IMC 603.6

IMC 508

Kitchen exhaust systems require makeup air to replace exhausted air. Without it, the kitchen goes negative pressure causing back-drafting of gas appliances (CO hazard) and door operation issues.

IMC 508.1

IMC 508.1 requires makeup air to be provided at a rate approximately equal to the exhaust rate. At 1,200 CFM of makeup against 2,000 CFM of exhaust, the kitchen runs an 800 CFM deficit — nowhere near 'approximately equal' — and the symptoms prove it: doors that fight you and drafting problems at the gas appliances. Severe negative pressure can pull combustion products back down flues and starve burners for air. Makeup air isn't optional equipment; it's how the exhaust system is allowed to work.

IMC 603.10 (flexible duct support)

Flexible duct must be supported at intervals not exceeding 4 feet (IMC 603.10), with no more than 1/2 inch of sag per foot between supports. Supporting this run every 5 feet exceeds that maximum, so it fails. Note the 8-foot length itself is not the violation — there is no universal 5-foot length cap in the IMC, IRC, or SMACNA for flexible duct; the genuine defect here is the support spacing. Fix: add hangers so spacing never exceeds 4 feet.

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 607.5.1

All duct penetrations through fire-rated walls and floors must have fire dampers rated to match the wall rating. This is a life-safety code requirement.