To perform a measurement compliant with the 1st BImSchV, the combustion air in the intake area of the heating system must be recorded. For this purpose, temperature sensors are required, which can be attached with a magnet or cone in or on the intake opening of the system. So-called T-room sticks, which are attached directly to the measuring device and record the room temperature there, are widely used – but not compliant with the 1st BImSchV. If the temperature there differs from the intake air temperature, errors can occur in the measurement of exhaust gas loss. Ultimately, practicality and the required accuracy determine the use of T-room sticks / T-room sensors.