Watlow® Duct Heaters, LDH SERIES and D SERIES, Constructed of sturdy 0.430 in. (11 mm) diameter WATROD™ heating elements mounted to a 1/4 in. (6 mm) thick steel flange, duct heaters are easily adapted to many non-pressurized air-heating systems. They are easily installed in applications requiring a wide range of temperature versus air flow combinations. The modular duct heater offers increased reliability. The individual modules are removable through the housing of the assembly, which eliminates the need to pull the complete heater from the duct work. This reduces downtime costs because the heating elements can be replaced individually. Performance improvements include quicker response time and reduced infiltration from the air stream being heated into the electrical enclosure. Watlow® duct heaters offer advantages over gas or oil fired and open coil electric units.