Brooklyn thermostat

A window open in the dead of winter, as used by tenants of apartments with building-controlled heating (typically steam radiators), which presumably doubles as a basement blast-furnace and would otherwise boil the occupants alive. So-named for its prevalence in the NYC borough and similar metropolitan areas with many pre-war buildings.

"That open window ain't a 'waste of energy,' it's the Brooklyn thermostat, and I swear d'ya it's the only thing keepin' us all from becomin' kebabs!"