IMC 307 is one of the most practical field sections in Chapter 3. It controls where condensate goes, how it gets there, and what has to happen when the primary drain fails. The review issue is not just pipe size - it is damage prevention.
Plain-English Summary
Fuel-burning condensing appliances and cooling coils need condensate piping to an approved place of disposal. The piping must be corrosion-resistant where required, not smaller than the appliance or pan connection, and sloped at not less than 1 percent in the direction of discharge.
Approved Discharge Path
Cooling-coil condensate must drain from the pan outlet to an approved place of disposal. It cannot discharge to a street, alley, or nuisance location. It also cannot directly connect to a plumbing drain, waste, or vent pipe. If it discharges indoors, the discharge point generally stays within the same occupancy, tenant space, or dwelling unit as the source.
Overflow Protection
Where overflow could damage building components, the design needs an auxiliary pan, separate overflow line, approved water-level detection device, or equivalent protection allowed by the section. Downflow units and coils without secondary-drain provisions need the monitoring device inside the primary drain pan.
Permit Proof Chain
Cooling coil or condensing appliance -> primary drain route -> slope -> pipe material and size -> approved discharge point -> trap or check valve where required -> auxiliary overflow protection -> concealed primary/secondary identification -> cleanout or maintenance access -> condensate pump shutdown interlock where applicable.
Masterbuild QA Lens
Review condensate as a water-damage prevention system. The highest-risk detail is equipment above finished ceilings, tenant spaces, electrical rooms, or owner-sensitive finishes with no visible overflow path and no shutdown device.
Drawing / Submittal Check
On M-101/M-501, show the drain route, disposal point, pipe size, trap or check valve, auxiliary pan or overflow device, and any pump failure shutdown. On P sheets, coordinate the approved receptor. On ceiling plans, do not hide the only maintainable cleanout behind permanent construction.
Common Review Risk
The common redline is a condensate note that says drain to nearest approved receptor without showing the receptor, slope, overflow protection, or whether the discharge stays inside the tenant/occupancy served.
Field Tip
Before ceiling close, trace the primary drain and then intentionally block the mental path: if the primary drain stops, where does the water go and what shuts the unit down? If the drawings cannot answer that, IMC 307 is incomplete.