A method for heating or cooling a carbon containing reducing gas having a carbon monoxide content of at least 0.5 vol %, wherein the gas is heated to a temperature of at least 400° C. or wherein the gas is cooled from a temperature exceeding 400° C., wherein the gas is passed along a surface of a heating or cooling unit having a heat conductive metal or metal alloy body and a protective layer, which protective layer provides said surface, and which protective layer is made from a coating composition including colloidal amorphous silicate and crystalline oxide particles.