The NADCA ACR standard provides a structured framework for assessing, cleaning and restoring the airside surfaces of heating, ventilation and air-conditioning systems. It explains how a project should be planned, controlled, completed and verified when conformity with the standard forms part of the agreed scope.
ACR is the NADCA Standard for Assessment, Cleaning and Restoration of HVAC Systems. It is published by the National Air Duct Cleaners Association, also known as the HVAC Inspection, Cleaning and Restoration Association, a not-for-profit trade association serving the HVAC inspection, cleaning and restoration sector. NADCA released the current 2025 edition in September 2025, replacing the earlier 2021 edition.
The standard is both a performance framework and a set of procedural provisions. It addresses the assessment of new and existing systems, the evaluation of component cleanliness, the development of a project scope, the selection of engineering controls, the use of cleaning and extraction equipment, restoration work and post-cleaning verification. It is intended for contractors, building owners, consultants, specifiers and others responsible for managing HVAC cleaning projects.
ACR applies principally to airside surfaces: the internal surfaces of ductwork and the HVAC components encountered by air as it passes through the system. A project may include supply and return ducts, air-handling units, fan sections, coils, drain pans, dampers, grilles, diffusers and associated components, but its precise extent depends on the written scope.
Conformity begins before mechanical cleaning starts. The system must first be assessed so that the need for work, the affected components, the nature of the deposit and the condition of the materials can be understood. An assessment also helps determine where access is available, whether additional service openings are needed and whether any component is too fragile or deteriorated to withstand the proposed method.
The resulting scope should identify which HVAC systems and components are included, which areas are excluded and what degree of cleanliness is to be achieved. It should also address project scheduling, building access, communication, equipment positioning, occupant protection, waste handling and any operational limitations affecting the HVAC installation. NADCA describes the standard as covering component inspections and the development of a comprehensive scope incorporating safety planning, project schedules and coordination with other parties.
Assessment is not the same as taking a few photographs through a convenient grille. Representative sections, changes in duct construction, inaccessible branches, internal insulation and important system components all need consideration. A claim that an entire system was assessed should therefore be supported by records showing which parts were inspected, how they were reached and whether any limitations remained.
The governing principle is source removal. Deposits are physically detached from HVAC surfaces and conveyed to a controlled collection device rather than merely displaced, deodorised, coated or pushed farther along the duct.
ACR describes cleaning as the use of suitable agitation to dislodge non-adhered substances, followed by capture of the released material through vacuum collection. Mechanical devices may include brushes, pneumatic tools and contact vacuum equipment, selected according to the duct material, geometry and condition. Vacuum collection is operated during the cleaning process so that loosened material is drawn towards the collection point rather than released into occupied areas.
The method must not damage the system. A rigid sheet-metal duct may tolerate a different form of agitation from flexible duct, fibrous board or an internally lined component. Where a surface cannot be cleaned to the specified condition without causing damage, repair or replacement may be more appropriate than progressively more aggressive agitation.
Conformity does not arise simply because a particular machine was used. The relevant question is whether the selected combination of access, agitation, airflow and collection removed the deposit from every component within the stated scope.
Mechanical agitation can release substantial quantities of dust and debris. The section being cleaned is therefore kept at negative pressure relative to the surrounding indoor space so that air moves into the work zone and towards the collection equipment.
The pressure differential should be maintained throughout cleaning and checked at representative locations. Duct openings, registers and other pathways may need to be sealed or zoned so that the available extraction is concentrated in the section under treatment. Protective coverings, temporary barriers or more extensive containment may be needed where work is performed above occupied areas, where access openings are being created or where the deposit could spread beyond the immediate work area.
Collection equipment exhausting inside the building should use HEPA filtration. Equipment without suitable filtration should discharge outside in a position where its exhaust, or any combustion emissions from fuel-powered machinery, cannot re-enter the building through doors, windows or outdoor-air intakes. Removed material should remain contained while it is taken out of the building.
Containment is consequently a project-specific control rather than a sheet of plastic placed beside an access point. Its adequacy depends on pressure control, sealing, equipment capacity, the occupied status of adjacent spaces and the behaviour of the material being removed.
Verification is performed after cleaning and before the system is returned to normal operation. Its purpose is to establish whether the components within the scope have reached the specified level of surface cleanliness; it does not by itself determine whether microorganisms or hazardous substances are present.
The first verification method is visual inspection. A surface is considered visibly clean when it is free of non-adhered material and debris. Adequate lighting and direct access are important because a distant photograph, an image from one convenient opening or a view of only the first section of duct cannot demonstrate the condition of the remainder of the system.
Where visual inspection is inconclusive or disputed, ACR provides additional methods. The Surface Comparison Test is intended for porous surfaces. A defined area is contact-vacuumed using a specified procedure, and the appearance of the treated area is compared with the surrounding surface; a significant visual change indicates that removable material remains.
The NADCA Vacuum Test is intended for non-porous surfaces. A template defines the sampling area, while a calibrated pump draws loosened particulate onto pre-weighed filter media without the cassette directly contacting the duct surface. The filter is subsequently weighed so that the amount of residual surface debris can be compared with the standard's acceptance criterion.
Project documentation may include before-and-after images, system drawings, inspection records, verification results, access-opening details, product information and a clear statement of unresolved limitations. Where the vacuum test is used, laboratory results and the associated sample records should form part of the completion information.
NADCA certification applies to individuals rather than companies. The Air Systems Cleaning Specialist credential recognises an individual who has passed an examination covering HVAC systems, cleaning practices, safety and relevant technical knowledge. The Certified Ventilation Inspector credential is an advanced individual qualification concerned with HVAC hygiene inspection.
An individual credential indicates that the named holder met the certification requirements in force at the time and has maintained the credential where renewal is required. It does not prove that every technician on a project is certified, that the credential holder personally supervised the work or that a particular project conformed to every provision of ACR.
A company may instead be a NADCA member. Regular member companies are required by the association to employ at least one full-time ASCS-certified person, but membership and certification remain different concepts. Membership does not convert the company itself into an ACR-certified organisation, and neither membership nor employment of a certificated individual automatically verifies the quality or completeness of a particular project.
A building owner can first check whether a claimed NADCA member appears in the association's Find a Professional directory. The directory identifies member businesses and may show the number of certificated personnel associated with each entry. NADCA also advises checking its directory or membership verification facility when a business displays the association's name or logo.
The relevant individual's name, credential and current status should then be established. A general statement that staff are "NADCA trained" is less precise than identifying the ASCS or CVI holder and explaining that person's role in the proposed project.
Project conformity should be checked separately. The contract should identify the ACR edition, the included components, exclusions, required engineering controls, acceptable cleaning methods and chosen verification procedure. Completion records should demonstrate that those provisions were actually followed rather than merely stating that the work was "to NADCA standards".
ACR is recognised international industry practice, not a legal requirement imposed on a reader in the UAE. No primary UAE instrument adopting the NADCA ACR standard as a legal requirement could be produced, and no primary document could be produced establishing a duct-cleaning contractor approval scheme in any emirate or a legally prescribed interval for general duct cleaning.
No Abu Dhabi Code of Practice specifically covers building HVAC hygiene, duct cleanliness or indoor air quality. Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life, document DM-HSD-GU119-IAQ version 4 dated 11 December 2024, is guidance rather than a binding standard.
ACR may nevertheless become contractually relevant when a building owner, consultant or specification expressly incorporates it into the project documents. In that situation, conformity arises from the agreed scope and contract, not from a general UAE legal duty.
ACR is recognised international industry practice, not a legal requirement imposed on a reader in the UAE. No primary UAE instrument adopting the NADCA ACR standard as a legal requirement could be produced, and no primary document could be produced establishing a duct-cleaning contractor approval scheme in any emirate or a legally prescribed interval for general duct cleaning.
No Abu Dhabi Code of Practice specifically covers building HVAC hygiene, duct cleanliness or indoor air quality. Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life, document DM-HSD-GU119-IAQ version 4 dated 11 December 2024, is guidance rather than a binding standard.
No. The standard provides a framework for assessment, determining the need for cleaning and completing work where cleaning is justified or specified. An inspection may conclude that a component is already acceptably clean or that repair or replacement is more appropriate.
No. NADCA certification is awarded to individuals, while companies may hold association membership. A member company is expected to have a full-time ASCS credential holder, but that does not certify every employee or every completed project.
No. The credential indicates that an individual passed the relevant examination and maintained the qualification as required. Project conformity still depends on the scope, methods, controls, verification and documentation used on that particular job.
Visual inspection is the primary method. Where the result is uncertain or disputed, the Surface Comparison Test may be used for porous components and the NADCA Vacuum Test may be used for non-porous surfaces.
No primary UAE instrument adopting ACR as a legal requirement could be produced. It remains recognised international practice and may be used voluntarily or incorporated into a contract or technical specification.