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Apprentice answer

Why can blocking the back of a fresh-air intake louver starve the system

2nd YearRoof Curbs, Louvers & Exterior AirStop / get direction

A louver needs an open air path behind it. If another trade covers the opening, stop the cover-up and get the obstruction removed or redesigned before startup.

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Plain-English answer

A fresh-air louver can look fine from the outside while being completely blocked behind the screen. If the sheathing, siding, or backing board covers the air path, the air handler can be starved and the building can pull negative pressure.

Verify the louver has an open path behind the full active area shown on the mechanical drawings. Stop cover-up work, document the obstruction, and coordinate the cutout or framing correction. Do not start the fan against a blocked louver.

Ask Foreman

The intake louver at [location] is blocked behind the bird screen by [material/trade]. I verified the face is not open to the plenum. Do you want this held for the GC/siding crew to cut the opening clear?

Verify before acting

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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