These are starting to catch on, as someone else said Heat Exchanger, but that's a more general concept and this is the thing you'd actually want https://en.wiki

These are starting to catch on, as someone else said Heat Exchanger, but that's a more general concept and this is the thing you'd actually want https://en.wikipedia.org/wiki/Energy_recovery_ventilation https://en.wikipedia.org/wiki/Energy_recovery_ventilation