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Apprentice Q&A · #062

How do I properly strap flex duct to avoid "sag" and restricted airflow?

2nd YearFlex Duct & GrillesYELLOW · Check First

Support flex duct at intervals not exceeding 4 feet. The support straps must be at least 1\frac{1}{2} inches wide to distribute the weight across the jacket. * Keep the maximum allowable sag between hangers under \frac{1}{2} inch per foot of support span to prevent airflow choking.

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Plain-English answer

Support flex duct at intervals not exceeding 4 feet. The support straps must be at least 1\frac{1}{2} inches wide to distribute the weight across the jacket. * Keep the maximum allowable sag between hangers under \frac{1}{2} inch per foot of support span to prevent airflow choking.

Field checklist

Ask Foreman

Hey boss, I’m checking flex duct & grilles: How do I properly strap flex duct to avoid "sag" and restricted airflow? I found the likely issue and want to verify the next step before I lock it in. Do you want me to adjust it now or check the drawing/detail 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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