An FCU runs cold water through a coil in your ceiling void. It produces condensate that must drain away, and its pipework and valves must be insulated. Common failures: a drain pan that is blocked, cracked or wrongly sloped so it overflows; missing or wet insulation on the chilled-water pipes so they sweat along their length; and uninsulated valves dripping onto the ceiling. Any of these keeps the ceiling gypsum wet and growing mold.
Key takeaways
- FCUs make condensate that must drain; a blocked pan overflows into the ceiling.
- Bare or wet chilled-water pipe insulation sweats continuously.
- Uninsulated valves and unions are common drip points.
- This is usually a building/FM maintenance issue, not a tenant fix.
How an FCU causes damp
Chilled water (typically around 6–12 °C) runs through the FCU coil. Warm, humid air passing over that coil condenses, and the water collects in a drain pan and is piped to a drain. The supply and return pipes, valves and the pan itself are all cold surfaces that will sweat unless properly insulated. When the pan cannot drain, or insulation is missing or has become saturated, water ends up on the ceiling board above your rooms.
Signs it is the FCU
- Ceiling staining or a soft patch directly below an FCU or along the pipe route from it.
- Damp that appears or worsens whenever the AC is running and stops when it is off for a while.
- A brown tide-line ring on the ceiling that slowly enlarges.
- Musty smell from the ceiling void or the return-air grille.
What can be checked
An AC or FM technician can open the ceiling access panel and check: the drain pan for standing water, cracks or level; the condensate drain line for blockages and correct fall; the pipe insulation for gaps and saturation; and the valves and unions for sweating. They can also confirm the coil and filter are not so fouled that airflow and drainage are affected.
Who fixes it
In an apartment building this is normally the responsibility of building management or the FM contractor, because the FCU, its pipework and the ceiling void are building services. Report it in writing with photos and ask for the drain pan, drain line and insulation to be inspected — not just the ceiling repainted. See mold in a rented apartment.
Repainting an FCU-damaged ceiling without fixing the pan or insulation is a guaranteed repeat. Insist the mechanical cause is addressed.