Turned on car heater and windows fogged up.?

Well the cause is moisture in the cabin.

Try letting a window cracked open over night and see if the problem persists in the morning.

If that doesn't do it...

Do you smell anything when the defrost is on? A sweet smell? Is there a slight residue of an oily substance on the inside of your windshield? If so, you may have a small leak in you heater core. The heater core is a small radiator like baffle under your dash. The engine coolant (runs hot) through the heater core. A blower pushes air through the heater core and you get heat. However if the core has a leak (could be a small pin hole leak) you will get vapors from it onto your windshield. I am kind of leaning this way from what you described.

Or the coolant could be leaking within the lines connecting the heater core. If so, this could cause the same symptom that you describe.

Now the fix... obviously you can take the car to a mechanic and have them replace the core or the lines. This is an expensive procedure.

Are you keeping the car? If so, replacement is the best bet.

A cheaper fix... if you go to an Auto Zone or similar store, you can purchase a can of radiator stop leak. Place this into your radiator, not in the overflow tank. Put it right in the radiator by removing the radiator cap. Do so when the car engine is cool or cold. Careful not to do this if the engine is hot because there is pressure built up and you could burn yourself.

If there is a small leak, it (Stop Leak) will stop it and it will be your least expensive way of fixing the problem. No more fog!

LOL, that normal... Just leave the heater running for another 3 mins or so, and the they will clear.

When a cold windshield or window has hot air blown on it, it will fog and possibly frost, but within 2 mins the window will become the same temperature of the air blowing on it. THen the window will evaporate the fog and frost, and you will be able to see out of it easily. However, your heater must be really warm, let your car idle with the heater on blowing out of the vents under the windsheild. This will allow the windshield to melt any ice on the other side too.

Suggest that it will do that if your heater air intake,which is usually located underneath the windshield, is full of snow or ice. Suggest to keep it clear before starting heater and you should be good to go. Suggest to roll down the window a bit until the heater warmth kicks in,this can usually drive off the moisture. Another cause can be a leaking heater core,if this is the case you may see moisture on the floorboards ,passenger side.

Turn on the AC. I know it sounds strange, but hot air actually holds more water. The Air Conditioner takes water out of the air, and will clear up the window, especially on defrost setting. It's a good idea to use the AC for at least ten minutes a month in the winter anyway, to keep it lubricated and not just sitting there for months.