Why does your windshield fogs up?

You may have a leaky heater core causing that condition. If you also smell coolant, you have a leaky heater core.

Look also at any water ingress around doors and Windows. This can cause misting when heat enters the vehicle i.e. when heating is on etc.

Also one big issue is people use polish based window cleaners or cloths with window cleaner on. This will help form misting of glass. if this is the case wash down with soap and water, dry with tissue.