It is well known that heat is generated when an electric current passes through an electrical conductor. While various applications in our daily lives and industries utilize the heating of electronic conductors, little attention has been paid to the potential of ionic conductors for heating purposes. This is because of the 'inevitable' electrochemical reactions, which can result in unwanted electrolysis of conductors, corrosion of electrodes, and surface fouling. This paper reports the Joule heating of ionic conductors without electrochemical reactions. Electricity with a zero-phase frequency is employed to suppress the electrolysis of ionic conductors at high voltages. Demonstrations with various ionic conductors, both liquids and solids, show highly efficient energy conversion free of electrochemical reactions. This heating method is simple, direct, fast, clean, and uniform, and it has great potential in numerous industrial and household applications.