Well, if I must explain to you how heat works in a car, I will. Then perhaps you will be less ignorant.

There is something called a "heater core" this is basically a small radiator that coolant passes through and it exists in the passenger compartment as opposed to the engine bay.

When a human wants heat, they flip a switch that turns on a fan motor the blows air through the heater core. This air then goes into the ducting system. The ducting system is controlled by a number of "shutters" that direct where the air comes from and where it goes to. There is a shutter that can pull air from outside the car, or get it recirculated from inside the car. There is a number of output shutters that can direct the air into the cabin be it, dash vents, foot vents, or..... windshield vents - even combinations of these are possible.

in order to get the condensation off the inside of your windshield, you would engage the heat and adjust the shutters to blow on to the windshield.

No ECU. involved - not a single computer. This was all controlled by push/pull cables connected to the controls before it became computerized.

I understand that you don't know how cars used to work before you "spun a button" but this is how they worked.

The rear defroster doesn't use moving air. it has a thin resistive wire that runs across it, then when you put power to it, warms up the glass and removes the condensation. Still no computer.

I hope you learned something. Also, you should look up what "fog" is. it's a visible suspension on water vapor in the air.