A gas-to-gas energy exchanger utilizing a commutator repetitively diverts a jet of a first pressurized gas between an energy exchange conduit and an exhaust outlet. Upon entering the energy exchange conduit, the first gas creates a pressure wave which traverses the conduit at sonic velocity and, in so doing, compresses a second gas in the conduit. The now pressurized second gas opens a first check valve and egresses through a primary outlet. When the first gas is diverted to the exhaust passage, a rarefaction wave is created in the energy exchange conduit and traverses the conduit at sonic velocity plus the velocity of the first gas still in the conduit. The energy exchange conduit length may be selected such that the rarefaction wave reaches the downstream end of the conduit before the previously entered slug of first gas to thereby prevent mixing of the first and second gases in the primary outlet; alternatively, the conduit length may be selected to permit any desired degree of such mixing. The rarefaction wave closes the first check valve and opens a second check valve which permits the second gas to enter the downstream end of the conduit. The rarefaction wave also reverses the flow direction of first fluid passed by the wave so that the first fluid is caused to flow back upstream in the conduit to be aspirated into the exhaust passage by the jet of first gas. The commutator is preferably a fluidic oscillator, but may be a mechanically driven device; in either case the frequency is selected to provide desired operation consistent with the conduit length. Two such commutators may be employed, operating in 180.degree. phase relation, so that a constant flow of the second gas may be provided from half cycle to half cycle.