations. Sufficient ventilation is needed to dilute emissions from any cleaners used. Residue from cleaning products should be completely rinsed from surfaces before the equipment is placed back into operation.

Using an antimicrobial product may be considered to inhibit future mold growth in an HVAC system, but only after mechanical surface cleaning has been performed and the need for such treatment has been deemed necessary. Antimicrobial use should never be substituted for complete removal


ANSI/IICRC S520: 2015 Standard for Professional Mold Remediation

of mold contamination. In addition, any product used shall be specifically registered by the EPA or other applicable regulatory agency for use in HVAC systems; have undergone a risk assessment for such use; and contain specific and detailed label directions. Care should be taken to use antimicrobial products in compliance with applicable regulations. Such products shall be used in accordance with safety regulations. If label directions cannot be followed completely, antimicrobial use shall be avoided.

Remediators should understand the uses and limitations of resurfacing coatings, and communicate product use and information to the owner/client prior to application. If the project involves post remediation verification (PRV) by an IEP, the PRV should be conducted prior to application of any coating: including resurfacing coatings, repair coatings, or HVAC sealants.

Coatings and sealants used in HVAC systems which claim antimicrobial performance, shall be registered by the EPA or other applicable regulatory agency specifically for use in HVAC systems; have undergone a risk assessment for such use; and contain specific and detailed label directions. If label directions cannot be followed completely, including the use of personal protective equipment, such use shall be avoided. When coatings are used, users shall comply with EPA, state, and local regulations. Building codes and/or engineering specifications require that coatings have been tested to certain ASTM test methods as required by the performance protocols of the National Fire Protection Association (NFPA) 90A/90B. Before using any resurfacing coating, copies of this testing should be obtained from the product manufacturer. ‘

Share This