In models where thermal equilibrium is imposed the total amount of energy absorbed from the incident radiation field should balance the total emitted energy in lines and continua. This constraint is not automatically satisfied, since the algorithm for calculating heating and cooling rates is based on the assumption that each spatial zone is at most marginally optically thick. As a check the total energy absorbed and emitted from the radiation field is printed at the end of the log file, along with the fractional error in energy conservation. An error greater than a few percent indicates an inaccuracy in the model results which may significantly compromise emission line strengths, for example. Such models should propbably be rerun with smaller values of emult.