Device and method for providing useful heat and use of a heat plant

The device (1) comprises a heat generating energy unit (5) for providing usable heat (3) and electrical energy. A combined heat and power machine (6) is provided, which is supplied with a portion of the heat, such that usable heat is produced from the heat supplied to the combined heat and power machine. The heat comprises waste heat (7), which is generated when providing usable heat and electrical energy or when conveying usable heat. The waste heat is supplied to the combined heat and power machine.