The ductwork material influences the energy use of the air distribution system. Attention should be paid to the roughness of the duct material; because of code requirements, most ductwork in the laboratory facility will be metal with smooth interior surfaces. However, flexible duct will usually be installed at the branch level to connect to diffusers. These lengths should be minimized because they increase pressure drop. Turning vanes with airfoil shapes should always be included in the ductwork turns. Extra consideration should be given to standard procedures for preventing duct leakage and to determining type and amount of insulation used. [Industrial Ventilation: A Manual of Recommended Practice - 24nd Edition, 2001]
