Abstract: Apparatus for generating heat, comprising a device for the electrochemical decomposition of water to generate hydrogen and oxygen, separate conduits for hydrogen and oxygen respectively, each one provided with a control device, and a device for mixing hydrogen and oxygen in a predetermined ratio, as well as a burner for the mixture. The apparatus is a unit in which the device for the electrochemical decomposition of the water is a tank with an anode compartment and a cathode compartment separated from each other by a wall which extends over essentially the entire height of the tank and has an opening adjacent the bottom of the tank and no higher than the lower end of the anode and/or cathode, which anode and cathode extend downwardly in each respective compartment.