> sick building syndrome A lot of that, at least in the US, is due to having houses built more tightly for insulation, which stopped the natural air exchange f

> sick building syndrome A lot of that, at least in the US, is due to having houses built more tightly for insulation, which stopped the natural air exchange from drafts that would normally occur. Now the building codes have been revised to mandate that a certain rate of air changes occurs even in houses, usually done using a heat exchanger: https://bcapcodes.org/tools/code-builder/residential/ventilation/ https://bcapcodes.org/tools/code-builder/residential/ventila...