We present a method to characterize the temperature dynamics of miniaturized thermal IR sources. The method circumvents the limitations of current IR photodetectors, by relying only on an electrical measurement rather than on optical detection. Thus, it enables the characterization of the light emission of IR sources over their full operation frequency range. Moreover, we develop a model of thermal IR sources allowing simulations of their thermal and electrical behavior. By combining measurements and modeling, we achieve a comprehensive characterization of a Pt nanowire IR source: the reference resistance R0 = 17.7Ω, the TCR α = 2.0 × 10-3 K-1, the thermal mass C = 2.7 × 10-14 J/K, and the thermal conductance G = 1.3 × 10-6 W/K. The thermal time constant could not be measured, because of the frequency limitation of our setup. However, the operation of the source has been tested and proved to function up to 1 MHz, indicating that the thermal time constant of the source is smaller than 1 μs.