Gas permeation processes are often evaluated without considering concentration polarization effects. This is due to the assumption that gas diffusion coefficients are large enough to immediately compensate any concentration differences. However recent studies revealed that this assumption do not hold for systems comprising water vapor and air. Here the combination of high permeance and selectivity causes a limitation of mass transfer by the built up of a concentration boundary layer. A system most likely affected by such limitations is what we call a membrane based enthalpy exchanger. Due to simultaneous heat transfer the stagnant layer is expected to have a tremendous impact on overall performance. Mass and heat recovery will be improved, if membrane spacers are applied. However the application of such spacers is typically accompanied by an increase in pressure loss. In order to evaluate the economic benefit different module prototypes were assembled. Some of the systems comprised spacers others not. Comparing the experimental data of both configurations revealed a positive impact of membrane spacers on heat and mass transfer properties. In a subsequent case study module efficiency was evaluated using climate data of two locations, one in Central Europe and one in Canada. Even though the additional pressure loss reduced total savings, spacers accounted for a positive net balance in both cases. (C) 2016 Published by Elsevier B.V.