The common feature is the heating elements are mounted or backplare, braced to reduce vibration and the over temperature curoue are filled in a terminal enclose. The 100mm of insulation is fitted between the duct and terminals, 100mm mounting frame is used on medium(high) temp heaters to move the duct mounting flange to the duct wall. It iswidly used for heating air&gas, Finned elements are used for low and medium temp and tubular elements for high temp.

The heater should be interlocked with fan, and it may also be desirable to interlock with an air flow or differential pressure switch, To comply with NEC requiremengts, individual circuits are limited to 48 amps. Standard heaters are suitable for pressure up to. 3kg/cm2, sbove this pressure Circulation hearters should be used. The medium hearter air (or gas)form atmospheres to Max temp of 260C, The high temperature range is not more than 500C.