Swamp Coolers: The Rooftop Leak You Meet as a Ceiling Stain

Evaporative coolers are a beloved, cheap way to cool desert air — and a water appliance parked on your roof, fed by a pressurized line, running all summer. When one leaks, gravity does the rest: attic insulation, ceiling drywall, then the living room.

Where they fail

• Float valve sticks: the pan overfills and overflows — continuously, until noticed. The classic failure.
• Supply line and fittings: the small copper or poly line up the roof bakes in UV and heat; pinholes and split fittings drip onto the roof or into the penetration.
• Pan corrosion: mineral-rich water eats the reservoir pan; rust streaks below the unit are the warning.
• Winterization skipped: lines left charged through a freeze split quietly, and announce themselves at spring startup.
• Overflow/drain line clogs: mineral scale blocks the relief path, so excess water finds its own.

The signs inside the house

A spreading ceiling stain — often ringed brown from dissolved minerals — sagging drywall, or a musty smell in one room during cooler season. By the time drywall stains, the insulation above it has usually been wet for a while: check the attic, not just the ceiling, and treat the mold clock (24–48 hours on wet materials) as already running.

The two five-minute checks per season

1. Spring startup: before first run — inspect the supply line end to end, watch a full fill cycle to confirm the float shuts off, confirm the overflow drain flows, and look at the roof surface around the unit for staining from winter.
2. Fall shutdown: shut the supply valve, drain the line and pan, and disconnect per the unit's manual. Most spring leak stories were written the previous November.

If the ceiling's already wet

Stop the supply at the valve, document the damage, and treat it like any interior water loss: assessment with moisture readings, removal of soaked insulation, drying of the ceiling assembly before repair. Insurance treatment follows the usual split — a sudden failure is typically covered, a long-running drip with old staining gets the gradual-damage argument (claim guide).