by Will Rietveld | 2005-02-08 03:00:00-07
One of our favorite canister stoves: the Coleman Outlander F1 Ultralight, only 2.7 ounces and hot!
Canister stoves weigh as little as 2.5 ounces (71 g) and are very easy to use. Simply attach the canister to the stove, open the valve, light the burner, and cook. Canister fuels are designed to deliver lots of heat (BTUs/hr), with relatively good cold weather performance, in a lightweight container. A canister providing 8 ounces (227 g) of fuel weighs about 5 ounces (142 g) empty, not too bad for a steel container that must safely hold liquefied gases. N-butane, iso-butane, and propane - the principal fuels used - provide about 21,000 gross BTU/lb: about the same as white gas.
Fuel canisters come in different sizes (approximately 4, 8, and 16 ounces net weight). Different brands of blended fuel vary in the proportions of propane, n-butane, and iso-butane.
Why not use common propane instead? The problem with using pure propane is that it has a boiling point of -43 °F (-42 °C), which means that it has a high vapor pressure at common ambient temperatures, and therefore requires a heavy steel canister to safely contain it (like the heavy 1-pound propane canisters used for Coleman stoves and lanterns). So canisters of pure propane are too heavy for backpacking. Butane is easy to contain because it has a boiling point of 31 °F (-1 °C), but it doesn't vaporize well when the temperature drops below freezing. Thus, pure butane has major limitations for cool-weather backpacking.
The solution is to use a blended fuel consisting of propane, n-butane, and iso-butane. The thinner canisters can handle up to about 30% propane, with the remainder being n-butane and/or iso-butane (boiling point 12 °F/-11 °C). The propane/ iso-butane mix vaporizes well at lower temperatures and provides enough vapor pressure for adequate stove performance at colder temperatures. Basically the propane in blended fuels drives the system. With its low boiling point, it provides plenty of vapor pressure at normal ambient temperatures; the other gases are carried along and burned with the propane. There is evidence to indicate that the propane burns off first, causing performance to drop (lower gas pressure and heat output) for the last third of a canister. For an insightful discussion of stove fuels (and other stove topics), see Roger Caffin's article, Got Gas? Stove Theory and How They Work (click link to purchase PDF reprint), in Backpacking Light Magazine (print issue) volume 1, Summer 2004.
It is good practice to frequently inspect the canister connection O-ring on your stove (the black ring in the photo) visually for cracks and, once it is connected to a canister, to listen and sniff for gas leaks.
The EN417 canister specification and Lindal self-sealing valve are a standard adopted by manufacturers throughout the world. Because the Lindal valve is an industry standard, theoretically every brand of screw-threaded canister fuel must work on any brand of screw-threaded stove. There are legal registration requirements in each country to ensure compatibility with the standard. The basic problems are: 1) one manufacturer has no control over the quality control of another manufacturer's stove or fuel canisters, and 2) no manufacturer wants to accept any responsibility for another manufacturer's products. Especially with fuel canisters, which are a potential bomb in a worst-case scenario, company lawyers are averse to liability. So their position and message is that there are small differences (depth and height, manufacturing tolerances) in the threaded fittings on different brands of stoves and canisters. Consequently, to be on the safe side, every stove manufacturer strongly recommends using only their canisters on their stove. Some manufacturers go a step further with strong warnings such as: "Use of other gas cartridges can be dangerous." Obviously they want to avoid liability, but they also want to sell their own brand of fuel canisters. So what to do? Many backpackers have used different canisters on their stove for years without problems, and most of us do so when our brand is not available. A little experimentation quickly determines which canisters work on your stove and which ones do not. The usual indicator of canister incompatibility is no (or very low) gas pressure when you open the valve. This can sometimes be overcome by tightening the connection a little more (but be very careful not to overdo it!). The key safety factors are to check the O-ring seal in the base of the stove (see photo) to make sure it is in good condition, and check the connection for any leakage before lighting the stove. Put the stove/canister connection up to your ear and listen for a hissing sound, also put it to your nose and sniff for the typical ammonia smell from leaking gas. Never light a stove if there is fuel leakage from the canister connection.
Besides canisters with the familiar Lindal valve, European travelers will encounter Camping Gaz canisters that have a fitting that looks very similar to a Lindal valve, but is smooth rather than threaded. Compatible stoves use a clip to attach to the canister. If you want compatibility with both threaded Lindal valves and unthreaded Lindal valves, consider getting an MSR SuperFly stove. It has an attachment mechanism that works on both.
One pervasive myth about canister stoves is that the jet can clog from using other manufacturer's fuels. Snow Peak "fuels" this myth with their statement: "Fuel canisters manufactured by other companies may contain a mixture of fuel that has larger particles. These particles clog up the GigaPower stove and lantern." This is a pretty vague statement, and is pure hooey if they mean that larger fuel molecules will clog the jet. All canister stoves are jetted for C3 and C4 hydrocarbons to attain a desired BTU rating under a set of average conditions. The differences among stoves are not large enough to require a special fuel. The high pressure (up to75 psi) in the canisters keeps the jet clean. Clogs from the fuel itself are rare. What causes jet clogging is dirty connectors on the stove and fuel canisters. Keeping these connectors clean is good preventive maintenance to avoid stove failure in the backcountry and a trip back to the dealer. It is a good idea to retain the little plastic cap (if one is included with the canister) to keep the valve clean. I make it a habit to blow out the fittings of both the stove and canister before attaching the canister.
As I mentioned, cold temperatures reduce the vaporization of the fuel in the canister, and with less vapor pressure the stove burns sluggishly. If you use a blended fuel in cold weather, it is important to warm the canister before you use it so that the butane will vaporize and burn along with the propane and iso-butane. If you don't, the propane and iso-butane will boil off first, leaving you with a partial canister of butane that doesn't want to vaporize. The heat of vaporization (heat required to change the fuel from a liquid to a vapor state) of the fuel as it is burned also works against you, because the required heat for the phase change is drawn out of the remaining fuel in the canister, causing it to become even colder and less volatile. To counteract this, I suggest the following: 1) use full canisters (because they have more propane in them than a used canister), 2) warm canisters in a sleeping bag or inside your shirt or pocket, and 3) if you have a second canister, trade canisters when the fuel in the first one gets too cold.
Another tip is to choose the right canister fuel blend for cold weather. Fuel that is a mix of iso-butane (boiling point 12 °F) and propane, works better in below freezing temperatures than fuel containing butane (boiling point 31 °F), because the fuel in the canister will continue to vaporize (albeit more sluggishly) at cold temperatures. For cold temperature performance (below freezing), the propane is the basic driving force (because of its low boiling point) that makes the stove work; iso-butane will volatilize and burn along with the propane (but in decreasing amounts) down to its boiling point of 12 °F, while the n-butane will just sit there. Warming the canister will enable it to perform at even lower temperatures. Examples of cold weather fuels are: MSR IsoPro fuel - 80% iso-butane and 20% propane; Snow Peak GigaPower fuel - 85% iso-butane and 15% propane; and Jetboil JetPower fuel which is 20-30% propane with the remainder iso-butane.
When a canister of propane/iso-butane fuel is "empty" at below freezing temperatures, but you can shake it and hear fuel sloshing around inside, you have a partial canister of n-butane. Most iso-butane also contains some n-butane because it is difficult and expensive to produce pure iso-butane at the refinery.
Altitude offsets the effect of cold temperatures. The lower atmospheric pressure (with higher altitude) makes it easier for the liquid fuel to vaporize in the canister and supply the burner with gas.
As you ascend in elevation, atmospheric pressure decreases and water boils at a lower temperature. For every 18 °F drop in the boiling point of water, it doubles the time to cook food. For example, the boiling point of water drops from 212 °F at sea level to 194 °F at 10,000 feet. It takes twice as long to cook raw food at 10,000 feet than it does at sea level. So, if you are planning to cook raw food at higher elevations, be sure to bring extra fuel. For boiling water and rehydrating foods, altitude doesn't make much difference. It actually takes a little less time and fuel to boil water (since it boils at a lower temperature), but rehydration will take a little longer, which balances it out.
Most canister stoves are very sensitive to wind. We found that a 12 mph wind dramatically reduced the efficiency of all the canister stoves we tested, except the Jetboil, which was minimally affected. Basically, wind blows the flames away from the pot, so heat transfer is greatly reduced. In the worst case observed in our tests, a quart of water was warmed only 27 degrees Fahrenheit after running the stove at full throttle for 10 minutes! Some stoves performed much better; see our Lightweight Canister Stoves Test Report for details. Using a windscreen restored the performance of some stoves to near that of calm conditions. However, you should use a windscreen with extreme caution and knowledge of what you are doing (see section below). The MSR WindPro stove (not reviewed) is designed so that the canister and burner are separated, allowing the use of a tighter windscreen. There is a weight penalty for this feature, though.
An effective canister stove wind protection setup consists of a windbreak on three sides and a heat shield above the canister. The heat shield (center) is made from the bottom of an aluminum pie pan, and is fastened with a paper clip (right photo). If you choose to use a windscreen with a canister stove, it is imperative that you monitor the canister with your hand to make sure it does not overheat.
All canister stove manufacturers strongly recommend against using a windscreen because it can cause the fuel canister to overheat and explode, resulting in serious injury and/or death. Do not ignore this warning; there is significant risk if you don't know what you are doing. A windscreen could turn an accident into a disaster if a super heated empty pot or a boilover spilled more heat on an already overheated canister. The manufacturers' position is understandable considering the liability issues. However, they have done nothing to provide consumers with a safe and effective windscreen. Canister stoves lose a lot of efficiency when exposed to even a slight wind, so some type of wind protection is needed. Jetboil has developed the most effective integrated heat exchanger and windscreen of any manufacturer thus far, allowing it to maintain its fuel efficiency and boil times in windy conditions.
Many backpackers use some type of wind protection for their canister stove. They pile rocks, use a sleeping pad, or carry a conventional aluminum windscreen. It is safer to leave the windscreen open on the leeward side so it doesn't come too close to the pot and canister, and raise the windscreen above the ground an inch or two to avoid trapped heat (the heat deflected down from the bottom of the pot) so it does not overheat the canister. This windscreen setup doesn't warm the canister significantly. Think of it more as a windbreak than a windscreen. It's a compromise solution for blocking wind and reducing heat loss, but at least there is not much risk of overheating the canister. To be certain, feel the canister with your hand to be sure it stays cool. If it's too hot to touch, it's too hot!
Placing an aluminum heat shield (made from a pie pan, see photo) between the stove and canister protects the canister from heat that is deflected down from the bottom of the pot. In cold weather you may not need a heat shield, as long as you monitor the temperature of the canister with your hand. For an alternative canister stove windscreen design, see the Backpacking Light technique article, Homemade Canister Stove Windscreen, for construction details.
There are basically three factors that affect canister stove performance: burner design, heat transfer, and heat loss. Our tests show that there are significant differences in stove design that affect their performance; so choosing a top rated stove is the first step. However, the differences among stoves are small compared to the performance differences resulting from how the stove is used. To maximize heat transfer, use as wide a pot as is practical to maximize the surface area to absorb heat. Adjust your stove to minimize flame spillage around the pot, in other words - turn it down! Always use a lid on your pot to hold the steam in; letting the steam escape is a huge heat loss. Convection (wind) is by far the biggest heat robber, so providing wind protection is essential to obtain good stove performance. Use a windscreen properly with full knowledge of the risks and always be cautious. See our Lightweight Canister Stoves: Review Summary and Gear Guide Overview and Lightweight Canister Stoves Test Report for more information on individual stove performance.
"Frequently Asked Questions About Lightweight Canister Stoves and Fuels," by Will Rietveld. BackpackingLight.com (ISSN 1537-0364).
http://backpackinglight.com/cgi-bin/backpackinglight/canister_stove_faq.html, 2005-02-08 03:00:00-07.