Experiments on heat transfer and pressure drop in a triangular-channel specimen of a plastic heat exchanger are reported. The channel geometry was designed to cause the augmentation of near-wall mixing processes in air. Experiments were performed over a Reynolds number range of 400 to 4000. Enhancement of the heat-transfer coefficient on the gas side was used to compensate the overall heat-transfer coefficient for the low conductivity of the plastic. Within the same pumping power, the heat-transfer augmentation in a specimen of heat exchanger with triangular channels was found to be on the same level as a specimen with pin-fin internal geometry and microgrooved channels, but its construction was technologically simpler and remarkably cheaper.