IMC 401.5
What it means on the job
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.
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- whats-wrongRooftop Unit Installation
Related IMC sections
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 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.
CraftIQ explanations are original educational commentary written in trade language and verified against the cited standards. Always confirm requirements against the code edition adopted by your jurisdiction — this is training material, not a substitute for the code book or your AHJ.