  With a generic model for the electron-phonon spectral density, two simple
expressions are derived to estimate the transition temperature and
gap-to-temperature ratio in conventional superconductors. They entail that on
average the numerical value of the phonon exchange factor, $\lambda$, is
limited to 2.67, so that room temperature superconductivity may be attained
only with a Debye temperature of about 1800 K or higher, in materials that may
or may not involve hydrogen. They also show that a Be-Pb alloy may become a
superconductor at $\sim$44 K.
