To enable highly efficient operation of large scaled ventilation systems a continuous measured and well located air flow monitoring for control purposes and energy management is needed. The air flow monitoring solution is targeting low manufacturing cost as well as sufficient accuracy when operating near complex duct flows like pipe bends and tees. Therefore, a novel, low-cost, thermal air flow sensor, which takes non-uniform velocity profiles into account, is presented and characterized due to its application in heating, ventilation and air conditioning systems. Extensive numerical simulations and experimental investigations in an operating ventilation system show reasonable results and prove basic feasibility of the suggested novel sensor concept.