IMC 501.3.1 / NFPA 110 Section 7.8

IMC 401.5

Outdoor air intakes and return air openings must have corrosion-resistant screens (min 1/4" mesh) to prevent entry of birds, rodents, and large debris.

IMC 501.3

Mechanical exhaust must discharge to the outdoors, not into an attic or other concealed space, to avoid dumping moisture and contaminants into the structure.

IMC 501.3 / NFPA 110 7.8

Generator exhaust must be routed away from building air intakes to prevent carbon monoxide and diesel particulate from entering the building. Most codes require a minimum separation of 15-25 feet between exhaust discharge and any air intake opening.

IMC 506.3

Kitchen exhaust ducts must be steel (min 16 gauge) or stainless steel. PVC will melt from grease-laden exhaust heat and is a severe fire hazard.

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.