  Gas planets in close proximity to their host stars experience
photoevaporative mass loss. The energy-limited escape concept is generally used
to derive estimates for the planetary mass-loss rates. Our photoionization
hydrodynamics simulations of the thermospheres of hot gas planets show that the
energy-limited escape concept is valid only for planets with a gravitational
potential lower than $\log_\mathrm{10}\left( -\Phi_{\mathrm{G}}\right) <
13.11~$erg$\,$g$^{-1}$ because in these planets the radiative energy input is
efficiently used to drive the planetary wind. Massive and compact planets with
$\log_\mathrm{10}\left( -\Phi_{\mathrm{G}}\right) \gtrsim 13.6~$erg$\,$g$^{-1}$
exhibit more tightly bound atmospheres in which the complete radiative energy
input is re-emitted through hydrogen Ly$\alpha$ and free-free emission. These
planets therefore host hydrodynamically stable thermospheres. Between these two
extremes the strength of the planetary winds rapidly declines as a result of a
decreasing heating efficiency. Small planets undergo enhanced evaporation
because they host expanded atmospheres that expose a larger surface to the
stellar irradiation. We present scaling laws for the heating efficiency and the
expansion radius that depend on the gravitational potential and irradiation
level of the planet. The resulting revised energy-limited escape concept can be
used to derive estimates for the mass-loss rates of super-Earth-sized planets
as well as massive hot Jupiters with hydrogen-dominated atmospheres.
