Fogged Up Windows

Happy Holidays To Everyone!
I have a 1997 Volkswagen Jetta, V6, with 127,000 miles. Having a fogged up windows issue for some reason or another! Has anyone on the forum has this problem before? If so, how did you resolve it? Thus far, found via searching the internet that the problem could be a leaking heater core. I will check that later today. However, if the heater core was leaking shouldn't I be smelling anti-freeze. I will check the floor on passenger side to see if it's wet. Or could the problem be a bad thermostat? It appears the heater isn't getting that hot for some reason or another. Course, I guess that could be due to a leaking heater core ha! Appreciate any suggestions or recommendations! Take Care!

Could also be rain water leaking in this. The water can hide under the carpets undetected for ages. Lift the carpets up to have a good look (just a corner in several places should be enough)
Also might sound silly but make sure your not carrying lots of wet gear fishing stuff etc.

Thanks for responding! I had my daughter feel the carpet on the passenger side floor and she said it wasn't wet. I will check beneath the carpet further to confirm your statement. This morning, the dang thing didn't have fogged windows. Course, it was in a garage all night which may be the reason for that. If the carpet isn't wet beneath, what else could be the problem? The airflow from the vents are fine when the control know is set to defrost. I'm thinking the thermostat may be faulty although the car does has heat but it isn't getting hot enough to run you out of it. Course, right now the temp here is in the 20s and below! Appreciate your thoughts! Thanks again! Any other comments are welcome.

Could also be rain water leaking in this. The water can hide under the carpets undetected for ages. Lift the carpets up to have a good look (just a corner in several places should be enough)
Also might sound silly but make sure your not carrying lots of wet gear fishing stuff etc.