It is often suggested that heat flow in the incoming plate at subduction zones is lower than expected for crust of that age due to increased hydrothermal circulation from flexure (extending about 300 km seaward of the trench) and faulting (observed starting about 50--75 seaward of the trench). Testing this suggestion using global heat flow data shows no significant difference between heat flow near the trench and the global means for the same age crust. However, on average, heat flow in the overriding plate is about 60% of that in the incoming plate.