Interfacial instabilities play an important role in the development of critical heat flux models. For example, the critical heat flux models for pool boiling on infinite horizontal surfaces are formulated with the aid of Rayleigh-Taylor, Kelvin-Helmholtz, and Plateau-Rayleigh instabilities for inviscid fluids. Hence, the effect of fluid viscosities is usually not included in existing models. In this study, the interfacial instabilities based on the viscous potential theory are incorporated into two representative models: a hydrodynamic model and a macrolayer dryout model. The circular jet and Kelvin-Helmholtz instabilities for viscous potential flows are utilized. The viscous potential flow approach permits a velocity slip at the interface, but it includes the effect of the viscous normal pressure. These treatments are consistent with the fact that the interface waves are induced more by pressure than by shear force. The revised models based on the viscous potential theory show better predictions. Finally, a multiplier is proposed to account for the effect of the fluid viscosities. If the value of the critical heat flux is known at atmospheric pressure, the critical heat flux at different pressures can be estimated more accurately by the multiplier. (C) 2015 Elsevier Ltd. All rights reserved.