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Apprentice Q&A · #114

How do I test a welded grease duct system for leaks (light test vs. water test)?

3rd YearSpecialty DuctRED · Stop / Verify

The Light Test (Standard Rough-In): Pass an ultra-bright (10,000+ lumen) construction LED light bar slowly through the inside of the completely assembled, uninsulated duct run. A helper walks the dark exterior of the run checking for any pinpricks of light escaping through the welded seams. Any visible light leak indicates a structural weld failure that must be ground down and re-welded.

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Plain-English answer

The Light Test (Standard Rough-In): Pass an ultra-bright (10,000+ lumen) construction LED light bar slowly through the inside of the completely assembled, uninsulated duct run. A helper walks the dark exterior of the run checking for any pinpricks of light escaping through the welded seams. Any visible light leak indicates a structural weld failure that must be ground down and re-welded.

Field checklist

Ask Foreman

Hey boss, I’m on specialty duct and need verification before I touch this: How do I test a welded grease duct system for leaks (light test vs. water test)? Do you want me to stop here and check the approved detail, submittal, or inspector/manufacturer requirement first?

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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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