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 Principles and Practices  

Principles and practices of HVAC System Hygiene and Duct Cleaning was produced in cooperation with the DUCTBUSTERS® Franchise Network to provide all consumers of HVAC System Hygiene and duct cleaning services a general background and educational tool with regard to commonly-used techniques in air duct cleaning.
Although duct cleaning has existed for fifty years, originating in the northwestern United States, techniques have been developed for the adaptation of new technology and cleaning processes for use in humid climates.

Principles and Practices is designed to provide the consumer with information to use in comparing techniques used in the HVAC System Hygiene and duct cleaning industry. It is intended to be used by consumers as reference and educational material, and is not a scope of work.



Communications | Site Preparation | Equipment

Cleaning Methodologies | Surface Treatments | Respirators



The customer/contractor relationship is the master key in conducting a well-run project. The basic element needed to begin this process is a proper communication interchange. To establish this strong link, an HVAC System Hygiene contractor needs to provide the occupants of the facility with a clear understanding that the project will be managed properly. HVAC System Hygiene contractors and duct cleaning contractors vary in their level of knowledge of indoor air quality (IAQ); therefore, an assessment of a contractor's previous work experience can reduce the potential for improper planning and communication.

NADCA (National Air Duct Cleaners Association) has produced a Standard entitled "Mechanical Cleaning of Non-Porous Air Conveyance Systems," also known as NADCA Standard 92-01 (The Standard). The Standard is a performance assurance document which can be used to determine the depth of knowledge a duct cleaning contractor has and the level of cleanliness he will use. Properly used, The Standard can firm up the level of communication between both the duct cleaning contractor and the customer. The contractor must be aware of the overall scope of the entire project and thoroughly understand that portion of the project he is responsible for. The Standard allows a professional relationship to form between the parties, laying the foundation toward conducting and completing a successful project.

Many cleaning projects are closely tied to IAQ problems. During initial contact with a consumer, a clear understanding of the exact role of the cleaning contractor must be established. There are duct cleaning firms with the capability of providing services that extend well into the IAQ arena. However, a duct cleaner's primary concern is to provide each customer with a safe, effective method of cleaning a duct system. The customer's knowledge of duct cleaning and IAQ analysis is helpful in creating and maintaining a smooth working relationship.

A qualified HVAC System Hygiene contractor can provide the consumer with valuable information in accessing the system, project coordination, knowledge of similar systems, available techniques, development of structured scopes, product knowledge and a wide variety of other topics. More importantly, addressing concerns such as the physiological and psychological impacts the duct cleaning project may have on employees is where a duct cleaner's experience and knowledge can be valuable to a well-run job. Many of these issues should be discussed before a project is scoped or contracted.


Duct cleaning projects require a game plan. Project length can vary from a few hours to six months or more. The size and scope of a project are the two key elements which will significantly affect the length of time a project will take. Scopes of projects are written by Industrial Hygienists, customers, IAQ Consultants, duct cleaners, general contractors, or any number of other trade professionals. Even with a scope present an HVAC duct cleaning contractor's responsibility is to always use source removal during the cleaning process. The scope must contain language which allows the duct cleaner to remove all particulate. The Standard takes particulate removal one step further and provides the client and duct cleaner with a verifiable test, which can be conducted immediately after the cleaning process. The Standard is also a tool which can be used as a guide during the initial project review.

The entire project runs best when an in-depth review is conducted by the customer and contractor together to determine the expectations and obtainable results that can be achieved.

These are highlighted points which will help in the project review process:
  1. Blue prints are a must in order to conduct a project correctly. In the event blue prints are not available, be prepared to conduct extensive preliminary research.
  2. Clear timelines are needed of the project site, and schedules of building availability are essential.
  3. Site preparation and evaluation must be conducted in order to set up a firm game plan and assure the health and well-being of the building occupants.
  4. All products to be used during the cleaning process should be discussed, approved, and thoroughly understood by the customer prior to the start of the project. Material Safety Data Sheets must be provided.
  5. Consultations must be arranged with key people, such as site managers, supervisors, security and maintenance officials, who will be in charge of those areas and personnel affected by the project.
  6. Specific duct cleaning techniques should be discussed with the customer and authorized for use on the project unless techniques are specified to be used by an IAQ Consultant.
    All safety concerns of the customer, both cleaning and environmental, should be addressed.
  7. Determine if the contractor is expected to work in close cooperation with an Environmental Consultant and if a method of establishing clear communication exists.
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A successful HVAC or duct cleaning project can have beneficial results, such as reduced health risks and increased system performance. On the other hand, an unsuccessful HVAC or duct cleaning project can result in increased occupant and facility exposure to contaminants and possible mechanical system malfunctions.

To ensure a successful project, site preparation must be clearly defined from the beginning of the project. Site preparation is the process by which the contractor and customer cooperatively review and evaluate all aspects of the HVAC or duct cleaning process as it relates to the facility and its occupants, developing strategies for safe and effective management of the project.

The site evaluation must address some of the following concerns:

  • Protecting the indoor furniture
  • Occupant safety
  • Containment strategies
  • Computers and other office equipment
  • Cleaning equipment's condition
  • Building and fire safety
  • Cross-contamination assessment
  • Security
  • Specific building-related issues

Site preparation is an issue that can have a strong psychological impact on the facility's occupants. A well-planned and coordinated approach will lead to the reduction of stress employees may have relating to the cleaning project. A qualified HVAC duct cleaning company will be well-versed in site preparation. Improper site preparation can have a significant, negative impact by reducing the confidence of the building's occupants in the project and contractor, as well as creating concerns about their personal health and safety. Emphasis given to site preparation and its impact on the building occupants is important because it is one of the few visible aspects of the job. A duct cleaner's work is performed primarily above ceiling tiles or in attic spaces, so there is a tendency by the occupants to be more influenced by what can be seen. Another aspect of site preparation is the appearance of the HVAC duct cleaner's equipment. Quite often, equipment used on a project is located in plain sight.


All furniture and flooring located in close proximity to the areas to be cleaned should be covered with protective coverings. When beginning work in a new site, the occupants of that area should be informed that protective coverings will be used and that they should prepare the area accordingly. Whenever possible, furniture should be moved to allow the technicians easier access to the work site. For increased productivity, it is helpful to temporarily relocate all fragile or breakable items. Flooring should be well-protected. Some duct cleaning equipment is quite large and needs to be moved through the facility. Floor preparations can range from light coverings to plywood planking secured to the flooring for the duration of the project. Make consultations with the cleaning supervisor at the beginning of the project to determine whether or not all furniture and horizontal surfaces need to be physically wiped down after the day's work. Building occupants tend to place new emphasis on dirt found after a duct cleaning project begins.


During the duct cleaning procedure, a paramount concern must be the health, safety, and well-being of the facility's occupants. One of the primary reasons for having the HVAC and duct systems cleaned is to provide a clean, healthy environment for the people inside the facility. Both the HVAC duct cleaner and the consumer have a responsibility here. The duct cleaner's experience will be needed to determine and correct any potential safety or protection problems which may arise during the remediation process. An IAQ Consultant should be contacted to address the larger concerns of an entire facility's well-being with regard to occupant health and safety.

Address the following issues:

  1. Have all the occupants been informed in advance of the cleaning process start and stop dates?
  2. Has special attention been given to respiratory sufferers?
  3. Will the cleaning process be conducted after hours or while the building is occupied?
  4. Are components of the HVAC system such as blower wheels, supply or return grilles, and ductwork going to be removed throughout the facility during the cleaning process?
  5. What will the down time be on the HVAC system and what is the amount of time the facility needs to return to optimum temperature and humidity after cooling or heating has been restored?
  6. Are there any occupants who have high sensitivity problems to normal environment?
  7. If the occupants' workday is to continue during the process, how will large equipment and tools affect the movement and management of people?
  8. How will interrupted and/or modified security issues change normal safety guidelines in the facility?
  9. How will interrupted and/or modified fire safety issues change normal safety guidelines in the facility?
  10. Whenever communicating with building occupants, do so in writing. Unless specifically hired as an IAQ Consultant, the duct cleaner's responsibility is to assure occupant safety with regard to the specific procedures involved in cleaning the HVAC system and duct network.


Much of the particulate removed from a duct system is not considered hazardous waste; however, it is prudent to observe proper environmental containment strategies during all HVAC duct cleaning projects. The goal of any containment strategy is to move gross particulate and microbiologicals in an orderly manner from the point of removal to the point of capture without cross contaminating the indoor environment. Individual strategies may differ from one duct cleaner to another. An experienced duct cleaner draws heavily on prior knowledge, especially during complex commercial cleaning projects.

The type of equipment used by a duct cleaner has a strong influence on his containment strategy selection. For example, the strength of a negative pressure generator will have direct bearing upon the length of ductwork which can be cleaned from a single hookup point. When analyzing containment strategies with a duct cleaner, expect specific answers from him during the estimating process to assure a complete and professional job. Discussion of containment strategies will also give an insight into the project as no other method will.

Use the following questions to prepare containment strategies:

  1. Will a negative pressure generator be used to keep the ductwork under a negative pressure while cleaning is being performed? Will the generator remain running to pull all airborne contaminants toward itself?
  2. How powerful is the negative pressure generator (usually this is rated by CFM)? The amount of suction the device has will have a direct effect on the length of duct which can be cleaned.
  3. Will the negative pressure generator be located inside or outside the facility during the cleaning process? If located inside, does it have HEPA (High Efficiency Particle Arrestance) filtration?
  4. What length of duct can be cleaned (based on height and width of the duct) before significant loss of negative pressure occurs within the system?
  5. Where is the starting and ending point of each work cycle's activity?
  6. In what direction will the particulate be moved and how will it be captured?
  7. Will supply and return registers be sealed or removed, and has cross- contamination during the cleaning process been considered?
  8. Has the specific cleaning strategy been used before and in which verifiable projects?
  9. Is the proposed cleaning strategy counterproductive, by adding unnecessary labor or product to the project?
  10. Does the strategy consider the client's existing safety plans?
  11. What is the facility protection plan for contaminated equipment in both movement and breakdown?
  12. Verify that a system is in place for all aspects of containment during the cleaning process. Without a clear understanding between the customer and contractor about particulate movement and containment, the project relies solely on the cleaning technician's best judgment.


During site preparation, special attention should be given to all electronic equipment throughout the facility. A duct cleaner will be working in close proximity to highly sensitive equipment; in some cases, directly above the equipment. Water will be used when HVAC coils are being cleaned.

To prepare electronic equipment for the cleaning process, first determine if moving the equipment is possible. If movement is not possible, the equipment must be covered. Avoid covering electronic equipment with plastic or heat-restrictive coverings unless the equipment will be shut down during cleaning. Make sure the user of the equipment has been notified about the cleaning being conducted in their work area.


The condition of an HVAC duct cleaner's equipment is a direct indicator of the level of professionalism a customer can expect on a project. Equipment must be in good condition at all times. Special attention needs to be given to the collection equipment, especially if it is homemade or equipment built "in-house." Whenever possible, a duct cleaner should be selected who uses professionally designed and constructed equipment with a proven track record.

When inspecting a duct cleaner's equipment, take the following items into consideration:

  1. Vacuum equipment must be clean and cabinets must fit well. Improperly fitted seams are a potential contamination problem to the indoor environment.
  2. All equipment must be sealed when entering the facility.
  3. When a project is starting, all equipment must be completely cleaned before being brought into the environment.
  4. Vacuum hoses must be in good condition, free from holes, tears, or leaks.
  5. Air compressors used inside the facility must be free from oil leakage.
  6. All wheels on rolling equipment must function properly so that flooring will not be harmed when equipment is transported throughout the facility.
  7. Equipment which fails to meet these minimum requirements should prompt further review of the cleaning process.


Duct cleaning projects require both the customer and the duct cleaner to understand the safety and fire procedures of the facility. Most commercial HVAC systems have alarms built into the ductwork which are designed to detect smoke and heat. These systems require bypassing during the cleaning procedure to prevent false alarms and damage to the alarm components. All concerned parties should be made aware that normal fire and safety policies will be altered during the cleaning project, including the fire department and facility security. All alarms need to be verified for operation after each work period.


As the site preparation progresses, a cross-contamination assessment needs to be conducted. This evaluation must take into consideration all of the possibilities for allowing particulate and microbial contaminants, located within the duct system, to enter into the facility during the cleaning project. Another source for cross- contamination would be the use of equipment already contaminated from a prior cleaning project. Cleaning techniques vary greatly from one duct cleaner to another, and the potential for environmental cross-contamination will also vary according to the procedure being used.

When specifying The Standard as a source document, the issue of contamination is specifically addressed. A good example of cross-contamination would be the dislodging of particulate from the ductwork with the HVAC system fan running and open supply grille outlets into the environment. Cross contamination will also lead to greater problems. Once a facility has been contaminated, an assessment will be needed to determine the level of cleanliness of the indoor environment, and if a cleaning of all interior surfaces will be necessary.


Along with protecting the indoor air quality of the facility, the duct cleaner is tasked to address unusual security conditions. Projects conducted during off or unusual hours will require changes in normal security to a building. Alarm systems and companies need to be notified well in advance. Security teams on larger locations need to be advised that outside doors and windows may be opened. In general, the normal facility security for that work area will be altered.


The experience of a duct cleaner becomes far more important as specific and unique projects arise. If the facility has special requirements, it becomes essential to have a contractor who can draw from a wide variety of previous successful projects. It is the client's responsibility to evaluate and compare a number of duct cleaners and their techniques to determine which will work best in their situation.

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There are a few pieces of equipment which are specific to the industry. They are:

  • Negative pressure generator or collection device
  • Air compressor or some form of pressure supply
  • Hand HEPA vacuums and wet vacuums
  • Paint sprayers for application of coatings

This equipment will determine, to a large degree, how the cleaning project will be conducted. When contracting with a reputable cleaning firm, ensure that some form of this industry-specific equipment will be used. Verify that the equipment is in good condition. The duct cleaning industry requires that equipment which cleans contaminants from a duct system is strictly filtered and maintained to prevent cross- contamination. There should be no hesitation in questioning any piece of equipment brought into a facility. The Standard specifically addresses equipment related issues.


"Negative pressure generator" or "collection device" are the terms designating the mechanism used to create a negative, or reverse, airflow within the ductwork with sufficient velocity to prevent cross contamination during the cleaning process. This unit should always be HEPA filtered when located within the facility. These HEPA filters must have a D.O.P. test number indicating that they have passed all testing.

The generator can be used during the cleaning process in a number of ways. If the duct size is small enough, or short enough, the unit may be capable of creating enough velocity to draw all the loose particulate through the duct system. This technique is widely used in the residential arena. Another technique will use the device to generate an overall negative pressure while the system is being cleaned with contact vacuums or brushing and air sweeping. The duct cleaner is responsible for maintaining sufficient negative pressure within the duct system to prevent any possibility of cross- contamination.

The two main categories of this type of equipment are truck-mounted units and portable units. Both types have their place and are used widely throughout the country.


Many of the tools and devices which are used are pneumatically powered. This requires the use of large amounts of pressure to be supplied to these tools. The most common method of supplying this pressure is through the use of an air compressor. Gasoline or petroleum-powered compressors must always be located outside the facility, with precautions taken during site preparation to prevent fumes from entering the facility. Electric compressors can be located within the facility during the cleaning process. A third type of pressure supply used in the industry is dry nitrogen gas. Nitrogen is capable of reaching much higher pressures and can be more effective with various tools. Generally, expect to see some form of pressure supply device on any serious duct cleaning.


Hand vacuums are commonly used by duct cleaners for a variety of tasks. Expect to see this type of vacuum on location. HEPA filtration is an absolute must on these vacuums, especially when the wet vacuums are being used to clean microbiological contaminants from the drain pan and evaporator coil area within the facility. The duct cleaner must be able to demonstrate exactly how the vacuum is being filtered. This is important because many wet vacuums are not manufactured with HEPA filtration and this equipment may be located within the facility during the cleaning project.


Paint sprayers are another tool in the duct cleaner's arsenal. This tool will be used when the duct cleaner has been contracted to either re-coat the ductworks' duct lining insulation or to apply a coating within the HVAC unit.

Duct cleaning equipment should always be in good condition and well maintained in a professional manner.

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Currently, there are several different methods and combinations of methods which are used regularly to clean HVAC and duct systems. There is no regulatory endorsement of any specific method as long as that method or combination of methods will achieve the levels of cleanliness required by The Standard. Each cleaning method has it's strong and weak points. One factor affecting cleaning methodologies is the location of the project. Regional climates are a general divider of technique in the HVAC duct cleaning industry. The two climate regions are high and low humidity areas. High humidity regions can cause severe buildup of mold, mildew, yeasts, and bacteria. These buildups require more aggressive cleaning techniques when addressing the HVAC unit itself.

Some methods have been used successfully for over fifty years with little or no change in the technology. The method selected for cleaning a facility lies with the customer. Many times the customer does not spend enough time in the area of specifying the exact method desired because of assurances by the cleaner that the end result will be the same. This is acceptable if the duct cleaner is held to The Standard levels and there is a definite plan to verify the cleanliness of the project as it progresses. Approving cleaning methods for a project means little without a verification program. Many times, if the client is uncomfortable about self-verification, a third party can be brought in to oversee the verification. When focusing on the end product of cleanliness, a verification of cleaning methods must weigh heavily on its ability to address the well-being of the indoor environment. It is the duct cleaner's responsibility to make the cleaning methods function properly. There are a few methods described below which will assist in developing a sound cleaning procedure during the estimating process.


The negative pressure generator is perhaps the most commonly used and recognized piece of equipment in HVAC duct cleaning. For many firms this one piece of equipment is the axle around which all cleaning techniques revolve.

Although there are many brands and types of these units available on the market, there are only a few basic facts to be dealt with. The most obvious difference between generators is that some are mounted on a truck which is driven to the location, and others are not mounted, but are usually transported to the project location inside a truck or trailer.

When choosing a negative pressure generator, determine whether or not the following factors apply:

  1. Accessibility into facility to be cleaned
  2. The discharge of particulate and method of contaminant storage
  3. The number of floors a facility has and how it will affect equipment use
  4. Maintenance and up-keep of the cleaning equipment
  5. Storage of equipment during the cleaning project
  6. Isolation capabilities of the generator to contain removed particulate
  7. Power accessibility and voltages (types of power or fuel). Some are gas, some are electric
  8. Ability to comply with industry standards (Has cabinet been tested with HEPA filtration?)
  9. The negative pressure generator is critical on commercial/industrial projects to maintain negative pressure on the duct network during cleaning. In any duct system this type of vacuum is invaluable in maintaining the purity of the indoor environment.

Although ducts can be cleaned in many ways, cleaning a system without a generator can cause:

  1. Polluting of the indoor environment
  2. Improper movement or removal of particulate
  3. Cross-contamination of facility
  4. Increased labor and project length

The size of the ducts, type of duct construction and dirt in the duct all need to be taken into consideration when trying to determine the velocity of air movement needed to entrain particulate into the air and back to the negative pressure generator. A high-CFM generator alone will not get a duct clean. When using portable equipment in the indoor environment, NADCA Standards require that special, high-efficiency filtration (HEPA) be used to prevent any possibility of particles from entering back into the environment.


Air washing and sweeping are methods used to dislodge particulate from the inside walls of the duct. They are all, by definition, a mechanical means of agitating the ductwork's interior surface, loosening debris which has accumulated on the surface of the duct walls. These methods are rarely used alone and are normally used in conjunction with a negative pressure generator. These techniques will vary greatly according to the type of duct being cleaned. Metallic ducts with no internal lining can be cleaned quite thoroughly and easily with aggressive cleaning methods. Caution must always be used, however, when using any mechanical agitation on fiberglass products. The mechanical agitation of ductwork is widely accepted as one of the essential methods of duct cleaning.


The term brushing is exactly what the name implies - the duct cleaner will use this technique when trying to get the system as clean as possible without washing or hand wiping. The duct cleaner may employ a wide variety of brush types depending upon the type of duct to be cleaned and the type of contaminant present. Some brushes are attached to extension wands and used by technicians to physically brush the surface inside the HVAC unit. Other brushes may be attached to automatic rotating heads which spin inside the duct system, dislodging debris. These brushes are either pneumatic (Air pressure) or cable-driven.

No standards currently exist to determine the effects of different types of brushes and bristles on various duct surfaces. It is accepted that metal ductwork with no internal liner can withstand very aggressive brushing techniques. Fiberglass liner and ductboard rely more upon the individual cleaning company's professionalism and experience with the product, but can be cleaned successfully using the same type of techniques. The brushing technique is an important item to consider when contracting with a cleaning firm. Air washing alone may not always enable the duct cleaner to achieve the cleanliness levels set by The Standard.


Hand or contact vacuuming is another technique used by duct cleaners. Hand vacuums brush and lift particulate from a duct or HVAC surface in one motion. All hand vacuums must follow strict procedures for filtration if located inside the facility or home. Hand vacuuming is a popular method used on ductboard, ducts, internally-insulated ducts or thermal insulation located within an HVAC unit.

This type of vacuum is helpful when trying to penetrate deep within porous surfaces to remove particulate. Hand vacuums are used to vacuum off coils before cleaning and can be used as wet vacuums to clean drain pan sludge. Most hand vacuums provide the cleaning technician with versatility in unusual circumstances. Hand vacuums should be selected which use a primary capture bag to allow for easy disposal of any substance collected. This type of vacuum will actually aid in the cleanup of a high-CFM vacuum.


Gaining access into the duct network can be handled in several ways. Specific hand tools are made to create square and centered access holes which leave safe entry ports for future inspection.

Two common closure methods of these access holes are the use of pre-fabricated access doors, which allows simple future access, and the use of access plates which are permanently attached and sealed onto the ductwork.

Access doors and plates both require the penetration of the duct and insulation. Insulation should be handled in accordance with NAIMA's guideline for cleaning fibrous glass insulation or duct systems to prevent future condensation problems from occurring

Contractors can identify the types of access and entry which will be used throughout the cleaning project and inform the customer of special conditions requiring alternate methods. The opening and closure methods used on ductboard will differ greatly from the methods used on metallic ductwork. Projects having several types of ductwork must be analyzed for all opening and closure methods to be used.

Improperly sealed openings can create duct leakage, future IAQ problems and air flow imbalance. All access doors must be installed according to manufacturer's specifications and all access plates should be sealed with a UL181 mastic and be in accordance with SMACNA standards.


Breakdown and cleanup are issues which may have a strong psychological impact on a cleaning project. The duct cleaner is responsible for making sure that all equipment is removed from a facility in a fashion which will not cause cross contamination. This means that negative pressure generators, or collection devices, which were located within the facility, should not be opened, exposing contaminants to the indoor environment without proper procedures being in place. The same holds true for all other equipment and tools the contractor uses during the process.

Cleanup of the facility can be addressed in two ways: total breakdown and cleanup directly after completion required in short-term projects; and cleanup on a shift by shift basis, or as movement progresses through the facility, which is necessary on long-term projects. When contracting a duct cleaner, be certain to address the level of cleanup expected at the end of each cleaning cycle.

Some projects require extensive cleaning of all horizontal surfaces after an area has been completed. This is due to the fact that occupants of the facility tend to think any existing debris on a horizontal surface could have been a direct result of the cleaning process, raising unnecessary alarm. Well coordinated projects will have normal cleaning of the facility scheduled at the completion of the duct cleaning. A quality HVAC duct cleaning company will have a strong system in place to clean up a facility after the work has been completed. A leading indicator of the quality of breakdown and cleanup can be assessed during the initial site preparation. One of the items to address is where the dirt and debris removed from the facility will be discarded.

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In the past, the issue of using any surface treatment as a method of cleaning ducts has been controversial. Surface treatments, when used alone, will not provide the consumer with a clean duct. Source removal of the organic and inert contaminants within the duct system must be the primary method utilized to perform HVAC duct system cleaning in accordance with The Standard. One of the reasons for much of the controversy was created by the constant application of non-EPA registered products to duct surfaces. A second reason for debate was the general misapplication of all these surface treatments. In theory, the application of a coating to a fiberglass duct surface which is beginning to degrade has great appeal. The creation of a new interior surface to the duct system without the replacement of that system can greatly offset replacement costs.

One of the factors which will affect a consumers decision whether to use these products is the regionality of the project. Areas of the country which have high humidity tend to be relying on surface treatments far greater than low humidity regions. The difference between the two regions is the ability for microbiological contaminants to live and grow within the duct system. Most surface treatments have some level of biological control with some being specifically designed to eliminate or reduce these types of contaminants. When considering the application of surface treatments it is essential to secure the EPA registration number for that specific product. NFPA 90a, NFPA 90b and Underwriters Laboratories UL181 should also be consulted during the approval process.

It is generally accepted that surface treatments are employed after the ducts have undergone a thorough source-removal process. The use of these surface treatments alone, on non-cleaned surfaces, should never be accepted as a method of cleaning ducts. Surface treatments have the ability to solve many customer concerns, such as fiberglass surface integrity problems and an alternate method of microbiological control. Most surface treatments fall into two categories: coatings and biocide treatments.


Coatings fall into two general categories: those that are designed to resurface the duct and those that provide a long-term treatment for microbiological growth. Some coatings address both of these categories. Many coatings are used in the duct cleaning industry to aid in complex problems which can exist when cleaning fiberglass-lined ductwork and ductboard-lined ducts. Even though coatings are used primarily on fiberglass surfaces, it is not uncommon to find them used on metallic surfaces, making use of their antimicrobial properties. All coatings must have proper registration with the EPA for specific use on the inside of the ductwork. Fiberglass insulation within the HVAC unit is the most likely surface to require coating. An assessment of the integrity of the fiberglass liner or ducts is generally made to determine whether coating or replacement is necessary.


The second type of surface treatment which is used in the cleaning of duct systems is the application of a liquid biocide to all duct interior surfaces. This type of treatment is generally conducted after the ducts have undergone a thorough source removal process. These treatments are also applied to clean ducts as a preventive maintenance measure. All biocides must carry full EPA registration for the specific applications they will be used for. Biocides are products which allow the duct cleaning contractor to sanitize, and in some cases, disinfect an air duct system. Manufacturer's specifications must be strictly followed by the contractor when mixing and applying these products.


Barriers are used as a surface treatment to significantly reduce the absorption and retention of moisture by porous surfaces, thereby minimizing future microbiological growth. Surface barriers are applied only after the ducts have undergone a thorough source removal process. Liners and barriers provide an easily cleaned surface, which aids in long-term maintenance of the unit.

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The objectives of this section are to increase awareness of on-the-job safety issues and to encourage basic safety guidelines. Respiratory protection is required to be worn whenever work is being conducted on the HVAC/duct system. Respirators are available in various sizes, shapes, and configurations. Their primary purpose is to protect the duct cleaner's health and well-being. There are two kinds of respirators -- air-purifying respirators and supplied-air respirators. Air-purifying respirators are available in several varieties, including disposable respirators, half-mask and full-face respirators. Supplied-air respirators come in three types:

  1. Loose-fitting (Full Suit)
  2. Air-line
  3. Self-Contained Breathing Apparatus (SCBA)

Air purifying respirators are recommended for most residential, commercial and industrial jobs where no chemicals are being used and where there is no oxygen deficiency. In confined spaces and areas where chemicals are being used, a supplied-air respirator should always be worn.

All respirators must meet OSHA, NIOSH and ANSI standards. Always follow manufacturer's instructions on use, fit and care of a respirator. An approved negative-pressure, half-face respirator with fit test and appropriate filtration is acceptable for typical residential duct cleaning projects.

Duct cleaning itself is the business of dislodging particulate which has remained in a static condition for a long period of time. It is therefore essential to maintain constant vigilance over all cleaning projects when it comes to proper respirator use. Whenever a duct or HVAC unit is accessed, viewed, inspected or cleaned, proper respiratory protection is required. A determination of the type of contaminants present in a HVAC/duct system should be made in order to select the specific respirator needed for each cleaning project.

The proper fitting of a respirator is essential for assuring the filtering integrity. Many of these issues fall under OSHA compliance; therefore, an intimate under-standing of these regulations is required by all duct cleaning firms.


The duct cleaning industry makes use of just about every type respirator available. Each cleaning project is subject to changes as to the type of mask and cartridges being used. The range begins at the basic nuisance- dust-type paper respirators. These respirators are at the bottom of the scale and are not generally used for serious cleaning projects. These masks afford minimal protection to the cleaning technician and should not be used on a duct cleaning project.

The next level is the half-face respirator. It is designed to cover the nose and mouth with an air-tight seal to prevent particulate from entering the side of the respirator, violating the filter cartridge integrity. This type of respirator can be coupled with various removable cartridges which allows it to filter a variety of airborne contaminants. The half-face respirator affords no protection to the user's eyes and must be used with safety glasses.

A full-face respirator is designed to cover the technician's entire face, forming an air-tight seal. The mask will give the eyes maximum protection when air washing or aggressive cleaning techniques are used. Many duct cleaning techniques cause constant loose debris to move across the technician's face, and is quite common when using standard duct cleaning methods. This mask is one of the duct cleaner's preferred tools and is widely accepted as standard issue for maximum protection.

The PAPR, or Powered Air Purifying Respirators, are the next level in proper respirators. These respirators are designed to supply a constant flow of air to the duct cleaner and minimize strain put on the lungs. These respirators draw air from the surrounding area and are directly influenced by the condition of that air. Filtration selection, therefore, is important for the type of contaminants being removed. PAPR's are very effective in keeping the technician less stressed and cooler during the cleaning process.

Supplied-air respirators have a constant flow of air supplied to the technician through a pipeline or hose. The air is drawn from a remote area, filtered, then sent to the technician. This type of respirator is selected, as with all respirators, based on environmental characteristics. Always consider the following before selecting a respirator: Before choosing a respirator, the exact contaminant in the workplace must be identified. First, determine the concentration of the contaminant in the air. Next decide what form the contaminant is in (gas, vapor, dust, mist, or a combination).

Another important consideration is how long the technician will be exposed.

Other questions to consider before selecting a respirator:

  • Does the respirator irritate the skin, nose, or eyes?
  • What is the PEL (Permissible Exposure Limit) of the contaminant?
  • Is the contaminant above the IDLH (Immediately Dangerous to Life or Health) level?
  • Is there less than 19.5% oxygen in the workplace?


OSHA Standard § 1910.133 (10) states: Persons should not be assigned to tasks requiring use of respirators unless it has been determined that they are physically able to perform the work and use the equipment. A local physician shall determine what health and physical conditions are pertinent. The respirator user's medical status shall be reviewed annually.


All respirators must be inspected for wear and deterioration of their components before and after each use. Special attention should be given to rubber or plastic parts which can deteriorate. The face piece, especially the face seal surface, headband, valves, connecting tube, fittings, and canister, must be in good condition. A respirator inspection must include a check of the tightness of the connections. Chemical cartridges and gas mask canisters should be replaced as necessary to provide complete protection. Mechanical filters must be replaced as necessary to avoid high resistance to breathing.

Buster Enterprises, Inc. Copyright 1994,1995

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