Unlike the cement industry the conversion of furnaces of boilers with internal flues from oil/gas to coal has not reached beyond a few beginnings in the Federal Republic of Germany up to now. Such a changeover, however, will make it possible to reduce the fuel costs by about 25% and the expenditure for the necessary investments will be repaid within a very few years. Two examples how such a conversion of the furnace of internal flue boilers will proceed are given and the requirements and problems which crop up are discussed. Such conversions of furnaces would also be welcomed from the point of view of the entire economy of the Federal Republic contributing to the reduction of oil and natural gas imports and diminishing of the coal dumps which have increased again recently. The magnitude of the possible savings of fuel expenditure can be seen from two 12 t/h boilers in a brewery where such a conversion saved more than DM 400,000 per annum.