International Mechanical Code

IMC 1104.1

Suction line (large line) must be insulated to prevent condensation and maintain efficiency. Uninsulated lines lose capacity and drip moisture causing water damage.

IMC 1105 / ASHRAE 15

This is correct. ASHRAE 15 and IMC require refrigerant leak detection in mechanical rooms when the refrigerant charge exceeds certain thresholds. R-410A is heavier than air, so the detector at 12" above floor is properly placed. The alarm and exhaust fan activation are required safety responses. Annual calibration meets the standard.

IMC 1203.4

Dissimilar metals (steel to copper) require dielectric unions to prevent galvanic corrosion. Without them, the pipe joint will corrode and fail within 2-5 years.

IMC 304 / Manufacturer Specs

The installation meets the manufacturer's minimum clearances. Equipment clearances are determined by the manufacturer's listing and installation instructions, which are enforced by code. As long as the actual clearances meet or exceed the listed minimums, the installation is compliant.

IMC 304.1 / Manufacturer installation instructions

While the height and distance from the register are acceptable, direct sunlight on a thermostat causes false high temperature readings, making the AC run excessively. Thermostats must be installed away from direct sunlight, heat sources, supply registers (min 3' is borderline), and exterior walls. The sunlight exposure is the primary violation here.

IMC 307.2 / ASHRAE

CRAH condensate drains must have a P-trap to prevent pressurized under-floor air from blowing back through the drain line. Without a trap, the raised floor plenum pressure will force air through the drain, preventing condensate from draining and potentially causing water damage.

IMC 307.2.2

This is a proper installation. When gravity drainage is not possible, condensate pumps are an accepted solution. The key requirement is the overflow safety switch — if the pump fails, the unit must shut down to prevent water damage. Discharge to a laundry sink is an approved indirect waste receptor.

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 501.3.1 / NFPA 110 Section 7.8

IMC Section 501.3.1 requires engine exhaust outlets to be located at least 10 feet from any building opening (door, window, or air intake). In high-rise buildings with rooftop generators, exhaust must be positioned to prevent re-entrainment of diesel exhaust into the building HVAC system. Carbon monoxide and diesel particulate entering the building during a fire emergency creates a secondary life-safety hazard.

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.

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 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 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.

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.