The vent window looks like a really simple alternative to a heat exchanger. I would say that if you heat with electricity, Ie no flue, no exhaust air then there is no draw for the windows. If you are heating with a furnace or heater having a flue and the heater is off then the air flow could go the other way unless there is a flap of sorts to prevent that. For example at night the warm air inside at the level of the top of the window would be pulled into the area between the window segments as the air there cools and drops outside.
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