Huntinglife is on the right track.
I use a medium sized cylinder stove to heat my 14x16 tent. It's fairly easy to regulate the heat output by messing with the damper. This last year it was zero one morning outside, and nice and warm inside.

I've tried coal in the past but never was very satified. I could never get the danged thing hot enough. On the other hand, I can run you out of there if I'm using pine.

Pine burns for about 3 - 4 hours on a full stove, and will retain enough coals to fire start a fresh load of wood up for about another hour and a half. Not a problem since the call of nature usually gets me up anyway.

Plus there is a lot of standing dead trees available within a mile or two of camp. A single 1 hour run and I have enough wood for about 4 days.

Don't go with one of those cheap fold up stoves. You'll freeze.

Oh, and another side benefit. You don't need a gas stove to cook on. We cook everything on our wood stove. Eggs to steak.

AB