Putting an air handler in an attic over a finished ceiling.

Condensate Overflow Protection Requirements (IRC P314.2 / IMC 304.2):

1. Primary Drain Pan: Must have a drain pan under the cooling coil (IRC P314.2).

1. Overflow Protection: One of the following is required: - Secondary Drain Line: A separate drain line connected to the primary pan's overflow outlet, routed to an interior or exterior location (IRC P314.2.1). - Auxiliary Drain Pan: A secondary pan beneath the unit with its own drain line (IRC P314.2.2). - Overflow Switch: A device (e.g., float switch, condensate pump overflow switch) that shuts off the unit when the primary drain is blocked (IRC P314.2.3).

1. Attic Installation Specifics: - If the air handler is over a finished ceiling, an overflow switch or secondary drain pan is mandatory to prevent water damage (IRC P314.2.3). - The overflow switch must be installed on the primary drain line or in the primary drain pan (IRC P314.2.3). - If using a secondary drain pan, it must be sized to hold at least the condensate volume of the largest coil (IRC P314.2.2).

1. Drain Line Materials: Must comply with local plumbing codes (typically PVC or ABS).

Recommendation: Install a condensate overflow switch (e.g., float switch) on the primary drain line or pan. This is the most common and code-compliant solution for attic installations over finished ceilings.

Note: Local amendments may apply. Check with your AHJ. If unsure, consult a licensed HVAC technician.

IRC M1411.3 / IMC 307.2.3 requires primary and secondary (overflow) protection for attic air handlers. Since you are over a finished ceiling, you cannot rely solely on a pan drain.

Required Setup (choose one per IMC 307.2.3):

1. Primary: Condensate line trapped & routed to approved disposal (IMC 307.1).
2. Secondary (Overflow) — Pick ONE: Auxiliary Drain Pan (IMC 307.2.3.1): Min 1.5" deep, 3" wider than unit footprint. Drain line must terminate conspicuously (e.g., over a window/door, soffit) where occupant sees dripping. No trap required on pan outlet. Overflow Shutoff Switch (IMC 307.2.3.2): Float switch in primary drain line downstream of trap OR in auxiliary pan. Must kill power to unit (thermostat "Y" or "R" circuit). Preferred for finished ceilings—no visible drain pipe needed. Separate Overflow Drain Line* (IMC 307.2.3.3): Second connection on coil/pan, piped independently to conspicuous termination. No trap.

Critical Details:

• Pan Material: Metal (galv/SS) or UL-listed plastic (IMC 307.2.3.1).
• Support: Pan fully supported; unit sits in pan, not on framing blocking drainage.
• Primary Drain Slope: 1/8"/ft min (IMC 307.2.2).
• Cleanout: Accessible cleanout on primary line near unit (IMC 307.2.2).
• Insulation: Insulate primary drain line in unconditioned attic to prevent sweating.

Pro Tip: Install a wet switch in the auxiliary pan (wired to break "Y" at air handler) AND run the pan drain to a conspicuous spot (soffit). Belt-and-suspenders. If using only a float switch in the primary line, ensure it's accessible for testing/cleaning.

Verify: Local amendments may mandate specific switch types or pan sizes. Pull permit; inspector will check pan, switch wiring, and termination point.