A frost-free membrane energy exchanger design model is developed combining the conventional ε−NTU method with a frost limit model. A concept of plate performance index is defined to evaluate the net energy saving ability. The frost-free design model and plate performance index are employed for a case study of single-family dwelling with an all-fresh-air air handling unit with a heat/energy recovery exchanger. The membrane energy exchanger, which is able to ensure frost-free operation without extra frost control strategies, is applicable to most cold climates for residential applications. The membrane energy exchanger has a significant energy saving potential compared to conventional plate heat exchangers. Preheating rather than enlarging the energy transfer area is recommended for severe cold climates.