This paper considers the problem of constrained tracking the timevarying room impulse response of a source/microphone pair. The constraint which is used to improve the performance stems from the energy conservation that has to hold for real-world impulse responses. We consider three different recursive estimators and compare their performance with the recursive weighted least squares algorithm which does not take the constraint into account. The simulation results show that exploiting this constraint decreases the mean squared error and is thus interesting for applications, especially in the low SNR regime.