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Apprentice answer

Why can a concentric reducer cause water pooling in round duct

3rd YearRound, Spiral & Flat Oval DuctCheck first

Use the fitting shape that keeps drainage moving. A bottom lip in a wet exhaust line can become a corrosion trap.

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Plain-English answer

A concentric reducer can create a dam at the bottom of a horizontal run. In humid exhaust or wash areas, that low pocket holds water and attacks seams.

Check flow direction, pitch, drain path, and whether the system should have an eccentric flat-bottom style fitting, drain detail, or revised route. Hold the change if it affects specified materials or listed exhaust construction.

Ask Foreman

The reducer at [location] is creating a bottom pocket that holds condensate. I checked slope and drain direction. Do you want an eccentric/flat-bottom fitting or revised drain detail?

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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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