Latent heat of a temperature-dependent cubic-quartic Landau transition ($L=c(1-\gamma )(T^{\ast }{)}^2({\varphi }^{\ast }{)}^2$)

At an equilibrium minimum, $d{F}_{\min }/dT={\partial }_{T}F$ because ${\partial }_{\varphi }F=0$. For $0<\gamma <1$, the entropy decrease at coexistence is $S_0-S_{+}=c(1-\gamma )T^{\ast }({\varphi }^{\ast }{)}^2$. Multiplying by $T^{\ast }$ gives the positive latent heat released on cooling. The units are total heat or heat density according to the normalization of $F$.