Abstract The heat transfer of an air-to-air heat pipe heat exchanger (HPHEX) with counter flow and a high-temperature range was modeled. The HPHEX was constructed from sodium-stainless steel (STS) heat pipes (HPs) using a staggered configuration. The thermal numerical model was developed by the nodal approach, and the junction temperature and thermal resistance of the HP and heat transfer fluid of each row were defined. Surface-to-surface radiant heat transfer was applied to each row of the liquid metal HPHEX. The cold-side inlet air temperature was determined by iteration to converge to the minimum operating temperature of the sodium HP. The cold-side inlet velocity and position of the common wall were considered as the main variables in evaluating the performance of the liquid metal HPHEX, and their effects on the temperature distribution, effectiveness, heat transfer rate of each row were investigated. The proposed row-by-row heat transfer model is useful for understanding the temperature distribution of each row and can be used to predict the cold-side inlet temperature of a liquid metal HPHEX with counter flow. The recovery heat and effectiveness of the heat exchanger were calculated for various configurations and operating conditions. The simulation results agreed with experimental data to within 5% error for normal operation of the heat pipes, and within 11% error when the minimum temperature was lower than could allow normal operation of the sodium heat pipes.