IMC 607.5.1

IMC 603.6

Flexible air duct must be supported at intervals not exceeding the manufacturer’s spacing (typically 5 ft) with sag no more than 1/2 inch per foot of spacing. Excess sag chokes airflow and traps condensate.

IMC 605 (Air Filters)

Return air grille has no filter rack. All return air must be filtered before entering the air handler per mechanical code.

IMC 607 / NFPA 90A

This is a textbook-correct installation as taught in SMACNA apprenticeship programs. IMC 607 requires fire dampers at duct penetrations through fire-rated walls, and NFPA 90A requires smoke dampers at smoke barrier penetrations. Using a combination fire/smoke damper satisfies both requirements. The key elements are all present: UL listed assembly (matches the wall rating), proper sleeve (maintains the wall's fire rating), fire caulk (seals the annular space), and interlock to the fire alarm (ensures the smoke damper closes when smoke is detected). Union halls emphasize this installation because fire/smoke damper work is a high-liability specialty that commands premium wages.

IMC Section 701 / IFGC Section 304.6

This installation fails on multiple counts. First, when combustion air is drawn directly from outdoors using natural ventilation, the IMC and IFGC require TWO openings — one within 12 inches of the ceiling and one within 12 inches of the floor — to create natural convective air circulation. Only one opening is provided. Second, each opening must be sized at a minimum of 1 square inch per 4,000 BTU/hr of total input rating. For a 2,000,000 BTU/hr boiler: 2,000,000 / 4,000 = 500 square inches minimum per opening. The single 144 square inch opening is drastically undersized even if it were the only requirement. The room needs two openings of at least 500 square inches each (approximately 20 inches x 25 inches) to provide adequate combustion air for safe boiler operation.