A heater assembly is disclosed herein. The heater assembly may comprise a tubular body. The tubular body may include a graphite core disposed in a heating path. The graphite core may be coated with an overcoat layer. The tubular body may include slits that may cut-off heat transfer between portions of the tubular body. The heater assembly may have a configuration comprising a plurality of heating rungs having a predominant portion disposed substantially perpendicular to an upper surface of the heater so that the predominant portion is disposed vertically. The heater assembly may include a flange at a first end and a lip at a second end. The heater assembly configuration provides a heater that exhibits reduced thermal stress and/or reduced CTE mismatch stress particularly compared to other designs.