And now for something completely different. Here’s a homemade backpack stove powered by wax. It’s not just a big candle, which would be weak. This stove supercharges the hot wax vapor with air so it blasts almost like a regular stove.
The result is a strong, not terribly dirty, wind-tolerant flame. Compared to other stoves, it rates better or the same in many ways (and the same or worse in a few others).
As far as I know, nobody’s ever made anything quite like this before. You can make one, too: just click over to the Construction page.
Wax?! What's the deal with that?
When we think of burning wax, we think of a candle. Wax consists of long-chain molecules that are powerful but don't vaporize easily. A candle uses a wick to convert molten wax to a vapor that then will burn in air. Some of the heat from the flame converts solid wax to molten wax. The liquid wax then travels up the wick, the liquid turns to vapor, and the vapor flames, continuing the cycle. Many other stoves use a similar heat feedback cycle, except that only liquid gets heated to vapor, and no solid phase plays a role. Most canister stoves (propane, butane, etc.) employ no heat feedback, working only in the vapor phase, and so they perform poorly in cool weather.
A candle, obviously, puts out little power, and its little yellow flame is vulnerable to wind. Blow on it, and it goes out. Sometimes it's smoky. Just making a candle big, say giving it a huge wick (which this wax stove has, by the way), does little to solve these problems.
In contrast, fuels made of the smallest molecules, like propane and butane, vaporize readily, at room temperature. They spray out of a stove in vapor mode without any coaxing, and then they easily, vigorously mix with air to create a hot, efficient flame. Kerosene and Coleman® fuel can also be made to automatically mix with air in a stove burner head once the stove is pumped or primed. By the way, the older nonpumped, purely primed stove designs work well too and are much beloved by many. The last couple decades have seen a great variety of simple alcohol stoves emerge. Many of these also develop a bit of pressure and heat feedback and jet out their burning vaporized fuel for a dynamic mixing with oxygen.
In summary, then, this stove achieves a vigorous mixing of oxygen and vaporized fuel by injecting a forced stream of air and providing heat feedback to the solid/liquid wax.
How wax rates as a fuel
Wax is a fuel that contains about 18,000 to 19,000 Btus of chemical energy per pound. That’s essentially the same as the energy density of kerosene, Coleman® fuel, butane, propane, and similar petroleum-derived fuels. That’s because all these fuels, including wax, belong to a group of chemicals called alkanes. The main differences among the various alkanes involves the sizes of their molecules. For example, propane has 3 carbon atoms per molecule, whereas wax molecules have some 20 to 40 carbons. Propane consists of small, easily-evaporated molecules (three carbons), and thus propane needs to be stored in a strong container. If a propane canister were punctured, the fuel would boil away quickly, perhaps explosively. Wax, being on the high end of the range in terms of molecular size, doesn’t need a container because it melts and vaporizes only when heated to relatively high temperatures. Wax is quite safe and easily handled.
How about alcohol? Alcohol contains only about 12,000 Btus of energy per pound. Thus, alcohol contains only ⅔ the heating power of petroleum-derived fuels. For that reason, using alcohol in a stove leads to inordinately long waits for water to boil and a need to carry greater weights and amounts of fuel. Although alcohol needs to be stored in some type of container, its container doesn’t need to be nearly as strong as a container for propane or butane.
What else is going on in this stove?
Air enters the stove body through a round port on the side. The air then swirls around the entire fuel chamber, thereby heating the air, and enters the fuel chamber through the many air holes at the top. The heated air supercharges the flame and forms a swirling vortex that is mixed further by being ejected upward through a screen-like diffuser plate.
The supercharger sits beside the primary stove unit. This side-by-side layout makes the stove far lower and more stable than some other undermount-supercharger layout. The supercharger keeps all electrical components protected inside a self-contained unit. Its shell will shed cooking spills and a light rain.
The windscreen obviously protects the flame from wind, and the air tubing provides distance between the flame (often huge) and the supercharger.
The stove is cheap (but not easy) to make, is way more powerful than alcohol stoves and almost as powerful as traditional expensive commercial stoves, is heavier than many commercial stoves but not all, performs well in inclement weather (but then white-gas stoves do too), and performs somewhere in the middle of the pack in many other ways. Use of wax fuel gives it a special distinction. Here, below, is my attempt to explain the wax stove’s advantages and then, farther down, its disadvantages and areas where it’s "a wash”.
Inexpensive to make. Like all do-it-yourself stove projects, this stove can (pun purposely inserted) be cheap to make. That is, assuming you already have lying around some special tools and materials. See Construction page. The electrical parts will only set you back about $11.
Solid fuel. You’ll especially like this stove if you’re married to the idea that solid fuel is better. Wax fuel needs nothing besides maybe a wrapper in the way of containment: no bulky containers to carry around and dispose of. Wax is nontoxic, inert, nonvolatile, and nonexplosive (obviously). Indeed, wax is commonly added to foods and used in making candy. Molten wax, if spilled, will cool quickly, flow only a short distance, be easily extinguished, and never explode. If you use beeswax rather than paraffin, you’ll be using a renewable resource: declare your independence from foreign oil and greenhouse-gas petrochemicals. Beeswax has a high melting point of 143 °F, which could come in handy in hot weather.
Good performance in cold, windy weather. The stove does well in cold weather if adequately primed with an 80-20 kerosene-gasoline blend and allowed a few minutes to warm up. In contrast, canister stoves (using butane mixtures) perform poorly in cool temperatures, and most quit entirely somewhere between 0 and 32 ºF. The wax stove’s battery will function down to 0 ºF or lower, and anyway can easily be kept warm at around 95 ºF in a shirt pocket next to one’s body. The stove's output rates at about 6,000 Btu/hour. The stove’s flame is shielded from wind.
Difficult to make. Cutting, folding, and riveting the supercharger housing can be tricky. Hooking up the wiring requires (the barest of) electrical knowledge. Soldering the wiring requires special skill. Consider it a challenge. See the Construction page.
Moderately fast heating. The stove takes a few minutes to prime and get up to full power. That's largely because the wax first needs to undergo its phase change from solid to liquid. According to tests under standardized conditions, the stove then takes 8½ minutes to bring a quart of water to a boil. That boil time is roughly twice that of a typical commercial stove. That’s not bad, though, and it's good compared to boil times of 12 to 14 minutes using alcohol stoves. The wax stove has served me (us) well for parties of one to three on several treks.
Burn hazard. All stoves present an obvious burn hazard. However, in addition, the wax stove produces a pool of hot, molten, burning wax that will cause a nasty burn if spilled on the skin. If tipped over during use, the stove can leave a pool of burning fuel on the ground that would need to be extinguished by kicking soil onto it. After use, the molten wax will take several minutes to cool to a relatively safe temperature. Alcohol stoves, however, pose a similar hazard, and butane/propane and white gas are used under pressure, thereby posing (slight) spray, flareup, and explosion hazards if used improperly.
Moderate controllability. The stove has essentially two "settings": high and low, achieved by using and not using the supercharger, respectively. In the low setting, the flame is inefficient and may impart more soot on one's pot or pan.
Soot. The stove leaves one's cookware sooty. Some of the soot can be removed by pressing one's pot into soil and turning it back and forth.
Criteria where it's a wash
Functional practicality. The wax stove is about as compact, easy to use, and sturdy as most commercial stoves. Its fan is designed to run for thousands of hours, and its electrical components are probably about as robust (or delicate, your choice) as the plumbing, O rings, seals, pistons, springs, spindles, and other fragile parts in commercial stoves.
Weight. The stove's total weight as a system makes for somewhat complex comparisons. The stove itself, at about 13 ounces (with some fuel, a battery, and 1¼ oz. of priming fluid), is about in the middle of the pack of commercial backpack stoves in terms of weight. The battery will power the stove for 5 hours (conventional alkaline) or 12 hours (lithium), and thus an extra battery is probably not needed on most trips. Even so, an extra battery would weigh only 1 ounce (lithium) to 1½ ounces (conventional alkaline). However ...
Thirst. Typical conventional commercial stoves bring a quart of water to a boil using about 0.5 oz. of fuel. The wax stove performs this task using about 0.6 to 0.7 oz. of fuel. This greater thirst is due, again, to the solid-to-liquid phase change. This consequent weight disadvantage of wax is partly mitigated by the fact that wax needs essentially no container. You can pack wax fuel in just a paper or plastic wrapper rather than the metal canisters or tanks needed to pack conventional liquid fuel. So, even when factoring in the metal containers needed to hold petrochemical fuel, wax fuel weighs some 20% more. (Alcohol fuel including its containers, however, will weigh 50% more than wax to do the same heating job.) However, using wax fuel saves you from carrying bulky weighty empty fuel containers on the return-to-civilization leg of your wilderness journey. Thus, all things considered, thirst, or weight of fuel, is nearly a nonissue.
Cost of fuel. The stove’s fuel can be gathered from home candle drippings, trimmings, and leftovers and then molded into convenient fuel sticks (see Preparation). In that event, your fuel is essentially cost-free. If you buy wax at say $5 per pound from the local hardware store, then running the wax stove costs about half as much as butane or propane or about 4 times as much as Coleman® fuel. Wax, if bought, therefore rates somewhere in the middle in terms of cost. Already accounted for in these figures are (1) the rate of fuel consumption (see Thirst, above) and (2) the minor cost of the wax stove’s battery power at about 25¢ per hour.
Another new wax-powered stove, from elsewhere
Googling and browsing on YouTube around 2012 revealed this: A designer, Raymond Gatt, created a backpackable wax-powered stove that he called the G-Micro PSL.
Obviously, Gatt's design benefits from the use of inert, relatively safe, solid fuel — wax, of course — rather than liquid fuels with their various issues (toxicity, explosion potential, etc.). It's also far superior to our DIY project wax stove in many ways:
Elegant and well made
Extremely light: only 4 ounces
An efficient flame, with a relatively high blue-to-orange ratio
No electrical components and few moving parts
Still, I say “hurrah” for what appears to be a clever, lightweight, wax-powered stove appropriate for personal or small-party use. There was a website for this product with much interesting information and purchase ($99) details, but it had disappeared as of October 2014.
Execute this project and use any resulting product solely at your own risk.