Stability of elements require determination of their dimension, such that the resulting displacement under static or thermal loads are acceptable. Those elements have to resist the applied loads so that the structure or any element does not loss constancy. The most important criteria for stability is represented via element curvature under the influence of load, that load is of any type or in any position. Therefor this paper presents derivation of a theoretical equation to calculate the deflection generated from heating variation between the top and bottom surface of simple steel beam, by means of heating transfer expression.