Synthetic silica gels with six different effective diameters of nano-pores (3–30 nm) were loaded with n-hexadecane (cetane) after the elimination of adsorbed water. Kinetics of the solidification and melting of cetane was studied by differential scanning calorimetry (DSC) above the room temperature. Two thermodynamically different states of cetane were found in the samples: the free (bulk)-cetane state and the confined-cetane state. As suspected, the third state of cetane can be amorphous. This has been indicated by the small total transformation heat. The complex crystallization effect of cetane has been found to obey the nucleation-and-growth kinetics and also to depend on the dimensions of confining pores of silica gel. The melting of cetane seems to vary only with the average diameter of silica gel pores, which satisfies the Gibbs–Thompson relation. The presented results validate the applicability of the DSC technique for the porometry. The cetane-medium calibration curve for the silica gel nano-thermoporometry has been determined.