Rooftop Unit Water Leaks? 8 Common Leak Points to Inspect
Water around a commercial rooftop HVAC unit doesn't always mean the unit itself is leaking. A clogged condensate drain, failed roof flashing, or rain entering through a damaged cabinet seal can produce similar symptoms—but each requires a different repair.
For HVAC service technicians and commercial building maintenance teams, the first step is to identify when the leak occurs, where the water appears, and whether it originates inside the RTU or around the roof penetration.
Where to inspect: Beneath the evaporator coil.
A cracked, corroded, obstructed, or improperly pitched condensate drain pan can allow water to overflow into the unit base or ductwork.
What to check:
Next step: Clear the obstruction, verify drainage, and repair or replace a damaged pan according to the manufacturer's requirements.
Where to inspect: The drain connection and external condensate piping.
A blocked drain line, improperly sized trap, or missing or dry trap can prevent condensate from draining correctly. On draw-through units, negative pressure at the drain connection can interfere with drainage when the trap is incorrectly designed.
What to check:
Next step: Clean and flush the drain, verify the trap configuration against the unit's installation manual, prime it as specified, and confirm that water drains freely during operation.
Where to inspect: The evaporator coil, filter section, and condensate pan.
A frozen evaporator coil can release more water than the drain system can handle when the ice melts. Restricted airflow, dirty filters, coil fouling, or a refrigerant-related problem may contribute to coil icing.
What to check:
Next step: Correct airflow restrictions and investigate the cause of freezing before returning the unit to normal operation. Check refrigerant conditions using the manufacturer's diagnostic procedure if indicated.
Where to inspect: Any installed condensate pump, auxiliary pan, float switch, and associated piping.
Not every rooftop unit uses a condensate pump or auxiliary drain pan. Where these components are installed, a failed pump, blocked discharge line, or malfunctioning float switch can allow water to accumulate and overflow.
What to check:
Next step: Restore proper drainage, test the float switch and safety controls, and confirm that the system responds correctly to a high-water condition.
Where to inspect: Service doors, access panels, cabinet joints, and fastener locations.
Damaged gaskets, loose panel fasteners, or deteriorated sealant can allow wind-driven rain to enter the cabinet. Water appearing near an access panel does not necessarily mean that the panel itself is the original entry point.
What to check:
Next step: Replace damaged gaskets, secure panels, and restore seals using manufacturer-approved materials. Confirm that cabinet drainage openings remain unobstructed.
Where to inspect: The interface between the rooftop unit and its supporting roof curb.
A deteriorated gasket or failed seal at this interface can allow rainwater to enter the building around the unit base. Improper curb alignment or installation can also contribute to water intrusion.
What to check:
Next step: Verify curb alignment and the unit's approved sealing details. Repair the interface according to the equipment manufacturer's instructions and coordinate with a qualified roofing contractor when necessary.
Where to inspect: Roof penetrations, flashing, membrane seams, and the area surrounding the unit.
Sometimes the RTU is blamed for a roof leak that originates several feet away. Damaged flashing, punctured roofing membranes, failed seams, or ponding water can allow moisture to travel beneath the roof surface before appearing inside the building.
What to check:
Next step: Document the suspected entry point and coordinate repairs with a qualified commercial roofing professional. Avoid applying sealant indiscriminately, which can conceal the source or interfere with the roofing system.
Where to inspect: The outdoor-air intake, economizer assembly, hood, and associated cabinet penetrations.
Wind-driven rain can enter through damaged weather seals, improperly installed hoods, or compromised intake components. Water may then collect in the cabinet and travel to a location far from the actual entry point.
What to check:
Next step: Inspect the assembly against the manufacturer's installation details and restore damaged seals or components. Verify that the intended drainage paths remain clear.
|
Observed symptom |
First areas to inspect |
|
Water appears during cooling operation |
Drain pan, drain line, P-trap |
|
Water appears after the unit shuts down |
Coil icing and condensate drainage |
|
Water appears during or after rainfall |
Roof flashing, curb seal, cabinet seals |
|
Water appears during wind-driven rain |
Outdoor-air hood, access panels, roof details |
|
Water enters the supply duct |
Drain pan, internal condensate overflow, unit-specific drainage paths |
|
Water persists after drain cleaning |
Verify trap design, airflow, and possible roof or cabinet intrusion |
These are diagnostic starting points, not definitive diagnoses. Water can travel inside the cabinet or roof assembly, so the visible drip location may be different from the source.
After identifying and correcting the cause:
🔍Confirm that the condensate drain and trap operate as designed.
🔍Check repaired connections, seals, and drainage paths for leakage.
🔍Inspect the surrounding roof area for unresolved water intrusion.
🔍Run the unit through an appropriate operating check and verify that water is draining normally.
🔍Document the root cause, corrective action, and any follow-up roofing work required.
Important: Follow the specific RTU installation and service manual, applicable electrical safety procedures, and local requirements. Roof access and work at height should be performed using appropriate fall protection.
For recurring leaks, documenting rainfall conditions, operating mode, and the precise location of the first visible water can help distinguish a drainage fault from a building-envelope problem—and prevent repeat service calls.
