Abstract: A heat exchanger device including a core having a stack of parallel heat-conductive plates which are formed with corrugations for channeling air between the plates, each plate being fabricated from a single sheet. The corrugations of successive plates are offset from each other for providing both separation and support of the plates with respect to each other. The heat exchanger is the combination of the core and a ventilation unit in a single housing for ventilating primary and secondary air through respectively alternating pairs of successive plates.