A contract drawing labels a duct at 24 x 36 and shows 1" liner. What size should the duct be fabricated?

In this scenario, the duct measurement provided on the contract drawing is specified as 24 x 36 inches, with an additional instruction indicating the presence of a 1-inch liner. When lining a duct, the inner dimensions of the duct will be reduced by the thickness of the liner.

Specifically, if the duct is 24 inches wide and has a 1-inch liner on both sides, the effective inner width will be 24 inches minus 2 inches (1 inch on each side), resulting in an effective size of 22 inches. Similarly, for the height of 36 inches, the effective inner height becomes 36 inches minus 2 inches, resulting in an effective height of 34 inches.

However, when fabricating the ductwork, it is important to maintain the outer dimensions of the duct as specified in the contract, leading to the need to add the thickness of the liner to the original dimensions. Therefore, you add 2 inches to both the width and height to accommodate the liner.

Starting with the original dimensions of 24 inches by 36 inches, the recommended fabrication size of the duct takes these additional measurements into account, resulting in an outer dimension of 26 inches by 38 inches. This ensures that once