Comment by jonstewart

One of the big trends in green/sustainable building is creating relatively air tight buildings in order to cut down on heating and cooling costs (see: Passiv Haus, Passive House, Pretty Good House). In order to do that, though, mechanical ventilation is needed. As a result, Heat-Recovery Ventilation & Enthalpy-Recovery Ventilation residential units can be installed for only $2k-$4K. Seems like a worthwhile investment (for when it’s not convenient or possible to open a window).