The calculation of excess heat in electrochemical cells involves certain assumptions. Errors in these assumptions have been offered as non-nuclear explanations for excess heat.
One assumption made by Fleischmann and Pons is that the efficiency of electrolysis is nearly 100%, meaning nearly all the electricity applied to the cell resulted in electrolysis of water, with negligible resistive heating and substantially all the electrolysis product leaving the cell unchanged. This assumption gives the amount of energy expended converting liquid DO into gaseous D and O. The efficiency of electrolysis is less than one if hydrogen and oxygen recombine to a significant extent within the calorimeter. Several researchers have described potential mechanisms by which this process could occur and thereby account for excess heat in electrolysis experiments.
Another assumption is that heat loss from the calorimeter maintains the same relationship with measured temperature as found when calibrating the calorimeter. This assumption ceases to be accurate if the temperature distribution within the cell becomes significantly altered from the condition under which calibration measurements were made. This can happen, for example, if fluid circulation within the cell becomes significantly altered. Recombination of hydrogen and oxygen within the calorimeter would also alter the heat distribution and invalidate the calibration.