The gross theory of beta decay developed by Takahashi and Yamada has been applied to an estimation of nuclear decay heat of short-lived fission products, that is, to the average energies of emitted beta particles and gamma rays and the half-lives. For short-lived fission products for which no experimental information is available, calculations have been performed with the most probable value of a parameter Q00, which represents the energy of the lowest level actually fed by the beta transition. The results have been summarized in the form of several simple formulas, which are functions of the Q value and mass number of the nuclide in question. When the half-life is determined experimentally, the certainty of the calculated results for the average released energies can be improved by means of a search for the best Q00 value based on the measured half-life for each nuclide. Evaluation of confidence bands is also performed for the calculated results.