Abstract: A gas flow monitor which includes a sensor composed of a pair of identical parallel wires to be positioned in spanning relation of the flow path of a duct and a heater to heat the length of one of the closely adjacent identical wires and wherein a voltage measuring device is provided to measure the voltage drop and hence the resistance across each of the wires which are energized by a constant current source and are in series with one another so that, upon comparison of the two, the effect of increased air flow through the duct will affect both wire lengths equally and the effect of any increase in air flow through the duct will have a net effect only of offering the resistance of the heated length of wire by reason of heat exchange between the heated wire.