The campfire reflector wall is somewhat the mark of the experienced outdoorsman. But do they actually work they way they are purported, to redirect heat at the back of the fire to someone on the opposite side of the fire all snug in their lean-to? The short answer is NO! It doesn’t, however, stop others from continuously preaching it and can be found in many survival books. In all honesty, I too, many years ago, believed it. But why doesn’t it work? Well, first lets look at what we are discussing, so we are all on the same page.
On the surface, it seems it would work, right? Science, however, tells us that it can’t and a simple experiment you can do at home will prove that it doesn’t. Inverse Square Law and more appropriately Inverse Cube Law says that it doesn’t work. But for the purpose of explanation we will use Inverse Square Law.
Inverse Square Law
Inverse-square law is any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity.
A clear example of this is dropping a pebble into a still pond. The concentric rings near the point of impact will be more intense and as the rings radiate outwards they spread out and lose intensity. This happens with light, heat, magnetism, gravity, etc.
You can do the same thing with a flashlight. Place the source of light near a wall and you will notice how intense it is. Now begin backing away from the wall and you will notice the light covers more area, but the intensity of the light falls off proportionately to it’s distance squared.
The same is true of heat. The closer you are to the campfire, the hotter it is. But as you back away, heat becomes less intense but covers a greater area at that new intensity.
Using the formula of Inverse Square Law, one will note that if we have a fire radiating at 100 degrees, when one moves back say two feet and square the distance one receives only a quarter or 25 degrees of the heat radiated by the fire
Look at the diagram below and position yourself at the position where the Yellow A is. Notice how the letter A has less red dots on it the further away from the source it is. That is Inverse Law.
So how then does this affect the reflector wall? Well, imagine the radiated heat on the other side of the fire also falls off at the same rate, which it does. Now in order to reach you, the already lost heat has to jump back over the source, losing more heat in the process, and reach you at what ever distance you’re at, losing even more heat. The fact is by the time it reaches back just to the heat source it originated from, it is not even measurable, because the temperature is below what the source is radiating.
I know, your head is spinning, right? Here’s the experiment I performed at home, to illustrate the effect.
I took an indoor/outdoor thermometer and placed the outdoor probe 6” away from the back stove, between the stove and the back wall. I turned on the stove and watched the thermometer climb until it became stable and the temperature wouldn’t climb anymore. In my case that was 103 degrees Fahrenheit. I then took the wooden cutting board I had and placed it 2” away from the heat source, a la reflector wall, on the opposite side of the flame, nearest me. Now keep in mind the cutting board was way larger in relation to the temperature probe than anyone builds a reflector wall in relationship to themselves or the fire. The results were, that even though the cutting board was only two inches away from the heat source, the temperature at the probe did not climb past 103 degrees, even after leaving the board in place for about 10 minutes.
Now, keep in mind, this was about as a controlled experiment as one could have. I had a constant room temperature in the kitchen of 74 degrees, without fluctuation, and I had a gas stove putting out a constant 103 degrees at 6” away. In the outdoors, things will not be so kind to you as any little breeze will diminish results exponentially.
So, the long and short of it is The Reflector Fire Wall does NOT work. But if you’re going to go through the effort of building one at least use it to as part of a system to draft smoke away, because using it to reflect heat back to your lean-to won’t work.