Suppose all you are going to have is temprary shelter in the wild as you self-rescue or travel out of a disaster area. Maybe an improvised or small tent from your BOB supplies; maybe enhaced by getting up under a large bushy tree or in sheltering rocks.

You have to move and you need to get warm to recoup energy for moving, sleep, etcetera. Fuel for wood fire is available, but not much. Rocks may not be readily available. You have one water carrier container. You do not have much time each day to deploy your heating strategy.

What is the best and least elaborate way get adequate heat into your sleeping area for a whole night? What is the best and least elaborate combination of strategies to accomplish the goal?

dig a hole in your shelter where your bed is going to be, heap hot coals in the hole and cover with dirt. Make your bed on top, that's the best I can come up with, within the described parameters.

My thoughts also went to buried coals. It's a technique I've never tried and if it's something you want to use, try it in benign conditions so you know how deep, how much dirt on top -- too much dirt and you lose the heat, too little and you get hot spots. Ron Hood covers the Firebed in his Woodsmaster© Volume 2 Shelter.

It would be hard to find many areas that don't contain trash. Try to find a can and punch some holes around the bottom (bottom of the vertical walls, not the bottom bottom) with your knife. Get a fire started with debris in the bottom, and gradually add twigs, fir cones, dried grass (twisted and knotted), etc. Set this little stove on a flat rock if possible (it will retain some heat), or on bare ground.

"You do not have much time each day to deploy your heating strategy."

If heat is important to your survival, you'd better MAKE the time. And don't wait until dark.

Sue

In my experience, an hour spent on insulation brings twice the benefit of an hour spent on fire. Aside from boiling water, and some undeniable psychological cheer, a fire is there to dry out your person and your insulation (clothing, bedding). A bed of boughs (or dry grass or moss) to keep you off the ground is top priority, absolutely essential.

My 0.02

two long,low fires and sleep between them,or just one big whopping blaze and hope for the best...

Arranging a heat reflector behind a small fire can greatly increase the felt heat output by sending the warmth toward you instead of allowing it to be scattered. Logs, a board, rocks can be used close to the fire. You can further focus warmth by placing a reflector behind yourself. A tarp will work and it can pull double duty by acting as a windbreak, making you feel warmer by reducing heat loss. Mylar space blankets work really well as reflectors.

Also a small fire placed closer and using reflectors is more effective, and fuel efficient, than a large fire.

If your thinking of something less logistically involved one of the most efficient methods of warming someone I know of is to have them crouch or sit and place a large garbage bag with a head hole cut into it over them and placing a heat source, candle, candle lantern, oil or carbide lamp, under the edge of the bag. The heat rises into the bag where it collects and warms the person. You have to be careful not to set the bag, ground cloth, or any clothes present, on fire but it works very well.

By varying the flame height of the heat source, the amount of air you let in under the bottom of the bag, extending you legs out of the bag, and using your head to open or close the head hole it is possible to regulate the interior temperature. If the heat source is one that is one you can reliably regulate to a low setting and burns a long time it is possible to nap in such an arrangement.

In cold conditions it help to place some insulation, assuming you have anything dry, between your back and the bag. Also don't make the head hole too large. A good quality garbage bag will stretch around you head a bit without tearing. This technique, like so many other things, works best if you have tried it a few times before getting it to work in a critical situation.

Pay attention to where you locate your shelter. A difference of just a few feet can make a difference in exposure to wind, which is likely to be your biggest problem. Brush and thickets will shield you from breezes, while that inviting clearing may be rather drafty.

Avoid the bottom of drainages if you are concerned about the cold. Temps are often 5 to 10 degrees warmer only a few feet upslope.

Evaluate the possibility of traveling during a portion of the night. Exercise keeps you warm. This is dependent upon the terrain, your familiarity with it, the light sources you have with you, and moonrise.

If your fuel is limited, consider not building your fire until later in the evening or early morning. In my experience, 3 AM is the toughest time for an impromptu overnight.

Eat well and carefully. Ingest fats for long term metabolism. Bundle up early and stay out of the wind. Get insulation on your head and neck

Keep your spirits up, maintain a positive attitude, and look forward to a nice cup of tea to get things started in the morning.

Consider filling secure containers as "hot water bottles."

Arrange whatever you need to avoid having to exit the shelter and let in cold air that must be heated again.

If you have companions, get friendly in a share-the-body-heat sort of way.

Keep the space you have to heat as small as you can.

Consider found insulation like leaf litter, dry grass, appropriate evergreen branches, especially between you and the ground.

Save the firewood for later. Don't use untill you get very cold. Assuming that you can build a shelter of sorts or have a tent then this is your best bet.
http://www.heinnie.com/product.asp?s=wvpiv9703038&strParents=&CAT_ID=0&P_ID=4581

I have used these and its remarkable how much differance a candle can make.

Usual words of caution about ventilation.