HVAC Condensate Rules — Primary Drains, Pans & Float Switches
Condensate seems trivial until an attic air handler dumps water through a ceiling. The IRC’s answer is layered protection: a primary drain to an approved location, plus a second line of defense — an auxiliary pan, a separate overflow drain, or a float switch — anywhere a clogged drain would cause damage. The details are in M1411.
Worth knowing
- The trap question is answered by the equipment, not the code book: negative-pressure (draw-through) air handlers need a trap of the depth shown in the installation manual or the drain won’t flow at all — and an untrapped drain on such a unit sucks air and spits water.
- Terminate the auxiliary pan drain somewhere the homeowner can’t miss — over a window or entry door is the classic choice — because water from that pipe is the only warning before the float switch era.
- Float switches beat pan drains in retrofit work because they need no new piping, but they shut off cooling when they trip; in server rooms or hot climates, pair the switch with a maintenance habit, not instead of one.
- Condensate pumps are permitted where gravity drainage is impossible, but the pump’s overflow switch should be wired to shut down or alarm the equipment — a dead pump is just a slow-motion flood otherwise.
Common questions
What does the code say about primary drain for HVAC Condensate Disposal?
Condensate from cooling coils and condensing appliances must be conveyed to an approved disposal location and must not discharge onto streets, sidewalks, or where it creates a nuisance. (IRC M1411.3)
What does the code say about secondary protection for HVAC Condensate Disposal?
Where a blocked primary drain could damage building components (attics, above ceilings, finished spaces), the code requires one of the listed options: an auxiliary pan with its own drain, a separate overflow drain from the coil, or a water-level shutoff device. (IRC M1411.3.1)
What does the code say about auxiliary pan specs for HVAC Condensate Disposal?
The auxiliary pan must be at least 1½ inches deep, extend beyond the equipment footprint, be corrosion-resistant, and drain through a minimum ¾-inch pipe to a conspicuous point of disposal so the owner notices it running. (IRC M1411.3.1)
Adopted edition by state
Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.