Open coil heating elements have open circuits consisting of coiled resistance wire (usually Ni- Chrome or FeCrAl) fixed onto a supporting element that heat the medium directly. Termed as the most efficient and versatile while also the most economically feasible solution for heating, these elements have fast heat up times that improve efficiency and have been designed for low maintenance and inexpensive replacement parts. When an electrical current is applied to the wire, it gives off heat. The wire is connected to the control panel which regulates the amount of heat provided by the electric heater and fills the tunnel of the air handling unit. Because of the low mass and fast response time, SSR or SCR switching devices are advisable.