Leaving a job site carries with it new responsibilities for the air duct installation contractor. A brand new duct system filled with construction dust and debris cannot be expected to operate to clean air standards and can impact performance of the building's mechanical system.

The Sheet Metal and Air Conditioning Contractors' National Association (SMACNA) recently published "Duct Cleanliness for New Construction Guidelines." It is intended to help commercial duct installation contractors, engineers and building owners towards achieving a clean, full-performance duct system.

"Designers are starting to recognize the need for more duct access panels near major duct transitions and along long sections of straight ductwork, in addition to those normally required near fire dampers and fans," according to the guidelines.

"Special attention to duct access is also important at the top and bottom of vertical ducts having multiple floor penetrations.

"Prior to the 1970s, duct systems in commercial buildings were installed and buried behind walls and ceilings, and access to the interior of these duct systems was not identified as necessary. Duct systems are becoming a serviceable maintenance item in commercial buildings due to indoor air quality (IAQ) issues, and the proper quantity, size, and location of duct access panels require more definition in new construction design documents."

How clean or dirty a duct system is can be very subjective and difficult to assess or measure. Therefore, SMACNA recommends three generic levels of duct cleanliness: Basic, Intermediate and Advanced. The Basic level should be assumed unless noted otherwise.

The Basic guidelines detail the condition the ductwork should be in as it leaves the manufacturer: light zinc oxide coating on the metal surface, for example, as well as details on delivery to the site, inspection prior to installation, covering the risers, etc.

At the Intermediate level, more precautions are taken, such as storing the ductwork in a clean, dry place on-site prior to installation, with limited exposure to dust. In addition, the installation area should be clean and dry and protected from the elements. There are even more stringent requirements for the Advanced level.

Members of the duct cleaning task force include: Randy Novak, Novak Heating & AC, Cedar Rapids, Iowa; Peter Vath, Heritage Air Systems, Deer Park, N.Y.; Eli Howard, SMACNA staff; Craig Benson, Paramount Sheet Metal, Port Coquitlam, British Columbia, Canada; Jeff Chase, Cox Engineering Co., Canton, Mass.; and Jeff Yago, technical writer.

The guidelines are available for free download to non-members as well as members at www.smacna.org.

SMACNA can be contacted at 703-803-2980; fax 703-803-3732.