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Apprentice Q&A · #378

Why does a metal-to-metal duct connection at a louver sleeve whistle?

2nd YearGREEN · Standard CorrectionSleeve Gasket Omission

Short answer

Metal-to-metal sleeve joints leak. Pull the flange, clean the faces, add the approved gasket/sealant detail, and re-tighten evenly.

Field answer

A duct flange bolted to a louver sleeve can look solid but still leak if the gasket is missing. Under fan pressure, the gap becomes a whistle.

Verify the joint face, gasket, fastener spacing, and sleeve alignment. The recovery is to unbolt the joint enough to clean it, install the approved butyl/neoprene gasket or sealant system, then tighten evenly without twisting the sleeve.

What to check first

Do not do this

Do not smear mastic over the outside of a metal-to-metal flange leak if the missing gasket is inside the joint.

Why it matters

A missing gasket can waste air, make noise, and fail leakage/TAB checks.

Ask foreman

The duct-to-louver sleeve at [location] is whistling and appears bolted metal-to-metal. Do you want me to open the joint and add the approved gasket/sealant detail?

Text this wording

Related Field Rescue route

Open routeBack to Q&A

Final direction belongs to the foreman, approved drawings/specs, manufacturer instructions, pressure/material schedule, employer policy, and AHJ/code requirements.