Why is a cold supply tap sweating above the ceiling?

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.

['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.']

Stop if

• 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.

Check

• Condensation can ruin ceiling tiles, create mold concerns, damage finishes, and make the HVAC install look bad after turnover.

Steps

• Confirm the duct is cold supply and identify humidity source/space condition.
• Check whether insulation is missing, damaged, compressed, or open at seams/collars.
• Dry the metal before wrapping or sealing.
• Verify specified insulation type/R-value/vapor barrier detail.
• Check nearby diffusers, boots, and seams for more sweating.

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