The pozzolanic reaction of nanosilica in contact with C3S was monitored via isothermal conduction calorimetry. Since that reaction is affected by heat, its variations with curing temperature (25, 40 and 65 °C) were also analysed. The findings showed that while C3S hydration was accelerated by both nSA and higher curing temperature, the former impacted the reaction more intensely. Moreover, the presence of nSA was observed to shorten the acceleration stage during C3S hydration, inducing earlier precipitation of portlandite and earlier C-S-H precipitation and nucleation.