A method and apparatus for measuring the flow velocity of a flowing fluid includes a positive temperature coefficient thermistor to be immersing within the flowing fluid in order to provide a measurement of the rate of heat dissipation of the thermistor produced by the flowing fluid, and thereby a measurement the flow velocity of the fluid. The positive temperature coefficient thermistor used has a resistance which increases sharply at the predetermined temperature at which electrical current is maintained in the thermistor such that the thermistor is self-controlled to maintain substantially the predetermined temperature, whereby the electrical current drawn by the thermistor is a measurement of the thermal load on the thermistor resulting from the thermal heat dissipation therefrom by the flowing fluid, and thereby a measurement of the flow velocity of the fluid. Various embodiments of the invention are described, including those for measuring heat flow in a centralized heating or air conditioning system, wind velocity and direction, and flow velocity in a wind tunnel.