Underfloor heating, which is connectable to a first electrical energy source, having - a heating conductor device, with -- a first heating circuit (14.1) and a first power stage, -- at least one second heating circuit (14.2) with a second power stage, and/or -- further heating circuits (14.3) with further power stages, - a heating temperature setting unit for setting the setpoint temperature, - a temperature sensor for measuring the actual temperature, - a device for activating the heating conductor device on the basis of the respective values of the setpoint and actual temperatures, whereby - a single control apparatus with a control module is present and is designed as multistage controller and is connected between the first energy source and the heating device, wherein the heating temperature setting unit and the temperature sensor output their signals to the control apparatus and the control module activates or deactivates one or more power stages (L1, L2, L3) of the heating circuits (14.1, 14.2, 14.3) individually or in combination on the basis of the difference between the setpoint and actual values, - wherein - the control module is designed as a PI control module, which calculates in each case a control output on the basis of the control deviation, that is to say the difference between setpoint and actual temperature, the P component of said control output being dependent on the magnitude of the control deviation and the I component of said control output being dependent on the duration of the control deviation, and correspondingly actuates the individual heating circuits (14.1, 14.2, 14.3), - in addition, a second electrical energy source for the power stages (L1, L2, L3) of the heating circuits (14.1, 14.2, 14.3) is connectable to the control apparatus, - the first energy source is the usual power grid and the second energy source is designed as individual alternative energy source, for instance photovoltaic installation or wind turbine, - a logic switching unit is connected between the second energy source and control apparatus and outputs to the control apparatus a control signal relating to the respective present energy production of the second energy source and, in the event of sufficient energy production, enables the second energy source to supply energy to the heating conductor device. - a heating conductor device, with -- a first heating circuit (14.1) and a first power stage, -- at least one second heating circuit (14.2) with a second power stage, and/or -- further heating circuits (14.3) with further power stages, -- a first heating circuit (14.1) and a first power stage, -- at least one second heating circuit (14.2) with a second power stage, and/or -- further heating circuits (14.3) with further power stages, - a heating temperature setting unit for setting the setpoint temperature, - a temperature sensor for measuring the actual temperature, - a device for activating the heating conductor device on the basis of the respective values of the setpoint and actual temperatures, whereby - a single control apparatus with a control module is present and is designed as multistage controller and is connected between the first energy source and the heating device, wherein the heating temperature setting unit and the temperature sensor output their signals to the control apparatus and the control module activates or deactivates one or more power stages (L1, L2, L3) of the heating circuits (14.1, 14.2, 14.3) individually or in combination on the basis of the difference between the setpoint and actual values, - wherein - the control module is designed as a PI control module, which calculates in each case a control output on the basis of the control deviation, that is to say the difference between setpoint and actual temperature, the P component of said control output being dependent on the magnitude of the control deviation and the I component of said control output being dependent on the duration of the control deviation, and correspondingly actuates the individual heating circuits (14.1, 14.2, 14.3), - in addition, a second electrical energy source for the power stages (L1, L2, L3) of the heating circuits (14.1, 14.2, 14.3) is connectable to the control apparatus, - the first energy source is the usual power grid and the second energy source is designed as individual alternative energy source, for instance photovoltaic installation or wind turbine, - a logic switching unit is connected between the second energy source and control apparatus and outputs to the control apparatus a control signal relating to the respective present energy production of the second energy source and, in the event of sufficient energy production, enables the second energy source to supply energy to the heating conductor device.