Or open windows, but outside's cold in many places this time of the year. Energy recovery ventilators run stale outgoing air through a heatsink to pre-heat inco

Or open windows, but outside's cold in many places this time of the year. Energy recovery ventilators run stale outgoing air through a heatsink to pre-heat incoming fresh air to save heating costs. Sounds BS but it's a well established and widely used thing.