My heater works, but the windows fog up so fast and I never have passengers and as soon as I turn the heater off while being on full-blast, the windows start fogging up again. Is this perhaps because moist air from the outside is making its way inside through the doors? Weird question, but this fogging up thing has been going on forever and I'm sick of it.

Thanks!

 

Most likely you live in a moist area of the country or in a valley. Either you can put your windows all the way down to make the air temperature equal inside the car..or put the windows up and put the heater on(defogger)....if you do it in-between(cold outside with windows open & hot inside) then it'll just fog up again.

 

Winter is tough. When there's a lot of moisture in the car, it'll fog up like crazy. You either have to keep it super hot in the car, then blast the AC (defroster) on the windows to clear them, then shut it off completely and roll that way until it fogs up again... or start replacing every seal on the car.