Why does a fan coil need a flexible connector at the duct connection?

A fan coil or fan-connected unit hard-piped to duct can transmit motor vibration. Add the approved flexible connector/isolation detail and make sure the duct is independently supported.

['Rotating equipment can send vibration straight into rigid ductwork if there is no break between the unit and the metal duct. That hum can travel into the ceiling grid and occupied space.', 'The fix is to install the project-approved flexible connector/canvas/isolation detail at the equipment connection, with enough slack and proper clamping/fastening. The duct still needs its own support; the flex connector should not carry weight or be stretched tight.']

Joints, TDC, Flanges & Connections 2nd Year GREEN

Stop if

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.

Check

Hard connections can spread motor hum, loosen joints, crack sealant, and create noise complaints after occupancy.

Steps

Confirm the vibration source is the unit, not loose ceiling, hangers, or duct rubbing.
Check whether a flexible connector/isolation detail is shown on the submittal/drawings.
Make sure ductwork is independently supported and not hanging from the unit collar.
Check connector material, slack, alignment, and access.
Recheck vibration/noise after startup.

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