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DUCT CLEANING (Pros and Cons)




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HVAC Inspection / Maintenance

     A properly designed and balanced HVAC system equipped with the highest efficiency air filtration recommended by the manufacturer is the best approach to minimize IAQ complaints. In new construction, HVAC systems are designed for specific use patterns, occupancy and air volumes. IAQ complaints associated with new construction are typically fixed ("tweaked") by the HVAC system designer/engineer and are short-term in nature. Other IAQ complaints are primarily associated with the installation of new building materials.

     AET's experience indicates that IAQ problems primarily occur as a result of renovations, changes in building use and/or occupancy, as well as normal aging and wear of the HVAC system. Remember, minimum air volumes provided by your HVAC system are based on the date of the facility construction which in many cases, is less than today's standards.

A Winning Combination

  • Facilities Management - HVAC modification is an essential component of building renovation and property conversions. Thorough planning and technical assistance by the ventilation engineer is required. Strict controls of the renovation process must be maintained by building management throughout the course of work.
  • Building Engineer - Daily inspection, maintenance and operation of the building's HVAC system rests in these capable hands. Their knowledge is dependent on site specific training provided. All too often, specific knowledge of the building HVAC system is lost due to employee turnover or retirement.
  • Contracted HVAC Specialist - Regular (at least annual) inspection and maintenance of the facility's HVAC system should be provided by an outside service provider including cleaning cooling coils and drain pans. Make sure site visits include short training sessions (question/answer) for your HVAC system maintenance staff.

Duct Cleaning: Pros and Cons

     Surface dust inside HVAC duct work is present even in new construction and gradually builds up over time. The extent of build-up is a function of the efficiency of air filtration provided at the fresh air intakes, interior duct transitions and re-entrainment of airborne dusts in return air. In general, surface dust adheres to the duct surfaces and does not necessarily extend to the occupied space. The EPA reports duct cleaning has never been shown to prevent health problems. Further, review of available research on duct cleaning does not indicate a significant reduction in airborne dust levels in occupied space once completed. AET's experience with airborne dust levels in commercial buildings indicates levels are normally less than 1/100th of OSHA's PEL Standard.

So Why Perform Duct Cleaning?

  1. Dust Discharge: Duct cleaning is a viable option where ducts are clogged with sufficient dust and debris to release visible dusts from the supply air exhausts. Best results are demonstrated with sheet metal ducts and semi-porous ducts (plaster or concrete). See "internally lined duct work" below.
  2. Aesthetic Reasons: Duct cleaning can be viewed  as a proactive 1st step in HVAC maintenance especially during property conversion. Remote photography inside the duct can be use to verify/document the extent of cleaning (i.e. before and after photos).
  3. Operational Reasons: Some research suggests that duct cleaning may improve the efficiency of the HVAC system, resulting in a long operating life, as well as some energy and maintenance cost savings. Reportedly, this benefit can be achieved where the whole system is cleaned (not just the duct work).
  4. Toxicity of Surface Dusts: The types of contaminants in surface dusts reflect past uses/operations performed within the facility as well as outside air conditions from industrial neighbors. The decision to clean, replace or just to do nothing, should be based on a visual inspection, surface dust sampling and a well-defined project specific clearance protocol where cleaning is chosen.

Case Studies Involving Toxic Surface Dusts Completed by AET Include:

  • Asbestos
  • Mold
  • Lead and Other Toxic Metals
  • Vermin (Rodent and Insect Infestation)

     Where duct cleaning is performed, all components of the HVAC system must be cleaned including supply and return air ducts, registers, grills and diffusers, heat exchangers, heating and cooling coils, condensate drain pans, fan motors and fan housing and the air handling unit housing. Failure to clean a component of a contaminated system can result in re-contamination of the entire system. Duct cleaning should be performed by a National Air Duct Cleaner Association (NADCA) contractor utilizing NADCA recommended practices and standards.

Biocides and Sealants

     The purpose of duct cleaning is to remove accumulated dust and other contaminants (not to add a "non-toxic" chemical) to the duct work interior. Remember, biocides are anti-microbial products (like pesticides) designed to kill, control, disinfect or sanitize microbiological contaminants and are toxic.

     Reportedly, the EPA has registered approximately 16 anti-microbial products for use in HVAC duct work. However, the EPA assessment protocol does not have an acceptable efficacy method to show that a product can either sanitize of disinfect a HVAC system. Further, no chemical biocides are currently registered by the EPA for use in internally-insulated air duct systems.

     Before biocides and sealants are applied, the type and intended use of these products should be investigated by the facility owner and/or their environmental consultant. Biocide application must follow specific instructions on the product label and be applied after the system has been properly cleaned. There are several reported instances and case studies where biocide/sealant products have been used where building occupants became ill during and after application.

Internally-Lined Duct Work

     Increasingly, sheet metal ducts internally lined with fiberglass or constructed with fiberglass duct board are being used in new construction. The North American Insulation Manufacturers Association (NAIMA) has prepared recommendations to perform duct cleaning on insulated ducts. Cleaning must follow strict protocols to not damage the fiberglass insulation. Again, no chemical biocides are currently registered by the EPA for internally-insulated air duct systems. Most experts agree when this duct work gets wet and exhibits mold, it cannot be cleaned and must be removed and replaced.

Best Ways to Prevent Dirt From Entering the HVAC System

  • Use the highest efficiency air filter recommended by the manufacturer for your system. Do not over filter, due to air flow restriction concerns.
  • Change filters regularly. Increase filter inspection and changing during times of construction or renovation work. Where feasible, seal off return air registers and do not operate your HVAC system during construction/renovations including cleanup of dusts. Use of multiple sequential filters can save some expense.
  • Be sure all filters are in place so that air cannot bypass filters through gaps in the filter holder/rack.
  • Have your HVAC system regularly inspected and maintained by the outside HVAC contractor. Clean cooling coils and drain pans regularly.
  • Perform regular cleaning and custodial work to remove surface dust throughout your facility. Vacuuming can increase the amount of dust in the air depending upon the efficiency of the filter in your vacuum. Vacuum in-place supply or return registers which exhibit visible dust levels.

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