During the winter 1979/80 a biogas plant located on an average sized dairy farm was monitored with respect to its heat requirements. The results showed that the energy consumption was higher than the energy content of the biogas produced. A comparison of the data collected with the calculated heat losses indicated strongly that substantial amounts of heat were lost through heat bridges. These losses could be visualised with thermography. Additional thermography determinations at other biogas plants showed that the most critical area of insulation was the overflow from the digester to the storage tank.