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Apprentice answer

Why is a cold supply tap sweating above the ceiling

2nd YearInsulation, Liner & CondensationCheck first

Cold supply metal exposed to humid plenum air can sweat. Dry it, verify insulation/vapor barrier requirements, and wrap/seal it so humid air cannot reach the cold metal.

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Plain-English answer

Sweating duct is usually a vapor barrier problem. Cold supply air chills the metal skin; humid air touches it; water forms and drips onto ceiling tile, drywall, equipment, or finished space.

The correction is to stop the water damage, dry the surface, and install/repair the specified insulation and vapor barrier. The seams, corners, collars, and tap connections need to be sealed airtight on the vapor barrier side, not just wrapped loosely.

Field checklist

Ask Foreman

The supply tap at [location] is sweating and dripping. I dried the metal and checked missing insulation/vapor barrier. Do you want it wrapped/sealed per the insulation spec and nearby cold surfaces checked too?

Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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