Tuesday, November 29, 2011

Cold Weather Tips for Gas Stoves

OK, short and sweet, here are some practical tips for using (canister) gas in cold weather:
Peaks and snow, Sierra Nevada Mountains
First, choose good fuelAvoid "regular" butane and only use isobutane/propane blends.

Second, start with a warm canister. Keep the canister in your bag/quilt at night or in your inside jacket pocket (or something) during the day.

Third, keep the canister warm by placing the canister in water. If you chose good fuel in the first step, your fuel vaporizes at least at 11F/-12C. Liquid water will always be above 32F/0C -- that's about 20F/10C degrees above the vaporization point of the fuel. As long as that water stays liquid, you should have good canister pressure, even if the air temperature drops below the vaporization point of your fuel. It's the fuel temperature that matters, not the air temperature.  There are other ways to keep a canister warm which you can read about elsewhere, but water is safe and effective and is my preferred method.  WARNING:  Do not use hot water Tepid or even warm is fine, but hot water may cause your stove to flare.

Fourth, heat the canister if needed.  How can you tell if the canister needs more heat?  Poor performance.  If your stove's flame is insipid  in cold weather, try taking a spoonful or two at a time of hot water out of the pot and putting it into the water that the canister is sitting in.   Your performance should improve as the water gets hotter.  If performance does not improve even though the water the canister is sitting in is warm to the touch, there may be something else at issue such as low fuel level or a partial blockage in the jet.

Note:  If you want a detailed explanation of why this is so and what's going on behind the scenes, please refer to Gas Stoves: How Cold Can I Go?

That's it.  Choose good fuel, start with a warm canister, keep the canister warm,  and heat the canister if needed.  Happy cooking.  :)


Related articles and posts:

Monday, November 28, 2011

Gas Stoves: How Cold Can I Go?

Gas stoves (also called canister gas stoves) can struggle in cold weather.
Frozen lake and snow, Sierra Nevada Mountains
UPDATE, 17 December 2014:  I've almost completely re-written this article.  I've tried to talk more about the overall process of planning for cold weather trips.  I've also tried to talk about more than just the gas in a canister; I've added discussion of the practicalities of cold weather canister operation.  One should not rely on the gas alone but also on one's own planning and techniques.

So, how cold can I go with my gas stove?

Good question.  Do you want the short answer or the long answer?

The "Short" Answer
The short answer is that for the typical upright canister stove (that's the kind where the burner screws directly onto the canister), about 20°F/-7°C can be used as a rough planning number.  For a longer answer, see the appendix.  Understand though that the colder it gets, the more your stove will struggle even if it's warmer than my planning number.  Your stove will not work just as well at 20°F/-7°C as it will at 75°F/24°C, at least not without planning and intervention on your part. You will need to know the basics of cold weather gas stove operation which are:
  • Choose good fuel.  See What's the Best Gas for Cold Weather?
  • Start with a warm canister.  Keep the canister in your sleeping bag with you before breakfast, put the canister under your clothing before supper, etc.
  • Keep the canister warm. Put some insulation under the canister (closed cell foam works well), protect the stove from wind, and put the canister in a bowl of (liquid!) water.
  • Heat the canister if needed. How can you tell if you need to heat the canister?  Poor performance.  If your flame is insipid in cold weather, you need to (carefully! slowly!) heat the canister.  See my Stoves For Cold Weather article in Seattle Backpackers Magazine for some ideas on how to heat the canister.  
Now, I've described 20°F/-7°C as a rough planning number.  What do I mean by that?  Well, if you follow the basics of cold weather gas stove operation (select good gas, start with a warm canister, keep the canister warm, and heat the canister if needed) and use your head, it shouldn't be too difficult to keep an upright gas stove going in temperatures at or above the planning number.  If you look at a weather forecast for the area and elevation in which you intend to use your stove, you should be able to get some idea of what temperatures you can expect.  If the temperatures are well above 20°F/-7°C, you might plan to bring an upright canister stove. If the temperatures are forecast to be close to or below 20°F/-7°C, you might plan on bringing something else.  For some alternatives, read the Alternatives for Colder Weather section of this article.

Note that 20°F/-7°C isn't carved in stone anywhere.  This is just my fairly conservative rough planning number.  Particularly with a fresh canister, you might be able to go colder.  You may also get some cold weather performance increases at higher elevations where the boiling point of the fuel is lower.  More on that in the appendix if you're interested.  Note that this "planning number" is but one part of the overall planning process.  There are many factors that should be considered when choosing gear for a particular trip, and this planning number is just one of them.  My "planning number" is meant to be incorporated into one's overall planning process.  It is not intended to trump the planning process.

I've said that the canister needs to be heated in cold weather in order to get good performance from a canister gas stove, but NEVER OVERHEAT A CANISTER.  If the canister feels so hot to your bare hand that it's painful, that's too hot.  Take IMMEDIATE action to reduce the heating of the canister.  Overheating a canister can do a number of bad things including causing the canister to explode.
Crags and peaks, Sierra Nevada Mountains

Alternatives for Colder Weather
If you need to go colder than 20°F/-7°C, you have a couple of options.  One is to switch from a canister gas stove to a liquid fueled stove, that is a stove fueled by white gasoline or kerosene (or similar).   That's certainly a pretty tried and true approach.

But many people either don't feel comfortable with or don't want to hassle with liquid fueled stoves.  In particular, many people are intimidated by having to prime a liquid fueled stove.  Are there any options for canister gas in temperatures lower than my rough planning number of 20°F/-7°C?  Well, if you want to use canister gas, you might want to bring a stove that can handle liquid feed gas, a remote canister stove with the canister inverted in other words.  See my article, Stoves for Cold Weather II, for more information on liquid feed gas.  With liquid feed gas stoves, one can use gas in colder temperatures, something on the order of 20 Fahrenheit/11 Celsius degrees colder than upright canister stoves – if you use your head and follow the basics of cold weather gas stove operation.  My rough planning number for upright canister stoves is 20°F/-7°C and inverted canisters stoves have roughly a 20 Fahrenheit/11 Celsius degree advantage over upright stoves, therefore I use 0°F/-18°C as the rough planning number for inverted canister stoves.

Note that even with liquid feed gas, one still needs to have some pressure in the canister to drive the process.  Therefore you must keep the canister "warm" relative to the outside environment.  Placing the canister in water is a safe way to keep the canister warm.  Water freezes at 32°F/0°C, so, as long as the water is liquid, your canister will be warmer than 32°F/0°C.  Keeping the canister above 32°F/0°C should give you more than enough canister pressure to run your stove.

The planning numbers I suggest are guidelines for reducing risk; there are no guarantees in the back country.  The planning numbers I suggest are temperatures in which you should be able to keep your fuel sufficiently warm to operate a canister gas stove.  Keeping the canister warm requires intervention on your part.  Note however that "stuff happens."  If temperatures drop, if winds pick up, or if you are exhausted or injured, you may not be able to keep your fuel warm.  You must be prepared to handle these and any other unexpected changes or emergencies that may occur.  These planning numbers cannot be used alone.  You must engage in proper planning, bring the proper equipment, and you must know and use the basics of cold weather canister operation.

Finally, the colder you go, the harder it is to keep the gas warm in a canister.  If you're going out in really cold weather, ask yourself:  "Can I really keep the canister warm?"  In cold weather, an abundance of caution is the best advice I can give you.


Appendix – The "Long" Answer
So, what am I basing my planning numbers on?  Well, let's talk a little bit, at a high level, about the chemistry of canister gas.  If this gets too boring or confusing or if you disagree or you just plain don't like what I've written, I commend to you a much simpler approach in Cold Weather Tips for Gas Stoves.

Now for the "long" answer:  Canisters for backpacking typically contain propane mixed with either isobutane or "plain" butane (n-butane).  The boiling points (vaporization points) at sea level of each of these gases are as follows:
 Boiling Point
n-butane    -0.5°C    31°F
isobutane    -12°C    11°F
propane      -42°C   -44°F

When you blend the fuels together, your boiling point will be somewhere in between the boiling point of the various fuels.  Calculating the exact boiling point is not trivial.  Not only that, but the proportions of the fuel mix will change over time with an upright canister stove.  Why will the mix change over time?  If the canister is used in the normal, upright position, the propane will boil off at a faster rate than either n-butane or isobutane because if its higher vapor pressure.  Since the propane is boiling off faster, there will be less and less propane in the mix over time.  As the percentage that is propane declines, the boiling point rises.

OK, so why all this blather about boiling points?  Well, the boiling point is the temperature at which your fuel will turn to vapor, i.e. change from liquid to gas.  Canister gas stoves require gas to operate, but that's a liquid inside your canister.  Just shake the canister if you don't believe me.  That's a liquid in there.  The fuel inside the canister is under such high pressure that the gas liquefies (turns into a liquid).  In order to run a canister gas stove, that fuel has to vaporize.  In order to vaporize, the fuel must boil.  If the fuel temperature is lower than the boiling point, it won't vaporize, and your stove won't run.  For canister gas stoves in cold weather, we want the lowest boiling point possible so that the fuel will turn to gas so that we can run our stove.  We must then keep our canister warmer than the boiling point of the fuel.

Well, OK, if the propane is burning off and the boiling point is constantly changing, how the heck can I figure out how warm I have to keep the canister!?  Well, toward the end of a canister, all of your propane will have burned off, and you will just have the fuel with the highest boiling point remaining (either isobutane or n-butane).  Therefore the boiling point of your fuel will never be higher than the boiling point of the fuel that remains at the end of a canister.  All we have to do now is keep the fuel temperature is above the boiling point of the worst cold weather performing fuel.  Isobutane boils at 11°F/-12°C; n-butane boils at 31°F/-0.5°C.  Isobutane therefore is a much better fuel in cold weather.  This is why I stress that one should avoid n-butane and only purchase fuels containing isobutane and propane for cold weather use.

I've just described in the preceding paragraph how the propane burns off more quickly when the canister is used in upright mode.  If you read the "Alternatives for Colder Weather" section, I talk about using a stove that can handle the canister in inverted (upside down) mode.  One of the advantages of using a canister in inverted mode is that your fuel mixture doesn't change much over time.  Since you're pulling liquid off the bottom instead of gas off the top, it doesn't matter which fuel boils at what rate so long as there's enough boiling to produce sufficient canister pressure.  Since you're not losing your propane (your best cold weather fuel), your boiling point stays low.  Remember, you want the lowest boiling point fuel for cold weather.

Now there's another matter:  Canister pressure.  Just being above the boiling point isn't necessarily enough.  If our fuel boils at 31°F/-0.5°C, and the fuel temperature is 32°F/0°C, then it's not going to boil very vigorously, and we're really not going to have enough pressure to run a stove properly.  To illustrate this, think of the "chattering" lid on a pot of boiling water.  If the water is just barely boiling, the lid is quiet.  But if you turn up the heat, the water will start boiling vigorously, producing enough steam to literally lift the lid for a moment.  The lifting (as the pressure builds up) and falling (after the pressure is released) is what causes the noise of a "chattering" lid on a pot of boiling water.  In order to run a stove, you want the fuel temperature to be high enough to produce a vigorous boil.  How high above the boiling point does the fuel temperature have to be to have enough pressure to properly run a stove?  Well, I suppose it depends on your definition of "properly" (as well as some external factors like atmospheric pressure and temperature), but the bottom line is that if you turn on the stove and the flame isn't strong enough to cook with, then the fuel is most likely too cold and you may have to warm the canister.  If you want numbers, if the fuel temperature is 20°F/7°C degrees above the boiling point of the worst performing fuel, then generally you should have good canister pressure.  The performance of your stove, however, is the bottom line as to whether or not your fuel is warm enough.  Caution:  If you heat the canister, and performance doesn't improve, think.  Could there be some other problem, for example, a blockage in the jet or an empty canister?  If you keep adding heat and performance doesn't improve, there's something else going on.  Never heat the canister to the degree that the canister feels painfully hot.

And there's yet another issue:  Canisters get colder as you operate the stove, through the process of evaporative cooling.  Canisters cool from within and get colder than their surroundings.  Take a look at the below photo.
Ice forming on the lower portion of a canister in cold but not freezing weather
That's ice forming on the sides of the canister even though the temperature is not below freezing.  Why?  Because as I use the gas, evaporative cooling occurs, and the canister gets colder than its surroundings.  So starting with a canister that is warm enough in the beginning is no guarantee that the canister will stay warm enough throughout the time that you are cooking.  This is why I suggest heating the canister if needed.  Heating the canister counteracts the effects of internal canister cooling as well as cooling due to heat lost to the environment.  Here's another advantage to using stoves with the canister inverted:  the canister doesn't cool from within to the same degree as a canister does when you use it upright.  Thus, there are two advantages to using the canister upside down (if your stove will support it!):
1.  Your propane won't be leaving the mix.
2.  Your canister won't get as cold.
More propane + warmer canister = better pressure.  Inverted canister stoves are definitely superior for cold weather.

Now, another complication, but this one generally works in our favor:  As you ascend, the higher you go, the lower the atmospheric pressure.  As the atmospheric pressure drops, so does the boiling point of your fuel.  Generally, the drop is about 1.0 degree Fahrenheit for every thousand feet in elevation gained.  In metric units, that's about 0.5 degrees Celsius colder for every 300 meters in elevation gained.  Note the use of the word "about."  The actual values are higher, but I'm going to be conservative here.  I'll say more about why in a moment.  Take a look at the below chart.
A chart showing:
The relationship between boiling point and elevation for isobutane, navy blue line, 
Temperature vs. elevation for an internal canister pressure of 5 psi gauge (psig) for isobutane, red line.
Temperature vs. elevation for an internal canister pressure of 10 psi gauge (psig) for isobutane, gold line.
The relationship between the freezing point of water and elevation, green line.
Values are illustrative not exact.
The navy blue line shows how the boiling point gets lower as elevation increases.  Now, of course it's atmospheric pressure that's the real issue, but since atmospheric pressure declines relative to elevation at a fairly steady rate over the interval shown here, I show elevation.  In reality atmospheric pressure varies not only with elevation but also with conditions, and the change relative to elevation is not really linear (but it's close).  The chart is a simplification of what's really going on.  But recall that we're just after a rough planning number, a planning number that will be incorporated into our overall trip planning process, not a number that will override all else, so this chart is sufficient for our purposes.

OK, now why do I only use 1 degree Fahrenheit per 1000 feet in elevation gain (about 0.5 C per 300m) even though the actual change in boiling point is (slightly) greater?  Well, let's look at the red and gold lines on the above chart.  The red and gold lines illustrate what we're really after:  Canister pressure. Notice that the red and gold lines are not parallel to the navy blue line.  As it happens, the pressure inside a canister is lower in cold even if we're the same number of degrees above the boiling point.   In colder temperatures, the fuel temperature must be higher above the boiling point to produce the same internal canister pressure.  Notice how the red lines and gold lines get progressively farther away from the navy blue line.  The red and gold lines represent a constant pressure (5 psig and 10 psig, respectively).  In order to maintain a constant pressure, the red and gold lines have to get progressively farther away from the navy blue line as temperatures get colder.   Note that these lines are not exact; in fact I've exaggerated them slightly for illustrative purposes. Also, the actual functions are not linear in progression (but they're close).  We're not planning a Mars mission here.  We just need a rough planning number.  Approximating the true, non-linear progression with a linear one will get us in the ballpark.
An MSR Reactor operating at over 23,000 feet/7000 meters elevation on Muztagh Ata (24636'/7509m) in far western China. Overnight lows approached -40°F (which is also -40°C; the scales are equal at -40°). One person died on the mountain during this expedition.  It was cold.  Note that the canister is labeled "Isobutane" on the side.
Photo credit: Reuben Brimfield
Another note:  You can't out climb low canister pressure.  Some people have jumped to the conclusion that I'm saying "just keep climbing to the elevation where the boiling point is so low that your stove will start working."  Uh, no.  Temperatures fall faster than boiling points.  In other words, as you climb, it's going to get colder faster than the elevation change will improve your stove's performance.  The proper thing to do is to get a good understanding of the temperatures you'll be facing on a given outing and be prepared for them.  Don't try to climb to improve your stove's performance.

Now, look at the green line.  This represents the freezing point of water.  Note that the line is flat.  The freezing point of water does not vary with elevation the way that the boiling point of our fuel does.  Any liquid water will generally be warmer than the temperature that the green line represents.  Yes, the presence of certain minerals can change the freezing point of water, but for the purposes of our rough planning number, we will assume that any water that is liquid will be warmer than the green line.  Note that the green line is almost always above the gold line.  In other words, if we put a canister in water, you should have good canister pressure, so long as the water remains liquid.  I'm assuming here that you followed the other basics of cold weather canister operation as well.  This is the beauty of using water as a method of heating the canister.  By the mere fact that the water is liquid, we generally will have enough pressure with which to cook.  However, if you're not getting the performance you need, you should be prepared to take action.  One action might be to take some water out of the pot that you're heating and put it into the bowl that the canister sits in.  Don't get it too hot!  If you add just a touch of warmer water (slowly!) to the water that is already in the bowl, you will bring the water temperature up a bit and increase your stove's performance.  There are other ways to heat the canister, but liquid water is pretty safe so long as the canister never feels hot to the point of pain to the (unfrozen) bare hand.

Of course you can modify the stove to divert heat to the canister from the flame directly instead of using water, but there are risks in doing so. Be very careful.  Overheated canisters can and do explode.  A canister explosion is a potentially life threatening event.  ALWAYS  monitor the canister temperature with your (unfrozen) hand.  If the canister feels hot to the touch, turn it down immediately

Now you may be thinking, "if I can heat the canister, what's up with these planning numbers you keep talking about?  Shouldn't I be able to go as cold as I want so long as I keep the canister warm?"   Well, yes you can.  My planning numbers are an attempt to be conservative and thereby reduce risk (reduce, not eliminate).  The colder it gets, the harder it is to keep the canister warm.  If you're going out in really cold weather with a gas stove, think.  Can you really keep your canister warm in those temperatures?  What happens if the temperature is colder than you expected?  Can you compensate?  In really cold weather, your life may depend on your stove functioning.  Take no short cuts.

1.  If you use a canister right side up, the best cold weather fuel, propane, boils off at a faster rate, so you must be able to rely on the other components of your fuel.  Therefore choose isobutane and avoid n-butane.
2.  If you use a canister upside down (inverted), the propane stays in the mix and your fuel has better cold weather performance.  Most stoves cannot handle inverted operation.  Do your homework before trying this.
3.  If used upright, canisters experience significant cooling from within.  Therefore, it is the fuel temperature which matters, not the ambient temperature.  Your fuel temperature will be usually be colder than the surroundings after operating the stove for a while.
4.  If you use a canister upside down, the canister will not experience cooling (well, at least not to the degree that it does in upright operation).
5.  In order to have enough pressure to properly operate a stove, your fuel temperature must be warmer than the vaporization point (boiling point) of the fuel.  Generally, about 20°F/11°C degrees above the vaporization point will give you good operating pressure, but the actual performance of the stove is the bottom line.  Poor performance probably means that your fuel needs more heat.  Therefore you must be able to heat the canister.  Water is typically a safe way to heat the canister.
6.  NEVER heat a canister to the degree that it is painfully hot to the touch of an (unfrozen) bare hand.
7.  The higher you go, the colder the weather your gas stove will operate in, but the colder it gets, the harder it is to keep the canister warm, irrespective of elevation.  As you climb, temperatures fall faster than the performance of your stove increases.  You cannot out climb cold.
8.  If you heat the canister, you are not as constrained by the ambient temperature.  However common sense still applies here.  Can you realistically keep the canister warm enough in the temperatures expected?  What happens if the weather is colder than expected? What happens if a storm moves in?
9.  You must know and use the basics of cold weather canister operation (select good fuel, start with a warm canister, keep the canister warm, and heat the canister if needed). You must also be prepared for emergencies and the unexpected.

    Related articles and posts:

      Friday, November 25, 2011

      What's the Best Brand of Gas for Cold Weather?

      For warm weather (above 50°F/10°C), it doesn't much matter what brand of gas you buy.

      For cold weather, the brand of gas you buy does make a difference.  Typically, gas canisters contain some blend of propane mixed with either "plain" butane (n-butane) or isobutane. Some canister brands contain all three gasses.  For cold weather use, you generally want a canister with as little n-butane as possible.  Even though propane is the best cold weather gas, I'd take a canister with 10% propane and 90% isobutane over a canister with 30% propane and 70% n-butane.  Why?  Because the propane will burn off at a faster rate than the n-butane, leaving you with nothing but n-butane toward the end of your canister.  Butane is a poor performer in cold weather.

      Frozen lakes and snow, Sierra Nevada Mountains
      Why is butane a poor cold weather performer?  Why do we use blended gas?  Why don't we just use 100% propane?  That's all covered in my post on Gas Blends and Cold Weather Performance.

      How can we cope with cold weather?  For more info on canister stoves in cold weather, see:  Gas Stoves in Cold Weather – Regulator Valves and Inverted Canisters
      A frozen lake, Sierra Nevada Mountains
      What companies have got the best blend?  I don't have all the data, but here below is what I have.  This data is for the United States of America.  Brands and blends available elsewhere may vary.
      • Olicamp Rocketfuel is the best cold weather blend available in North America – at least based on the label.  It has 75% isobutane and 25% propane.  It's performance will not be radically better than an 80/20 mix, but Olicamp's 75/25 is a slightly better mix – if it is pure.  Any time there is isobutane, there will always be a certain percentage of plain n-butane present as well.  Here, quality control is essential.  Olicamp is not an actual stove company but is a brand name that distributes goods manufactured by others.  How committed is Olicamp to quality control?  How low is their percentage of crappy (for cold weather) n-butane?  I just don't know.
      • MSR is a good winter blend, 80% isobutane and 20% propane.  These numbers are confirmed on MSR's website.  MSR is pretty committed to the climbing and mountaineering community.  They are pretty committed to quality control.  I tend to trust MSR's numbers and believe that they have very low percentages of n-butane.  I generally go with MSR on my cold weather trips.  Your mileage may vary.
      • Jetboil is also supposedly 80% isobutane and 20% propane.  I have not been able to confirm these numbers.  Whatever the exact percentages are, it's an isobutane mix, so it should be reasonably good for cold weather.  How much n-butane does it contain?  I don't know.   No where will Jetboil put down in writing what their actual numbers are.  This tells me that their blend may vary a lot.  Jetboil wouldn't be my first choice simply because Jetboil will not commit, in writing, to any set of numbers.
      • Brunton is reputedly an 80/20 mix.  I have not been able to confirm these numbers.  Whatever the exact percentages are, it's an isobutane mix, so it should be reasonalby good for cold weather.  Again though, one has to ask what their commitment to quality control is.
        • Snow Peak is 85% isobutane and 15% propane.  These numbers are confirmed on Snow Peak's website.  I tend to trust Snow Peak's numbers more since they are willing to commit to them in writing.
        • Coleman Powermax is 65% regular butane and 35% propane.  These numbers are confirmed on Coleman's website.  Note:  This is for Coleman Powermax fuel only and is not for Coleman's regular gas canisters.  I wouldn't normally recommend a fuel containing regular butane (n-butane) for winter use, but Coleman Powermax is used in liquid feed mode, so the butane doesn't hurt anything.  Indeed, Coleman Powermax fuel is the best winter capable gas blend available in the United States.  Only the following three Coleman backpacking stoves can use Powermax fuel:  the Xpert, the Xtreme, and the Xpedition.  However, see:  Update on Powermax fuel 07 Nov 2011.

        BRANDS NOT RECOMMENDED* FOR WINTER USE (in no particular order)
        • Coleman regular threaded canisters (not Powermax) are 30% propane and 70% butane.  These numbers on on the side of the canister.
        • Primus is 25 % propane, 25 % isobutane, and 50 % butane per their website.  I suppose it's better than Coleman brand, but I'd still rather have a fuel with no regular butane at all.
        • Optimus brand is 25% propane, 75% butane, as printed on the side of the canister.  Since it contains regular butane, I wouldn't use it in cold weather.
        • Glowmaster is 20% propane and 80% butane per the side of the canister. 

        One caveat to the above:  If you're using standard threaded canisters in liquid feed mode (in other words, the canister is used upside down) or you're using a canister that is designed for liquid feed (e.g. a Powermax canister), the n-butane vs. isobutane issue matters less, although I would still generally prefer isobutane had I a choice.  In liquid feed mode, the liquefied gas stays blended and all of the fuels burn together at a constant rate.  With liquid feed, the propane does not burn off more quickly, and you're not left holding the bag with nothing but crummy (in cold weather) n-butane left.  In other words, with liquid feed, "regular" butane isn't such a bad thing provided that you've got plenty of propane content.

        For "normal" (canister right side up) use, avoid "regular" butane for cold weather.


        *Because they contain "regular" butane, a very poor fuel in cold weather.

        Related articles and posts:

        Thursday, November 24, 2011

        Gas Blends and Cold Weather Performance (Why not just use propane?)

        I got a good question recently:
        Hikin Jim, I see you refill [your backpacking canisters] with butane. What is the advantage over straight propane if propane works in lower temps? For that matter, why are these cartridges blended at all? I have wondered about this for a while.

        An excellent (and important) question. It has to do with vapor pressures. Take a look at the following boiling points table.
         Boiling point
        n-butane    -0.5C    31F
        isobutane    -12C    11F
        propane      -42C   -44F
        As you can see, propane will vaporize (boil) at extremely low temperatures whereas n-butane ("regular" butane) has a vaporization point some seventy five Fahrenheit degrees higher. Quite a difference!

        Let's say you have liquid propane in a container and the ambient temperature is a nice, comfortable 75F (24C). 75F is some one hundred nineteen degrees (Fahrenheit) above the boiling point of propane. Propane at that temperature desperately wants to boil and exerts tremendous vapor pressure against the walls of the tank, vapor pressure so strong that you need a fairly heavy steel container to hold it safely, such as those found on the big green 16.4oz (~460g) propane canisters from Coleman. The little lightweight canisters that backpackers carry could literally turn into a hand grenade at those pressures.

        On the other hand, n-butane is relatively benign at those temperatures. Take a look at a clear plastic lighter some time. That clear liquid inside is n-butane. Yep, all that's needed to contain n-butane is some flimsy plastic. Contrast that with a 16.2 ounce Coleman canister! Of course the problem with n-butane is that if the fuel temperature falls below about 40F/5C, the vaporization isn't strong enough to run a typical gas stove.

        Well, if propane is great but would catastrophically burst a backpacking canister and n-butane is easily contained but useless in cold weather, what to do? Well, you blend the two. The liquid blend takes on properties that lie somewhere between low pressure n-butane and high pressure propane. Better still, you get a chemist to rearrange the internal structure of the n-butane molecules a little and create isobutane. Isobutane is what is known as an isomer of butane. It's the same stuff, but the internal components have been put into a different arrangement, an arrangement that in this case works in our favor in that the boiling point drops by twenty degrees Fahrenheit! Nice, eh? It's like re-packing the trunk of your car. It's the same stuff, but in a different order. In the case of your car's trunk, things fit better. In the case of butane, the properties change a bit, and we've got a better cold weather fuel. The best cold weather blend for upright canister stoves is therefore isobutane mixed with propane. Note that I stressed the word "upright." More on that in a minute (see the second of the two below links).

        The problem with this blending arrangement is that the higher pressure propane tends to boil off a bit faster than than the n-butane or isobutane. Toward the end of the life of the canister, all you have left is the "lesser" (in terms of cold weather performance) of your fuels. This is one reason why in cold weather you can get the dreaded "canister fade" where your flame slowly fades out toward the end of the life of your canister, and you can't operate your stove even though, when you shake the canister, you can still hear fuel sloshing around in there.

        There are two things you can do to get good performance and avoid canister fade in cold weather.  One, you can take action to warm the canister or two you can switch to a liquid feed gas stove.

        With respect to liquid feed gas stoves:  If gas is kept under sufficient pressure, it liquefies, i.e. the form of the fuel changes from a vapor into a liquid.  If you feed the fuel in liquid form to your stove, you no longer have to worry about which fuel in your blend has a tendency to boil off faster into a gas.  With liquid feed, the blend you start with is the blend your finish with.  Since the blend doesn't change with liquid feed, it's not quite so critical that the non-propane component of your fuel be isobutane.  Again, since the blend doesn't change, the cold weather performance of your fuel is just as good at the end of your canister as it was at the beginning, and you don't get such pronounced "canister fade" toward the end of the canister.

        There are a lot of advantages to using a stove in liquid feed mode in cold weather, but be aware that not all gas stoves can be used in liquid feed mode.   Be sure to read the above linked article to find out what type of stove may be used safely.  You also need to buy the right brand of gas in order to get good cold weather performance.  Not all brands are equal.  For more information, please see my post on What's the Best Brand of Gas for Cold Weather?

        As for refilling backpacking canisters, butane is cheap, readily available, and of lower pressure than the original contents (and therefore reasonably safe). Although reasonably safe, the one problem with refilling backpacking canisters with 100% butane is that they're no good if the fuel temperature gets much below about 50°F/10°C.  So, I just use my refilled canisters on fair weather trips.  I tend to prefer fair weather trips anyway, so refilling backpacking canisters works very well for me.  YMMV.  :)  I wish I had a source of cheap isobutane, but alas I do not. Refilling with 100% isobutane would also be reasonably safe if the canister originally contained a propane-isobutane blend. Refilling a backpacking canister with 100% propane could be a very deadly enterprise and should be avoided. But this post is really about why we blend gas and why we don't use 100% propane in backpacking canisters.  At some future point, I'll dedicate an entire post to the subject of refilling canisters.

        Hope that clears things up a bit.


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        Wednesday, November 23, 2011

        Hexamine (ESBIT) Stoves

        Hexamine (such as ESBIT brand) stoves are very interesting.

        Ultralight hikers prize them for their light weight, but they can be a nice addition to any kit as an emergency stove. They've got about the most stable fuel around. The fuel doesn't evaporate or go bad. You can generally burn 40 year old fuel that hasn't been sealed without problems. I keep mine sealed and protected (they can be crushed or chipped pretty easily), but I've seen some old hexamine fuel that burned just fine. They're great for long term storage in a kit that you don't plan to touch often.

        The down side is that they don't put out a lot of heat, can be hard to light (particularly in wind), and the low velocity flame really needs a windscreen. They also leave a residue on the bottom of your pot.  I usually keep my pot in a plastic bag if I'm going to be burning hexamine.

        One trick for lighting them is to set the tablet on the edge of the stove at first. Get your flame under the tablet. Once it's lit, then move it to the center of the stove with a stick or something. This trick is a little easier with the larger ESBIT brand rectangular tablets than the smaller "pill shaped" tablets that some companies produce.

        Hexamine's not bad stuff, but it's not particularly powerful either. It's worth playing with it a few times in order to get used to its quirks. Don't set it down in the bottom of your pack untried and then expect to pull it out and be comfortable with it out on the trail. It's no big deal, but it's worth getting used to how to light, how to cook with, how to extinguish, etc. before you head out.

        Despite the fact that hexamine is not volatile, hexamine is not permitted on airline flights. Hexamine is a precursor to explosives such as RDX/Cyclonite. You wouldn't want to go into an airport with the scent of hexamine about you.


        Friday, November 18, 2011

        A Look at the Trangia Alcohol Burner

        People have asked me what I think about the Trangia burner in and of itself.
        A Trangia alcohol burner
        I think the Trangia burner is a good one. It's meant to be used in conjunction with other components, but if we consider the burner alone for a moment:
        1. It's brass. Can you say solid? Yeah, you can still break them, but the chances of it crushing in your pack are pretty much nil unless you fall off a cliff or something (in which case you probably have more to worry about than what shape your burner is in). ;)  Brass conducts heat well which is an advantage in cold weather where alcohol sometimes can be difficult to vaporize. Titanium burners, while lighter, do not conduct heat well.
        2. It's an open design. You just pour your alcohol in. To light it, you flip in some sparks with your fire steel or use a lighter or match. The point being that it's really easy to work with. There are some alcohol stoves where you've got to get the alcohol in a tiny little hole, and you have to prime them even in warm weather, all sorts of fiddly stuff like that. No thanks. The Trangia burner is a practical, easy to use burner.
        3. The Trangia burner is a nice balance between speed and efficiency. The Trangia isn't the fastest out there -- but that's a good thing. The faster burners tend to eat through your alcohol which means you're running out of fuel when the guy next to you still has a couple of days supply of fuel. Yet on the other hand they've got enough power that they aren't at the mercy of the slightest breeze. Some really efficient burners are such low power burners that unless you set the windscreen up perfectly, your pot will never boil.
        4. The Trangia burner has a lid that can be sealed. Ever try to get left over alcohol out of a burner? It's a pain in the butt. Most guys either burn it off (i.e. waste it) or manage to recover only a portion of it (again, wasted fuel). With the Trangia burner? No problem. Just seal it up. Next time you need the burner, it's already fueled. As a precaution, I put my burner inside a Ziploc bag, sometimes two. They do leak a few drops some times.
        The lid of a Trangia burner has an "O" ring which forms a tight seal so that alcohol can be carried in the burner

        5. The Trangia burner can simmer when the simmer ring is used. Relatively few alcohol stoves can really simmer. Simmering means you can cook real food not just "boil in a bag" type meals.
        The simmer ring of a Trangia burner (sitting in a pan).  The "door" can be nearly shut to get a low  flame or completely shut to extinguish the stove.
        So, you've got a really solid burner that conducts heat well, that is practical and easy to use and is a balance between speed and efficiency that can be sealed so you don't waste fuel that can simmer. That's a half a dozen reasons why the Trangia is one of the most popular alcohol burners out there and why so many systems are built around a Trangia burner (Clikstand, Trangia Triangle, WestWind, plus dozens of home made ones).  For the weights of each component, please see the Technical Appendix below.

        It's a good burner.


        Related posts and articles:
        Technical Appendix (with weights of all components)
        • Trangia Burner:  67g/2.4oz
        • Trangia Burner Lid:  21g/0.7 oz
        • Trangia Burner Simmer Ring:  23g/0.8oz
        • Total Trangia Burner Weight:  112g/4.0oz

        Tuesday, November 15, 2011

        Cold Weather Tips for Alcohol Stoves

        I can recommend at least four "tricks" for alcohol stoves in cold weather:
        1. Keep your alcohol in a coat pocket or somewhere where it will stay warm.
        2. Use methanol such as comes in the yellow bottle of HEET that can be purchased at Walmart, auto parts stores, etc. Methanol generally has a higher vapor pressure than denatured alcohol and will work better in cold. DON'T drink methanol, don't breath the fumes, and don't get it on your hands. Methanol is toxic and can lead to severe neurological problems, blindness, and death. Yipes!  But if you're safe how you pour and burn, it's no big deal.  Don't be intimidated; just be careful.
        3. Use a priming pan. I use the lid from an old tin of tea. The lid is slightly bigger in circumference than my stove.  Put the lid underneath your stove. Pour some alcohol in the priming pan and ignite. The alcohol in the priming pan will warm the stove and provide for faster vaporization.
        4. Insulate! Put something like some closed cell foam cut from an old backpacking pad under the stove. You don't want snow or cold ground sucking the heat out of your stove. I wrap my closed cell foam in duct tape to a) protect the foam and b) prevent spills from getting into the foam which could catch fire while operating the stove. Don't ask me how I know that last bit. ;)  On top of the foam, I set a circular cut out of approximately 36 ga. aluminum sheet on top of which I set the alcohol stove.  The little circle of aluminum helps diffuse the heat so you don't screw up your duct-tape wrapped pad.
        Got other tips?  Please send 'em my way. 


        Related posts and articles:

        Monday, November 14, 2011

        Stove of the Week: The Trangia 27

        Let's say you wanted a reliable stove.  A really reliable stove.  A stove where there's nothing to go wrong.  A stove that's going to work in any conditions, no matter what.

        What's  that?  It's a trick question?  No, there really is such a stove, the Trangia.  The Trangia alcohol stove system is, simply put, the most reliable backpacking type stove in the world.
        A Trangia 27
        Now here's the funny thing about what is possibly the world's most reliable backpacking stove:  It's relatively unknown in the United States.  Alcohol stoves have long taken a back seat in the American outdoors scene.  However, in the last decade or so the ultralight movement has swept over American backpacking, and alcohol stoves have exploded on the scene with a vengeance almost as though making up for lost time.
        One little problem for the Trangia:  it's hardly ultralight.  So, even though alcohol stoves are all the rage in the US backpacking community right now, you may not see more of the complete Trangia system, at least in the US.  I am seeing the excellent Trangia burner used in a variety of configurations including the excellent Clikstand set up.  Internationally though, the Trangia has an enduring reputation for reliability and the ability to function under any conditions.  The Swedish call it a stormkök -- storm cooker.  The name says it all.  Though the Trangia is a bit bulky and heavy, particularly for an alcohol stove, there are many who swear by it and will bring nothing less into the back country.

        Somewhat unusual for an alcohol stove, the Trangia is actually able to simmer with the use of a "simmer ring" (see more below).  The Trangia is therefore an alcohol stove that one can do real cooking on and not merely just boil water.

        The Trangia stove system came out in 1951.  Rather than replicate here what is more than adequate elsewhere, I provide you with the following link on the history of the Trangia company for those who are interested.

        There are three basic models of the Trangia:
        The Trangia 25, which comes with 1.75 L and 1.5 L nesting pots and a 22cm diameter fry pan/lid and is intended for three or four people.
        The Trangia 27, which comes with two 1.0L nesting pots and an 18cm diameter fry pan/lid and is intended for one or two people.
        The Trangia 28 (aka the "mini Trangia"), which comes with one 0.8L pot and a 15cm diameter fry pan/lid and is intended for solo use.

        The Trangia 25 and 27 are essentially the same stove except that the 25 is larger and the 27 is smaller.  Models 25 and 27 are complete in and of themselves and need no additional components in order to function well.  The Trangia 28 (the "mini Trangia") needs a windshield (not included) in order to function well.

        Models 25 and 27 are available in "ultralight" aluminum or hard anodized aluminum.  Several configurations of models 25 and 27 are available.  The configurations include such things as non-stick coatings and an optional tea kettle.  I won't try to list all of the possible combinations, instead, I encourage you to head on over to the Trangia website where all possible combinations are listed. There is only one configuration available of model 28.  The alcohol burner is the same across all models and configurations of Trangia stoves.  An optional gas burner is available for some configurations of the Trangia as is a multi-fuel burner.

        Now, then, this week's stove is the Trangia model 27.  My model 27 Trangia was built in the late 1970's or thereafter but prior to 1988 based on the information provided at the above history link.  Today's Trangia 27's are nearly identical to mine but do have some differences such as a lighter weight modern alloy and openings for use with a gas burner.

        So, let's have a look at this famous stove. The Trangia 27 consists of six main components:  A lower windscreen/base, an upper windscreen, two pots, a lid, and a burner.  The Trangia also comes with a strap to hold everything together and a pot gripper/pot lifter.

        One of the wonderful things about the Trangia is that all of the components nest together in a nice package.
        All of the Trangia 27's components fit neatly together.
        A strap secures everything together.  This strap is of the period but is not original and is not a Trangia product.
          Let's take a look at what's inside the package.
        A Trangia 27 with the lid off but still all nested together.
        Inside my Trangia 27, I carry the burner, a lighter, a pot gripper (not original), and a fuel bottle.  There's also room for a spoon, tea bags, or other items.
        A closer look at the contents of my Trangia 27
        Now let's take a look at the base (lower windscreen) of the stove.  Note how there are ventilation holes on one side of the lower windscreen but not the other.  Note also the air holes that surround the large central hole.  These air holes are a key component in the Trangia's design and what allow it to function in heavy winds.
        The base (lower windscreen) of a Trangia 27.
        Take a look at this diagram of the air flow within a Trangia stove.
        A diagram of the air flow within a Trangia stove system.
        The air holes in the lower windscreen are faced into the wind.  The air is then forced up around the burner in a controlled fashion.  The wind acts just like a bellows, oxygenating the burner.  The air is heated by the burner.  The heated air is forced up through the gap between the upper windscreen and the pot.  The narrowness of the gap prevents too much air, air that might rob the system of heat, from flowing through.  The air that does flow through is forced to stay close to the pot which increases heat transfer.  In short, you've got a very efficient stove capable of operation in heavy winds.

        The burner mounts in the base.
        The Trangia burner mounted in the Trangia base.
        The upper windscreen is then emplaced on top of the lower windscreen. 
        Upper Trangia windscreen mounted on lower windscreen
        Note in the photo above that the put supports are flipped up into the "up" position.  When the put supports are in the "up" position, the lid may be used as a fry pan.
        A Trangia 27 in frying mode
        A Trangia 27 with the pot supports flipped up

        A Trangia 27 with the pot supports flipped down.
        With the pot supports down, a pot fits neatly inside, suspended at the ideal height above the burner.
        A Trangia 27 with a pot in place.
         Now, let's take a look at the two pots.  The two pots nest neatly within one another.
        The two pots of a Trangia 27 nested together.
        The two pots of a Trangia 27 separated.
        The two pots fit together only one way.  They both have the same volume, but one is tapered differently than the other.  Put the more tapered pot on top, and it nests neatly in.  Put the more tapered pot on the bottom, and the two pots stack in such a manner that both pots can be used simultaneously.  Ingenious!
        The two pots of a Trangia 27 in stacked one atop another ready for simultaneous use.
        One of the pots is inscribed with volumetric markings.  Wisely, the markings can be read not only from the outside but from the inside of the pot.
        One of the pots has 0.3 L and 0.5L markings.
        With a pot in place, the lid fits neatly on, sealing in the heat.
        A Trangia 27 fully set up, with one pot.
        It doesn't look quite as neat with two pots, but we're here to cook, not look good, yes?  We could even turn the lid over and cook some meat balls or something in the lid while the pasta cooks in the bottom pot and the sauce warms up in the top pot.  Pretty slick!
        A Trangia 27 fully set up, with two pots in place.
        OK, so now let's take a look at the burner.  The burner consists of three pieces:  A simmer ring, a lid, and the burner itself.  Only the burner itself is required.  The lid and the simmer ring may be left behind if so desired.

        The simmer ring is a ring shaped piece of brass that fits over the burner.  Attached to the ring is a "door" that can be slid back and forth opening up or restricting the burner which causes the flame to correspondingly increase or diminish.  When you want to extinguish the flame completely, simply close the simmer ring door completely.
        The simmer ring of a Trangia burner.
        A simmer ring in use on a Trangia 27.  Can you spot the flame?
        The lid of the Trangia burner is threaded such that it forms a relatively tight seal on the body of the burner.  A rubber "O" ring is emplaced at the end of the threads so that a really good seal is made.  Because of the "O" ring, alcohol can be carried in the stove.  So, if at the end of cooking you still have alcohol left inside the stove, no worries, just leave it there.  There's no need to go through the hassle of trying to drain the stove.  Simply let the stove cool and cap the stove.  Off you go with no hassle.  Be sure to let the stove cool first before putting on the cap or you'll melt the "O" ring.  DO NOT use the cap to extinguish the stove. You'll melt the "O" ring for sure if you use the cap to extinguish the stove.  Use the simmer ring to extinguish the stove.  If you've left the simmer ring at home, you could yank the "O" ring out of the cap and then extinguish the stove, but that's a bit of a hassle.  If you do melt the "O" ring, not to worry.  Replacements can be had easily, and your stove will still work without an "O" ring (or without the entire lid for that matter).
        The lid of a Trangia burner.  DO NOT use the lid to extinguish the flame.
        As for the burner itself, the Trangia burner is an open jet style of burner.  The open style of the burner means that it's very easy to add fuel; simply pour it in.  Except in cold weather, no priming is required.  Simply apply a flame from a match or a lighter to the center of the open cup, the alcohol will ignite, and the stove will prime itself.  In no time at all, the alcohol will be hot enough to vaporize, vaporized alcohol will be coming out the jets, and the stove will be up and running properly.
        A Trangia burner.  Note alcohol inside the burner.
        The Trangia burner is a good compromise between speed and efficiency.  The Trangia burner is not the fastest alcohol burner out there in terms of boil times, but faster isn't necessarily better.  Faster burners tend to require more alcohol to do the same amount of boiling.  A more efficient burner like the Trangia means that you don't have to carry as much fuel.  But the Trangia is by no means slow.  As I say, the Trangia strikes a very good balance between efficiency and speed.

        A Trangia 27 just after being lit.  Note flame (a bit hard to see)
        As I have said, the Trangia is no slouch when it comes to boiling up water.  It's not a gas or liquid fuel stove, but it takes only a minute or two longer than petroleum fueled stoves.
        Passing the "tea test" on a Trangia 27.
        Water boiling on a Trangia 27
        Now, of course, the whole point of a stove is to have a warm refreshing beverage or something nice and hot to eat.
        Cooking oatmeal on a Trangia 27
        My assistant seems to be getting the point, don't you think?  :)
        My assistant is ever so helpful when it comes to the eating portion of my stove hobby.  :)
        The Trangia stove:  Good to the last drop.
        Good thing I brought an assistant.  ;)
        I hope you've enjoyed this Adventure in Stoving.


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