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Sunday, September 14, 2014

Which is Lighter – Alcohol or Gas?

The "prevailing wisdom" seems to be that canister gas is lighter than alcohol on longer backpacking trips.  On the surface, this would seem to make sense.  From a chemistry standpoint you have to carry roughly twice as much alcohol (assume 50/50 methanol/ethanol) as gas to produce the same amount of heat.  Even though alcohol containers are lighter than gas canisters, you have to carry so much more fuel, at some point the greater amount of fuel you carry for an alcohol set up will exceed the weight of an equivalent canister gas set up.  Or so the thinking goes.  But is it true?
Time to head into the backcountry.  Uh, hope your heavy pack doesn't ruin your trip.  But what's really lighter?
So, which is actually lighter – alcohol or canister gas?  Well, let's "do the math" and see what we come up with. I'll do three comparisons of gas stoves against alcohol as listed below.
  1. Conventional canister stove vs. alcohol
  2. Jetboil canister stove, typical use, vs. alcohol
  3. Jetboil canister stove,  "gram weenie" (minimalist) use, vs. alcohol
I'll cover conventional canister stoves vs. alcohol in this post.  I'll cover high efficiency stoves (i.e. a Jetboil) in future posts.

Conventional Canister Stove vs. Alcohol
OK, so what do I mean by "conventional" canister stove?  I'm talking about just a regular upright canister gas stove and a plain pot, the kind that does not have a heat exchanger.  In other words, just an ordinary gas stove with a plain pot.  Examples would include an MSR Pocket Rocket and a Snow Peak Gigapower.  Let me put up the numbers first, and then I'll walk you through them.  For the sake of brevity, I'm going to limit my projections to 14 days.  I'm assuming that most people don't do trips longer than two weeks without re-supplying.  I have numbers if you're interested that go out to three weeks. I'll discuss how to request those numbers later on in this post.

An ultralight conventional canister gas stove
Here are the numbers:
ALCOHOL
Number of days on trail 1 2 3 4 5 6 7 8 9 10 11 12 13 14
ml of alcohol per day 50 50 50 50 50 50 50 50 50 50 50 50 50 50
Total ml of alcohol 50 100 150 200 250 300 350 400 450 500 550 600 650 700
Specific gravity 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
Total grams of alcohol 40 80 120 160 200 240 280 320 360 400 440 480 520 560
Fuel bottle weight (grams) 18 18 32 32 32 45 45 45 45 45 45 63 63 63
Stove system weight 60 60 60 60 60 60 60 60 60 60 60 60 60 60
Total grams (bottle + fuel + stove) 118 158 212 252 292 345 385 425 465 505 545 603 643 683
Weight carried end of trip (grams) 78 78 92 92 92 105 105 105 105 105 105 123 123 123
CANISTER GAS
Number of days on trail 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Grams of gas per day 20 20 20 20 20 20 20 20 20 20 20 20 20 20
Total grams of gas needed 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Actual grams of gas carried 110 110 110 110 110 220 220 220 220 220 220 330 330 330
Canister weight (grams) 100 100 100 100 100 140 140 140 140 140 140 240 240 240
Stove system weight 60 60 60 60 60 60 60 60 60 60 60 60 60 60
Total grams (can + fuel + stove) 270 270 270 270 270 420 420 420 420 420 420 630 630 630
Weight carried end of trip (grams) 250 230 210 190 170 300 280 260 240 220 200 390 370 350
Number of days on trail 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Start of Trip Difference (grams) 152 112 58 18 -22 75 35 -5 -45 -85 -125 27 -13 -53
Start of Trip Difference (ounces) 5.4 4.0 2.0 0.6 -0.8 2.6 1.2 -0.2 -1.6 -3.0 -4.4 1.0 -0.5 -1.9
End of Trip Difference (grams) 172 152 118 98 78 195 175 155 135 115 95 267 247 227
End of Trip Difference (ounces) 6.1 5.4 4.2 3.5 2.8 6.9 6.2 5.5 4.8 4.1 3.4 9.4 8.7 8.0
Average Difference (grams) 162 132 88 58 28 135 105 75 45 15 -15 147 117 87
Average Difference (ounces) 5.7 4.7 3.1 2.0 1.0 4.8 3.7 2.6 1.6 0.5 -0.5 5.2 4.1 3.1

OK, so let's talk about the numbers.  These numbers are for a solo stove user.  Use of a single stove by multiple persons would require an adjustment to the above numbers.

The first line for each type of stove is the length of the trip.  The trip is assumed to be "unsupported".  In other words, you aren't going to pick up supplies anywhere along the way during the trip.
"Unsupported" trips occur in areas where resupply is infeasible.  All supplies must be packed in.
Now, we need to know the total weight for each set up.  The total weight is the sum of the weight of the fuel + the weight of the stove set up + the weight of the fuel container.  Assume for these purposes that we use identical pots.

In the Alcohol section, I go through some gyrations to calculate the weight of how much fuel I think I'll need.  We can argue exactly what is the correct value for the specific gravity of SLX denatured alcohol (which is what I've been using lately), but the important point is that the weight of alcohol is double that of canister gas.

Now, look at the two stove set ups.  I'm allotting 60g each for both alcohol and canister gas.  I include the weight of a full windscreen with the alcohol stove set up.  I consider a windscreen essential to the efficient burning of alcohol.   Now, can you find a canister stove that is lighter than 60g?  Certainly.  And you can also find an alcohol set up that is lighter than 60g.  For these purposes, let's assume that the two stove set ups weigh the same.

The container weight will vary with the amount of fuel that we use.  More fuel will require a larger container or multiple smaller containers.  In this comparison, I'm going to assume that people are going to take full canisters at the start of the trip, a fairly standard practice.  In the "gram weenie" (minimalist) comparison, I'll use partial canisters to see what kind of weight savings I can obtain.  See Appendix I for a list of the specific sizes and weights of the containers used.

At this point we've got the total weight of each set up for each length of trip, from 1 to 14 days.  But that weight is the weight you show up with at the trailhead at the start of the trip.  Recall that during the trip, you'll be burning the fuel.  The weight you show up at the trailhead will not be carried throughout the trip.  So, below the "total grams" line I show the weight at the end of the trip after you've burned the fuel.

Next, I show the difference in weight between alcohol and gas at the start of a trip.  Negative numbers indicate the weight savings if gas is used.  Positive numbers indicate the weight savings if alcohol is used.  Notice that for trips up to 4 days in duration, alcohol is lighter but that on the 5th day, gas is lighter.  This seems to fit the "prevailing wisdom" that gas is lighter for longer trips.  But now notice that on a 6 day trip, alcohol reverts to being lighter.  What happened?  Well, on a six day trip, we use 120g of fuel.  A small canister only holds 110g of fuel.  We switched to a 220g canister, and now we're carrying more weight in both fuel and container.  As the duration of a trip lengthens, we again see weight savings for 8 through 11 day trips.  A 12 day trip shows up with alcohol being lighter again because we had to switch to a 220g canister and a 110g in order to have enough gas.  And so on.

But these are starting weight differences.  The next set of rows shows ending weight differences.  Now here's something a bit startling:  alcohol set ups are always lighter by the end of the trip.  Why?  Well, container weight.  Take a look at Appendix I.  With a 110g size gas canister, for example, the canister weighs almost as much as the fuel.  That steel canister is still with you at the end of the trip. With alcohol, the weight is almost all fuel.

Lastly, there is one final set of rows in my comparison table:  Average difference.  Here, I'm averaging the starting and ending difference in weight between alcohol and canister gas.  Notice here that in only one instance, at eleven days (highlighted in green), is canister gas lighter on average than alcohol.
Preparing Ramen with mixed vegetables and turkey jerky on an alcohol set up.

Commentary
Now, ending light may not always be your chief goal.  When is you pack heaviest?  At the start of a trip, when you've got all your food.  So, having a lighter stove set up at the start of the trip is actually a good thing, and therefore a gas set up might be in order.  However, that said, it's only on longer trips, 10 and 11 days long, where anything even close to real weight savings occur, about 1/4 of a pound.  The start of trip weight savings when using a gas stove on longer trips are fairly modest, at least with conventional stoves.  I'll discuss results with a high efficiency stove (i.e. a Jetboil) in two future posts.

The biggest drawback to gas stoves is those heavy steel canisters.  The best you can do in terms of a fuel to container weight ratio is about 2:1.  With alcohol you can get a ratio as good as 10:1.  An important goal in trip planning when using a gas stove is to minimize canister weight.

Minimizing canister weight
First, never carry two smaller canisters when a single larger one will do.  Your fuel to canister weight ratio is always better with a larger canister.  In cases where you need more than 220g but less than 331g of fuel, you'd actually do better weight wise with a 450g size canister that has had some fuel burned off than you would carrying two canisters (i.e. a 110g size and a 220g size).  If you're planning a trip where you just barely have to move up to the next larger sized canister, you might want to plan a stoveless meal or two or bring a more efficient stove just so you don't have to bump up to that next larger canister.  In short, always strive to bring only one canister, the smallest, lightest one that has enough capacity for your trip.  Try not to have to bring two canisters or to have to move up to the next larger size.
In the interests of saving weight, always carry the smallest sized canister you reasonably can.
HJ, your numbers stink!
Don't like my numbers?  No worries.  You can have my spreadsheets and plug in your own numbers.  Write me at Hikin dot Jim using the domain Gmail dot com and ask for a copy.  Note that there is no "g" in "Hikin".  Hopefully, I won't get inundated here.  I have this in Excel 2010 format.  If you need an earlier format, please let me know, and I'll do my best.

Conclusion
So, in conclusion, with a conventional upright gas stove, gas can be lighter at the start of a trip, but alcohol is always lighter by the end of a backpacking trip.  In terms of the average difference in weight throughout the trip, alcohol is almost always lighter.  If you're looking to save weight, alcohol stoves are a pretty good bet.

I hope all these calculations are of some help to those looking to lighten up,

Thank you for joining me,

HJ


Appendix I – Weights
Empty canister weights.  I weighed several different brands of canisters on my gram scale.  There is some variability among brands in both content and canister weight, but I'm going to use the below weights which I think are representative.  I use the word "ratio" below but only list one number for brevity's sake.  Mentally, just include ":1" after each number shown below.
1.  A 110g size canister weighs 100g when empty.  Fuel to container weight ratio = 1.1
2.  A 220g size canister weighs 140g when empty.  Fuel to container weight ratio = 1.6
3.  A 450g size canister weighs 210g when empty.  Fuel to container weight ratio = 2.1

Empty alcohol fuel bottle weights.  I weighed some of the alcohol bottles I have lying around.  There may be lighter versions available, but let's use the below numbers in our calculations.  I use the word "ratio" below but only list one number for brevity's sake.  Mentally, just include ":1" after each number shown below.
1.  A 125ml fuel bottle weighs 18g when empty.  Fuel to container weight ratio = 6.3
2.  A 250ml fuel bottle weighs 32g when empty.  Fuel to container weight ratio = 7.0
3.  A 500ml fuel bottle weighs 45g when empty.  Fuel to container weight ratio = 10.0


Appendix II – Assumptions
  • The first assumption is of course that alcohol stoves will work for your style of stove use.  If you're doing gourmet cooking or cooking for a group of three or more, then an alcohol stove may not work for you.
  • Gas to alcohol fuel weight ratio is 2:1.  In other words, you need to burn twice the alcohol by weight to get the same amount of heat as you would from gas.  Yes, I'm assuming 20g/day for gas and 50ml/day for alcohol, but the amounts are not so much what is important; it is the ratio that is critical.
  • 6 cups (approx 1.5L) of water boiled per day.
  • Water temperature approx. 10C.
  • Very little simmering.
  • Efficient alcohol set up (I used a Caldera Cone from Trail Designs to develop my numbers).
  • Gas stove is used efficiently (turn it down, use a lid, use a wide enough pot, etc.)
  • Stoves are reasonably shielded from wind.
  • Regular canister stove (not a Jetboil, a Reactor, or similar).
  • Plain pot (no heat exchanger).
  • Air pressure approx 900 mBar.
  • The same pot is used for both alcohol and canister gas.
  • Gas and alcohol stove set ups are of equal weight.
  • A windscreen is included in the weight of an alcohol stove set up.
  • No resupply (at least of fuel) occurs during the trip.
A windscreen is essentially mandatory on alcohol set ups like this Bobcat set up from Flat Cat Gear.



18 comments:

  1. Thanks Jim for taking the time to assess the difference and then to post it. Much appreciated.

    ReplyDelete
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    1. You're welcome, Alan. I've got two more installments that I want to publish, hopefully by the end of the month. Then I want to compare a Jetboil with a conventional gas stove. Stay tuned.

      HJ

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  2. I'm forced to the conclusion that alcohol is lighter, primarily because of the weight of the container. For the long distance hiker in the US, who is resupplying every few days, alcohol is an obvious choice because of wide availability. Yellow HEET is very convenient because it comes in a small container and can be purchased at any auto parts store. Canister fuel may be available on established trails, but is not common where I live. The closest available is probably twenty five miles away. My preferred canister stove for cooking is my modified Roberts Mini Stove. My preferred canister stove for heating water is the Jetboil. I use either a Starlyte style alcohol stove or a cat food can stove inside a modified Jim Wood Fire Bucket windscreen. Skewers support my pot, which can be a heat exchanger pot or a plain pot. This system supports the use of a tea candle in a cat food can which can be used for simmering. The question that I have to answer is whether I want to cook or just heat water. In most cases, I just want to heat water.

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    1. Hi, Bill,

      So many stoves so little time. :)

      I'm actually able to do some pretty good backpacking type meals using a simmer ring on my alcohol stove. I make simple meals -- simple but better than freeze dried. Rice, noodles, things like that. I use alcohol on all my solo backpacking trips because it is so much lighter -- and the chance of a mechanical failure is almost zero.

      HJ

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    2. I've made some simmer rings for my Starlyte style stove, but have yet to cook with them. They are easy to make and appear to work well. I seldom ever use freeze dried prepackaged food, preferring to make my own. I do pre-cook and dehydrate some foods. I just made some bean bark.

      I hope that your job situation has settled down. I hadn't planned to retire, but things happen. After seven months of retirement, I'm joining the folks who wonder how they had time to work.

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    3. Well, congrats on retirement. I'm still at least 15 years away unless something odd happens. I would have no problem filling the time were I to retire! The job is doing OK. Been with the present company for about a year. There's a layoff coming though, so anything could happen.

      HJ

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  3. Bill mentioned the availability of fuel, and you mentioned that "the chance of a mechanical failure is almost zero," which sums up two of the absolute best things about alcohol stoves!!

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    1. Randy,

      The mechanical reliability and zen-like silence of alcohol stoves is something I really like. Plus I don't have to landfill any steel canisters. I just refill my alcohol bottle and go.

      On the AT, I've heard alcohol is pretty easy to come by. I'm not sure how easy it is on the PCT, although any town with a gas station would probably have some form of alcohol available. It's the little places like Red's Meadow and the like that I'd be worried wouldn't have alcohol. I guess you could always use wood as a back up, particularly if you have a set up that will support both wood and alcohol AND do it well.

      HJ

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    2. The only real drawback to alcohol is the nearly invisible flame and the and the possibility of tipping the stove and having a fuel spill that causes a fire. I like the stove that I made because the alcohol is absorbed in a ceramic fiber filling. Even so, I like to have a little pan to set the stove in that fits inside my windscreen. This stove is so small that a mini cat food can stove can be used as a snuffer.

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    3. Bill,

      I always check my stove with my hand. If I feel heat, I don't add fuel. No problems as yet. I keep meaning to try a pinch of salt in the alcohol. It should burn more yellow with sodium in the mix. Haven't tried it yet.

      Yes, you could spill alcohol, but then again, white gas stoves can be over-primed or leak and canister gas stoves can have a valve jam open when the canister is removed. I've had all these things happen. They can all be quite dangerous. I don't think alcohol stoves are significantly more dangerous than other types of stoves, but then again I haven't burned myself yet (thank God).

      HJ

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    4. I think that most of us that regularly use these stoves are pretty diligent. I've never had a serious incident with any of my stoves, but I know that the potential is there. The trickiest time with my alcohol stove is right after I light it. I can't easily see the flame and the heat has yet to build up. I don't use my white gas stoves much anymore, but I remember checking the O-rings and gaskets for leaks before lighting up. The flames on white gas and canister stoves are often hard to see in the sunlight. The roarer burner had the advantage of making a lot of noise while it was burning. The one thing that still concerns me on the upright stoves is the inherent instability if you don't have a good solid flat surface for the stove. One of my favorite stoves of all time was the Coleman Peak One Apex 2 which had a tripod base and a low center of gravity. Alas. it was a bit on the heavy side.

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    5. Just knowing what the dangers are is half the battle. I think the number of wildfires caused by stove accidents is fairly low. Not zero, but fairly low. Open campfires are far more likely to cause a wildfire, particularly if not properly extinguished.

      I have an Apex II, and it's a nice stove. I probably won't be taking it on any serious backpacks any time soon; it's too heavy and bulky, but it's a good cooking stove with a very stable surface.

      HJ

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  4. Very useful post. You have inspired me to make my own comparison table using your "live" fuel estimates and assumptions. This is a nice tool to compare own and wish-to-have stoves. Next I need to figure out if your estimates are valid for my use.

    Looking forward to see your comparison with Jetboil-type stoves.

    Cheers

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    1. Hi, Stefan,
      You're welcome to a copy of the Excel spreadsheet if you would like to have it. I'm always interested in what other people are thinking, so fee free to post comments based on your numbers.

      HJ

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    2. Yes, I would like a copy of your spreadsheet. Please send it to bondejacobsen at gmail dot com. That is if you can, as the mailer-daemon tells me that delivery of my email has failed permanently. I guess you have grown so popular the mailbox has overflown.

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    3. My email is overflowing? Really? Hmm.

      Let me have a look. It will probably be a couple of days; I'm heading out to the backcountry for the weekend.

      HJ

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  5. Thanks for putting in the time and effort to crunch these numbers. Weight for me is crucial. I resent those who call weight conscious people "gram weenies". Those are usually backyard campers anyway. I choose alcohol stoves due to their quietness. Except in a truly frigid weather spell or above treeline; both of those scenarios happen rarely to me nowadays.

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    1. You're very welcome. I certainly appreciate the ultra light, ultra reliable, and ultra quiet nature of alcohol stoves. It's very zen. Just sit back and be at peace.

      HJ

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