The invention provides a method and a system for controlling floor heating or climate regulating systems with long time constants. According to the invention, a flow of a fluid is provided through the floor or through a similar medium with large thermal inertia. An induced heat is determined by adding up a plurality of differences between an inlet temperature of the fluid when it enters the medium and an outlet temperature of the fluid when it leaves the medium. The temperatures are sampled with a fixed sampling time and within a fixed period of time, and a corresponding change in temperature of the medium over the fixed period of time is determined. In the future, the temperature of that medium is controlled by use of a ratio between the induced heat and the change in temperature.