The temperature transients arising from instantaneous plane heat sources in a linear heat conductor are analyzed. The thermal conductivity and the specific heat of the conductor are assumed to be temperature independent. Two thermometers are fastened to the conductor. The thermometers possess heat capacity causing inert response. It is found that the position and strength of a heat source can be calculated from the first and second time integral of the observed transient temperature difference between the two thermometers. If the inertia parameter is large, the thermometer heat capacity can be derived from the response to a uniform short heat pulse. The method can be applied to problems of low‐temperature plastic deformation and superconductivity. An experimental example is discussed, in which instantaneous plane heat sources are generated by localized discontinuous tensile deformation at 4.2°K. The positions of the slipped zones and the amount of heat released during each slip are determined.