AC Dripping from Ceiling?

Water stains spreading across a ceiling or an active drip from above an attic air handler is a genuine emergency in Tampa Bay. The damage happens fast: drywall softens, insulation compresses, and mold can start growing within 24 to 48 hours in Florida’s humidity. Here are the four causes we find on these calls, ranked by frequency.

1. Clogged condensate drain line. This is the cause on the overwhelming majority of ceiling-drip calls in Tampa Bay. Your air handler pulls humidity out of the air and the resulting condensate water drains through a PVC line, typically out through the garage wall or to a floor drain. That drain line passes through the humid attic environment and algae grows inside it year-round in Florida’s climate. Once the line plugs, the drain pan inside the air handler fills up and overflows. In attic-mounted systems, that water has nowhere to go but down through the ceiling below.
2. Overflowed or damaged secondary drain pan. Code-compliant attic air handler installations include a secondary drain pan under the entire unit, a second line of defense if the primary drain clogs. That secondary pan also has a drain line, usually exiting at the eave or through a different exterior wall than the primary. If the secondary pan itself rusts through (common on units older than 10 years in Tampa’s humidity), or if its drain line also plugs, water overflows directly onto the attic floor and then through the ceiling below.

Florida Building Code Section 1411.3 (FBC Mechanical) requires that HVAC installations in attic spaces include a secondary condensate drain or overflow protection. This means either a secondary drain pan with its own independent drain line run to a visible exterior location (so you can see when the primary drain fails), or a float switch wired to shut down the air handler when water accumulates in the primary pan. Most Hillsborough County inspectors require both for attic-mounted horizontal systems. If your air handler is in the attic and was installed before 2007, it may predate the requirement and have neither a secondary pan drain to the exterior nor a float switch. Adding these to an existing installation does not require a new permit in Hillsborough County, but all work must be performed by a licensed CAC contractor. At home sale, inspectors flag the absence of secondary drain protection as a deficiency, and some buyers’ lenders require it corrected before closing.

• Every month (year-round): Pour one cup of distilled white vinegar into the condensate drain line access cap. Tampa’s heat and humidity grow algae in PVC drain lines faster than any other Florida climate zone. Vinegar prevents buildup without damaging the PVC or the float switch.
• Every spring (April before peak season): Have the drain line professionally flushed with a wet-vac and nitrogen blow. A line that flows in April can be fully blocked by July. One flush in spring prevents ceiling damage all summer.
• Every year: Inspect the primary drain pan for rust blisters. Tampa’s high humidity causes galvanized steel pans to rust from the inside out. A pan that looks fine from below can have pinhole rust through on the bottom. Replace any pan showing rust through.
• Every 3 to 5 years: Test the float switch by pouring water directly into the primary pan. The system should shut down within 30 seconds. If it does not, the switch is failed or wired incorrectly. A float switch that does not trip is not protecting your ceiling.
• After any ceiling water event: Check attic insulation above the drip location. Wet insulation holds moisture for weeks and can sustain mold growth even after the drain is fixed and the drywall appears dry. Replace saturated insulation rather than letting it dry in place.