Recently, coupled electromagnetic-reservoir simulators based on full numerical schemes have been developed using commercial software packages. However, simplified analytical and semi-analytical models can provide useful and quick insight of the complicated coupling between radio wave propagation and transport phenomena in heavy oil reservoirs. In this study, we developed simplified coupled EM-thermal models to emphasize on two important aspects of radio frequency heating process, near-field analysis and insulated antenna setups. It will be shown how much thermal error can be introduced when a proper full-wave analysis is not taken into account. We will also demonstrate the thermal advantage of applying an insulated antenna over a bare antenna when radio waves are used for heating purposes. Another key aspect of radio-frequency heating process is to consider dependency of electrical properties to thermal and water saturation conditions. This one is more difficult to verify analytically and it will be done in the second part of this study.