The Xtreme Stove
Delivery and contents
The Coleman Xtreme Stove and the separately issued Trail Maintenance Kit were received in the original unopened display carton (for the stove), and the appropriate plastic Ziploc-type bag with stapled folded label (for the repair kit). Unfortunately, the small wrench in the repair kit had caused a tear to the plastic bag and several small items were found to be lacking, although an example of at least one of each of the spare parts originally contained within remained. The carton for the Xtreme stove contained the stove itself, the accompanying stuff sack, a “Green Key” for opening empty Powermax canisters for recycling, and the instruction brochure, this last a large folding printed sheet. The bag for the repair kit contained a similar folded sheet detailing repair operations. Although Coleman provided Powermax fuel for testing purposes, this would normally be purchased separately.
Website and Warranty
The Coleman website is large and complex (inevitably, given the range of products the firm produces), but with an excellent search feature that enabled me to quickly locate information on these items, which was relatively comprehensive.
The limited lifetime warranty provides protection (to the original owner only) against defects in workmanship or materials. Coleman will repair or replace any part (or the entire thing) if it is found to be defective, with a new or remanufactured stove or component. If the stove is no longer made at the time of claim, an equivalent product will be substituted. The original purchase receipt must be retained and provided, and the unit may be returned to an authorized service center (locations available by phone via a supplied 800 number) or to Coleman itself at a specified address. Normal wear and tear is exempted from the warranty, as are misuse, unauthorized service attempts and “Acts of God” including fire, flood, hurricanes and tornadoes. Also not covered are incidental damages, within the usual legal limits. In all, this is a perfectly standard product warranty, although I have rarely seen the old “Wrathful Deity” clause used in the context of camping gear.
Features and Design
The Coleman Powermax series of stoves have been on my “gear radar” for a few years, since they were first introduced. What has particularly intrigued me was the fact that these were liquid-feed canister stoves. Let me explain this a little. A standard gas canister contains fuel components (normally a mixture of one or more of the following: butane, isobutane, propane, isopropane) that are gaseous at atmospheric pressure. Under pressure in the canister, these gases are in their liquid phase, as a mixture of liquid components. When the stove is operated, the fuels revert back to their gaseous (vapor) phase as the stove control valve is opened (in effect, they boil when returned to atmospheric pressure). The emissions from the cartridge are mixed with air in the burner, resulting in a strong, hot flame.
Regular canisters are great for three-season stoves, and are light and efficient. Those stoves that sit directly on the canister are a little difficult to shield from wind without creating some potential for over-heating the canister, which can be dangerous. However, in winter, without special precautions, the canister contents may be at a temperature below the boiling point of some of the constituent gases. This results in poor performance.
In such near- or sub-freezing conditions, the most volatile component of the fuel (often propane, with the lowest boiling point) burns off first, leaving butane and iso-butane, which don't vaporize as readily in the cold. The stove, despite the fact that shaking the canister indicates an abundance of fuel, may not burn well, and (in fact) may fail to work at all. Adding to the complications is that certain basic physical laws of gases (the Venturi effect) dictate that canisters will cool further as the gaseous contents discharge. Even on a warm day, if a gas canister is vented quickly, it will feel cold to the touch or even become frosty.
There are ways to deal with these problems, up to a point. I've often carried a canister against my body before cooking in winter, or have slept with it in my sleeping bag. There are other techniques (some involving minor stove modifications, which may prove dangerous to the inexperienced), but the long and the short of it is that conventional canister stoves have some serious (though not insuperable) drawbacks in the winter months.
The most common winter solution is to use a stove that's designed to burn white gas (basically, gasoline) or a similar fuel. In such stoves, the fuel is poured into a tank, where it is pressurized with a pump. Then, when the valve is opened before igniting the stove, liquid is pushed through the fuel delivery system to a pre-heater, a coil of tubing that sits within the circumference of the burner. To work, the stove must first be pre-heated (primed) by burning a little fuel below the pre-heater coil; then, when the liquid fuel is allowed to enter the tube from the tank (driven by air pressure), it vaporizes, is mixed with air, and is ignited at the burner.
Such stoves are quite reliable, but they have a few drawbacks. They tend to be rather noisy in operation; they can be a bit of a fiddle to light with cold, numb hands (the priming is often a minor chore); they are famous for occasionally (usually as a result of operator error) erupting in jets of flame or veritable fireballs; and (in part, because of the pump) they are generally a bit heavy. In addition, fuels such as white gas are wonderful solvents for modern synthetic fabrics, so woe betide any camper who spills fuel in their pack.
The Coleman Powermax stoves appear to combine the best of both worlds, especially for winter use. The Powermax fuel canisters contain a 40% propane/60% butane blend. This is an unusually high percentage of propane, and by itself this guarantees that the canister would outperform most on the market, both for thermal output and operation in the cold. However, the key to this stove's functioning is not so much the fuel composition as the fact that it is a liquid feed stove. Indeed, so far as I am aware, it is the only gas canister stove with this feed mechanism on the US market.
The burner, as expected with a liquid feed stove of any type, has a pre-heating tube, but because of the low-temperature volatility of the propane fraction of the fuel, I would not anticipate (under the sort of winter conditions I encounter) having to prime the stove; it is, in effect, self-priming (in the event that I do need to do so, I will heat the coil with my Brunton Helios). Nor do I have to carry a pump, as the cartridge is pressurized sufficiently by the liquefied gases within. The cartridge is lightweight aluminum, and (again unlike every other cartridge I know) it is recyclable. When empty, it may be carefully pierced with the “Green Key” and left roadside for pickup with other reusable glass and metals, or otherwise recycled.
Powermax fuel is available in two canister sizes, 300 g (10.6 oz) and 170 g (6.0 oz). The weight quoted on the canister is the fuel weight. The larger canister weighs approximately 3 oz (85 g) over this, at about 13.5 oz (383 g), including the resealable plastic cap. I have been unable to locate the small canister locally, as of this writing, and so I am unable to provide the canister weight for the smaller version. Because the hexagonal valve mechanism used by Powermax fuel canisters is unique to Coleman, at least so far as fuel is concerned (these canisters do not use the same type of Lindal valve as most on the market), only Coleman's fuel can be used with the Xtreme stove.
Stove diagram
Valve and hose assembly
The canister attaches to the stove's valve assembly (see image above). This (as with much of the stove) is made from a lightweight magnesium alloy. The cartridge attaches to the fuel valve by pushing in and turning the canister until it locks, about one-eighth of a turn. The valve of the canister is at that point seated against a small O-ring seal, assuring a tight connection. This seal, as well as the components that hold it in position, are part of the Maintenance Kit, so that if any portion of this crucial connection is damaged, it can be repaired. A fine-nosed pair of pliers (of the kind usually found on, for example, a Leatherman multi-tool) is required for this job. A small Phillips screwdriver (again, an item found on most multi-tools) is also required, as is a pocket knife blade. The only other tool necessary for field stove repair is the open-end wrench, which is included with the Maintenance Kit. I will be examining ease of repair during the test phase of this report.
It's interesting to note that the valve assembly is finned. Rather than being designed this way for cooling purposes, my guess is that this is to maximize the area of the valve unit exposed to the air, so that warmth absorbed will help offset any cooling as the fuel flows in. I anticipate that this cooling should be much less extreme than with a standard canister stove; again, I will be examining this aspect of the stove's performance. There's a wire foot attached to the valve assembly, which helps keep the canister and valve upright, so that the flow control valve knob is always accessible. Below the sides of the plastic knob (which is ergonomically designed for ease of operation), the valve assembly has the on and off direction very clearly marked. A label affixed to the wire foot provides lighting instructions and precautions in French and English (oddly enough, not in Spanish, though that language is represented on the main instruction sheet).
Leading from the valve is a wire hose that conveys the liquid fuel to the burner assembly.
Burner assembly
The fuel from the hose enters the burner at the base, via a screw-threaded brass tube extending from the wire hose. From there, it is conducted to the generator where it is vaporized in the preheat coil. It then passes through a wire screen (to remove solid impurities) and a gas tip, before entering the burner assembly proper. The repair kit contains spare screens and two gas tips, should any problem arise at this critical juncture in the system.
The generator and other components at the base of the lamp are made of brass. Once in the burner tube, the gas mixes with air and passes up to the burner, where it passes through a metal mesh and then one of the many holes and ignites, producing a complex pattern of jets. I will be examining how well the flame pattern works with pots of various sizes. The burner itself is surrounded by the burner bowl, which is supposed to act as an integral windshield, according to the packaging. I'll want to see how effective this arrangement is in a breeze, and whether it needs supplementing with a windshield proper (since the canister and valve are separated from the body of the burner by the hose, a foil-type windshield is perfectly safe to use).
Based on some initial testing (home, not field), the heat output of the stove at the full setting is prodigious. I whipped up a batch of squash and carrot soup (eventually topped with toasted green pumpkin seeds) in a full-size pressure cooker. Though I did not time it, the pressure cooker started venting extremely quickly, as fast (or faster) than my kitchen range. I was impressed. I can't wait to see how it handles a wok! It's unlikely, to say the least, that I'll take either of these utensils on the trail, but they serve to provide an indication of the thermal output of the Xtreme stove.
Leg and grate assembly
The burner is held upright by three legs, to which are attached the grate (or pot-rest). When in storage, these legs fold together. Each has a rubberized foot. The legs are made from the same magnesium alloy as the valve, and they are held in position by the tension of the spring. The legs move fairly freely and, unlike some other stoves I have used, do not truly lock into place. As a consequence, I will be carefully monitoring the stability of the leg assembly. The pot rests, made from steel, are attached to the legs via a fitting. The upper surface is notched to avoid slippage (as can be seen in the photograph) and is curved. According to the box, the curvature is designed to enable pots to sit level if the burner is on an uneven surface.
Operation
According to the manual (and verified in practice) to operate the stove, the canister is connected and the legs of the stove are deployed. A lighted match (or a lighter) is held to the burner, and the control knob is turned an eighth to a quarter turn. It's recommended that the stove not be turned to full for thirty seconds. This may be to ensure that the preheat coil is fully operational. To turn the stove off, the knob is turned in the reverse direction, and the fuel cartridge is removed. Naturally, the body of the stove will take a few minutes to cool.
Instructions and Precautions
The instructions provided by Coleman for use with the stove and the maintenance kit are extremely detailed, and easy to follow, and are presented in English, French and Spanish. They include an exploded diagram of stove parts, together with a parts list, useful for ordering replacement or spare components. There is a diagram demonstrating the use of the Green Key in cartridge disposal, the warranty (as already discussed), and a list of ”Things you should know.” The operating instructions (most of which have been discussed in the previous section) have detailed photographic illustrations and are very easy to follow.
An especially important section of the sheet details operating precautions. Some of these are obvious, or so I would hope, e.g. keep out of reach of children, do not use if there is a smell of gas, etc. It is recommended that the stove not be used in unventilated or enclosed areas (such as tents), as it depletes oxygen (and, as noted on the cylinder, carbon monoxide is produced as a by-product of the combustion of the fuel). It's also strongly suggested that the seal (the O-ring) be inspected before each use.
Proposed testing Strategy
Testing environment
I backpack, on average, at least once a month (trips of one to three nights), in the Catskill or Adirondack Mountains of New York State, camping in winter to elevations of approximately 4000 ft (1220 m), lower (as dictated by park regulations) in other seasons. In October, the weather will start to cool (in fact it already has), and although we may still have some fairly warm days, nights will be chill. I believe we have already had our first nights below freezing at elevation. By the end of the test period, in January, nights will be consistently well below freezing, and likely enough, bitterly cold (down to -20 F, -29 C) at elevation. I intend to test the stove according to the details below under these various conditions.
Testing details
In addition to testing details specifically discussed in the text, the following is the testing outline I will follow.
1. Efficiency: How efficient is the stove at low temperatures? Does it light easily (both in warm and cold)? Does the flame burn cleanly, without flare-ups? Does the strength of the flame vary over the life of the cartridge? Does the flame pattern lead to any serious hot-spots? Is this an effective stove for snow-melting? How controllable is the flame; will it turn down low for simmering (a failing with many otherwise excellent stoves)? How long will a cartridge last with this stove under varying conditions?
2. Utility: Does the stove assemble swiftly and easily, with easy movement of the legs? Is assembly also straightforward with gloved hands? Can I be certain that I have a tight seal to the canister? Is the stove stable on its tripod legs under different loads, and the pot secure on its supports, (a couple of liters of snow melt can put quite a strain on a stove)? Do I need to warm the cartridge for optimum performance at low temperatures, and if so, what's the best way of doing so?
3. Durability: Will I need to use the repair kit in earnest? How easily may field repairs be conducted? Can repairs be done in gloved hands? Will it stand up to the usual abuse of camping? Will spilt liquid (boiling over, etc.) cause corrosion problems?
4. Packing: Does the stove fold down to a small, neat size? How much room do the Powermax cartridges occupy, and do they need any special protection? How easily and safely are the empty cartridges recycled?
As this test is also of the Stove Maintenance Kit, I will be keeping a close eye on performance and will replace any parts (gas tips, o-rings, probe seals, screens, cams, fingerplates) that seem to need maintenance. Indeed, I will replace most just for the heck of it, to see how well the stove can be field-repaired.
I very much hope to test all of these issues, and any other concerns that occur to me over the duration of the test.
I thank BackpackGearTest and Coleman for permitting me to participate in this interesting test.
