Results of numerical simulation of thermal regimes of heat pipeline in conditions of evaporation and moisture diffusion in moistening isolation were completed. Values of heat losses of heat pipelines insulation in conditions of evaporation and moisture diffusion in moistening isolation were established. Contribution of evaporation effect to total heat losses and need to consider volume fractions of water and steam into the structure of thermal insulation in calculation of effective thermal conductivity were shown. Nonstationarity of heat and mass transfer in conditions of considered problem can be ignored.