GOTONE- It's nice to be able to get out of the cold. But a man made heat source means you have limited supply and if you're cold, you are not dressed properly for the environment you are in. Cold weather survival is not a game of chance.  My advice is to invest in clothing, including boots, gloves and hat's. Your head is the human body's biggest heat exchanger- you lose massive amounts of body heat from your head because of the the large amount of blood vessels covering the outside of your skull. Ever wonder why a head cut bleeds like stuck hog! Get caught w/o a good hat & you can be in real trouble. All those old mountain men didn't wear the big furry hat's as a fashion statement.. As for clothing - layers of the right type of clothing that can be removed and put on or dried out as needed is the answer. Really good boot's- frozen feet are no joke if the rest of you is warm- extra sox- gloves etc. Ultimately it's what makes for survival of the fittest.

What happens when your manmade heat source fails or it turns into a unexpected raging blizzard where you can't find your way and your man made fuel supply runs out?  I alway's carry a flint & steel(even in my boat), plus I know how use it and how to find dry tinder and fire materials and how to use what mother nature provides to survive.  I also carry some survival food in my pockets or in the boat. High energy/calories to replenish the old human furnace. These are not snacks for the trip- but something that I fully intend to bring back w/ me.

Have you ever seen someone going into hypothermia in a cold rainstorm? I have, and the really bad part is they didn't think anything was wrong. They were just losing control and no one else recognised the symptom's. In the other extreme I've camped on the open Mississippi river ice overnight by myself w/o a tent or ice shanty for shelter in -20 below weather (that wasn't the windchill either). Why? I wanted to be there for the early morning northern & panfish bite! But I also knew what I needed to make it a safe adventure. It was awesome lying on the ice & watching the star's overhead. 

I know this really doesn't answer your fundamental question- but I hope that neither you or anyone else on MF  bet your life on a man made heat source.  I also carry an emergency tarp, even in the boat- One those little foil emergency blanket packs could mean your survival. Your worst enemy is being wet or cold w/ wind bowing on you. Learn to use what mother nature provides as your backup plan.

Al Warner

"All Water is Zalt Water"

http://www.zaltnad.com