I am an airplane mechanic for a living and small twin engine aircraft are mostly heated using a combustion heater like this one http://www.kellyaerospace.com/articles/Heater_AMT.pdf , I figured there has to be a cheap way to make heat for tents and TD's that uses common hardware store items. Then as I was wandering around in the the blue Borg, (though orange is my favorite, we don't have green around where I live) I think I figured it out.
My idea is simple, a kerosene lantern, which is used by most of the people in the world, and two mailboxes. the rest is just using physics to get heat to go where we want it and soot to stay out of our lungs.
While searching for the BTU (heat output) rating of a kerosene lantern I found a site that reports that most people in the world without electricity use kerosene lanterns, and stoves, most of these are not vented to the outdoors, and this causes quite a few lung problems. SO WORK CAREFULLY, SEAL ALL YOUR SEAMS, AND IF IT IS WINDY OUT USE THE 12v FAN FOR POSITIVE PRESSURE SAFTEY.
One other note, while a candle is a better-than-nothing source of heat, it actually coats the inside of your tent, TD, and lungs with wax as it burns, and anything that burns is using up the oxygen in your tent or TD, every year people don't wake up in their tents due to using candles, lanterns, and stoves to heat. YOU ARE JUST VISITING THIS PLANET, DON'T CUT IT SHORT, PLAN AHEAD AND BE SAFE.
The figures I found show that a candle puts out 90-100 BTU's (per hour), a human being puts around 250 out (equal to a 100 watt incandescent bulb) and a kerosene lantern puts out 800-3000 BTU's (depending on model and wick width, if a mantel is used, etc.) I am using the cheap oil/kerosene lantern from wallyworld for this which I believe will give me 1000 BTU's input.
For comparison, my house has a rather small oil boiler rated at 85,000 BTU's, and a pellet boiler rated at 175,000 BTU's, Most homes have 100,000 to 300,000 BTU rated systems. However my TD is about 40 square feet compared to 1,200 sq ft in my house.
For disaster or emergency use a kerosene lantern is your best bet in most cases for light and now for heat, most wick type lanterns will run on olive, jojoba and just about any type of oil, kerosene or lamp oil may not be around when you need more.