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SMACNA Duct question - duct shaft
We have a large concrete makeup air shaft on a project. The shaft will be lined with sheet metal. The contractor is saying that the duct will be 4" smaller on each side to account for flanges and other "space" that they need. We would therefore lose 8" of duct space in the shaft. Does SMACNA have an approved way to line the shaft with sheet metal to avoid the flanges and other space otherwise needed?