Front Windshield fogging problem

Hi all. I'm having this problem, whenever I start the car late at night I get alot of window fogging in my front windshield. This happens if I have my a/c off. It is annoying lol. Everytime I get out of class and I step on the gas almost all the windshield fogs up. I can feel that the hot air is coming from the front heater dash vent.

What I end up doing is putting the a/c on cold and switching it to heater vent for a few mins until the fogging is gone. This just started happening a few weeks ago. I'm thinking that maybe I have problem with the gate that opens and closes the heater vent or maybe a vacum leak. I kinda looked underneath the dash for a broken hose or an airleak but haven't seen or one yet. Any suggestions or ideas? Thank you.

that's usually a sign of a bad heater core.

Bad like leaking? Because I'm not smelling any antifreeze.

it takes very little heater core leakage to do this. Check clamps under hood first. It may be letting a drop run in. Then it's go to the core next. Or maybe your carpet has moisture under it. It will come out after sitting with the windows up. Maybe a spilled coke? Check all this first. nobuddie

sounds like a heater core to me, or a plugged drain tube. normally there is a rubber down tube on the firewall to let moisture out of the heater core area, so it could be leaking but just draining unto the ground not the floorboards.

you know, my geo has always fogged the windows. I have thought it is because the car is so small inside. I can turn on the AC for a minute and ity's fixxed. c