The issues of energy demand and anthropogenic environmental change have not interested historians of Prussian towns as yet. One of the reasons for that is undoubtedly the scarcity of sources that would allow for a well-grounded analysis of the energy balance of particular towns. The purpose to the article is highlight the research value of the account book of the Old Town of Elblag from the years 1404-1414, which specifies in detail the expenses and revenues of the town council and its various offices. The author demonstrates that the source can be used to estimate energy consumption in the municipal trading and industrial establishments as well as the role of wood in the town's energy supply. The analysis concerned the number and location of local mills and the energy demand of local brickyards. The available data are not sufficient to estimate the consumption of fuel in households or in industrial facilities (brickyards, lime kilns, tar kilns). The data from the account book indicate that facilities of the latter kind were located not only in public buildings (the town hall, the cloth hall, the school, the town clerk's house) but also in sheds all over the town. The accounts preserved are not a sufficient basis to calculate the amount of wood and coal used to heat particular dwelling houses. It is known that at the beginning of the 15th c. the Old Town of Elblag had 362 houses and 289 sheds; there were also 483 sheds in the suburbs. The New Town of Elblag had 239 dwelling houses. The only indication in that respect is the systematic record of the yearly amount of coal and wood used to heat the town hall.