Other things to keep in mind….
• NFPA 90A(99), Sec. 2-3.4.2 requires that service openings be identified with letters at least ½
inch in height indicating the location of the damper within.
• While inspection windows are allowed in air ducts (so long as they’re glazed with wired glass),
they do not replace the required access doors [see NFPA 90A(99), Sec. 2-3.4.4].
• Openings need to be provided in walls or ceilings to allow for access to the service openings in
your air ducts [see NFPA 90A(99), Sec. 2-3.4.5].
CAUTION: Care must be taken to ensure that any access panels or drop-in ceiling tiles
used to provide this access do not reduce the fire resistance rating of your floor-ceiling or
roof-ceiling assemblies.