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Apprentice answer

Why is a 45-degree elbow sweating at the heel after insulation

2nd YearInsulation, Liner & CondensationCheck first

Condensation usually means humid air is reaching cold metal through an air gap or broken vapor barrier. Dry it, tighten the wrap, and seal the vapor barrier continuously.

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Plain-English answer

The outside heel of a cold supply elbow sees strong temperature difference. If the insulation has a pocket, loose wrap, torn foil, or open seam, humid plenum air can reach the cold metal and sweat.

Dry the metal and insulation area, rewrap tight to the elbow shape, and seal the foil/vapor barrier completely. If water got into the insulation, replace wet material instead of taping over it.

Ask Foreman

The 45 elbow heel at [location] is sweating because the insulation/vapor barrier has a gap. I dried the area and found the break. Do you want the wrap replaced and resealed now?

Verify before acting

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

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