Total heat, E_h, generated per an accreted baryon in a layer from the star surface to a given density, as function of mass density ρ, according to the models of Haensel & Zdunik (2008) (HZ’08, dot-dashed red line) and Fantina et al. (2018) (F+18, solid blue line). The gaps in the lines correspond to the density discontinuities at the phase boundaries. The dashed green line without gaps shows a smooth analytical version of the model HZ’08, suggested by Chaikin et al. (2018, CKY). The vertical dotted lines mark the ρ values corresponding to four masses of accreted material, from 10⁻⁵ M_⊙ to 10⁻² M_⊙, labeled near these lines, for a neutron star with gravitational mass M = 1.4 M_⊙ and radius R = 12.6 km. The inset shows a zoom to the low-density region.