The heat diodes have essentially uni-directional heat transfer. The present research shows the analysis various types of gravitational heat diodes and investigation results for diode operating in evaporation-condensation cycle. The basic attention paid to heat transfer both in open and close diode mode. The model developed for diode ratio determination for gravitational evaporation-condensation device as the attitude of direct heat flow to opposite heat (low. The requirements for heat carrier, for thermal physics parameters of container material arc formulated for providing the diode ratio increasing. The numerical calculation results were compared to experimental data for various types of heat diodes.