Duct heaters are heat transferring devices which are an assembly of heating elements mounted in a frame or duct. Preferably used for non-pressurized air-heating systems, there are three types of duct heaters available: open coil, tubular or finned tubular heating elements that are either flanged or inserted in the duct. The individual elements are removable through the housing of the assembly, which eliminates the need to pull the complete heater from the ductwork. This reduces downtime costs because the heating elements can be replaced individually. Being the most easily adaptable heating solution, they are easily installed in applications requiring a wide range of temperature versus air flow combinations and offer greater reliability, energy efficiency, quicker response time and reduced infiltration from the air steam. Duct heaters can be equipped with a temperature control system and wired in various power configurations