[zaroth]

It’s call “make-up air”.

Usually installed in the return air duct if you have a furnace, they put in a ~6” duct running from the air return to the outside world, with an electric baffle.

Two wires (like thermostat control wire) are run from vent to the baffle. All the big vents have a place where you can plug in to sense when the vent is turned on. Fancier models will have slower speeds that don’t trigger the baffle to open, and only open it at higher speeds.

I got a really powerful range hood. It has 3 speeds but I wish it had a fourth even slower/quieter one because even on minimum it’s pretty loud. So for example if I’m baking in the gas oven, I’d love to have a lower setting that could just ventilate a little without being loud.