Measurement of air flows is an important task in many process monitoring systems. In applications like control of ventilation and air conditioning systems, robustness, ease of use, and cost are important issues calling for simple and effective sensor design. This paper investigates the use of commercial-off-the-shelf printed circuit board technologies for the fabrication of calorimetric flow sensors. Such sensors are known to be sensitive when being implemented using thin-film technology. The paper reviews the operation principle of thermal flow sensors and their performance in micromachined silicon technology for comparison. Subsequently, a similar design is introduced where heating and temperature sensing elements are made from standard copper traces on a flexible PCB substrate. Simulation studies demonstrate the basic viability of this approach, even if it might entail some performance penalties. First experimental data of sensor prototypes show that the repeatability of the PCB manufacturing processes is basically sufficient for using copper traces as sensors, but leaves also room for future improvement in both technology and sensor design.