Reliable information on the heat distribution inside biological tissues is essential for the planning and optimization of experiments which aim to study the effects of non-ionizing radiation (NIR). In electrodynamics, the finite-difference time-domain (FDTD) technique has become the dominant technique for radiofrequency dosimetry. In order to obtain the electromagnetic field and heat distributions within the same simulation run without changing discretization, a heat diffusion solver has been directly integrated into an advanced electrodynamic FDTD kernel. The implementation enables both coupled and sequential simulations. It also includes the ability to work with complex bodies and to accelerate heat diffusion. This paper emphasizes the importance of this combination in the field of NIR dosimetry. Two examples from this area are given: the validation of dosimetry with temperature probes and the estimation of the highest thermal load during bioexperiments.