I just crack my shield a lil bit every now and then. Or just hold yer breath haha

 

I think this is where those Arai-style DS helmets are even more of a benefit. Cracking the faceshield a tiny bit doesn't let enough air in to be a discomfort but really keeps that fog off the shield. On many of my cold morning starts down in Big Bend over the last 2 weeks, I loved my AFX37...Arai-style DS clone. I have to have a dirt-style visor, good breathability, but relative warmth. The ability to set these types of faceshields at any position is extremely valuable.

Also, and this may sound odd, I found from many years of horribly cold enduro morning starts that learning to breathe "down" helps tremendously. It takes a small conscious effort, but it helps.

 

+1 ^
And, my AFX39 has a number of adjustable vents that provide good ventilation when you need it. I'll bet TNC's 37 does too.

 

I need to get me one of those AFX-39's

 

I have a Fly Racing Trekker helmet. Its a DS type motocross helmet. I love it. Lots of vents and has a Faceshield on it. Cheaper than an Arai too. Check them out, I highly recommend them.