Different logic gates like MV, NOT, AOI, NNI etc. under QCA nanotechnology are introduced. NNI gate is highly effective regarding space and speed consideration. In earlier work, realizing symmetric functions in binary reversible logic is studied. In that, 2-inputs and 2-outputs AND-NAND and OR-NOR cells are designed. Ultimately a general equation for the minimum number of gates required to an arbitrary number of input variables causing synthesis of symmetric function is achieved. In current paper, the author compare the heat dissipation due to the garbage outputs for designing different combinational digital circuits with the help of symmetric functions realized circuits.