Keeping a window slightly open will also help with your problem.
In our clod climate, I have leaned not to let the ''recirculation'' system on for an extended period of time. On ''recirc'', the inside (damp) air is being constantly recirculated which only make the problem wost. I use it 10-15 minutes when it is very cold than switch it off. The cold outside air is much drier than the inside hot/damp air.
it is also a good idea to clear the heater air intake (below the windshild wiper) of any snow. As it melts, water and damp air are sucked into the system.