I've visited this question before, but now that super ultralight (SUL) canister gas stoves are available, it's time to re-visit the subject.
|The BRS-3000T, the world's first super ultralight (SUL) canister gas stove – a mere 25 grams!|
What do I mean by "SUL?" How do we classify canister stoves? Well, here's my schema:
Canister Gas Stove Weight Classes
(Less Than or Equal To)
|Super Ultralight (SUL)||1||28|
Basically, if a canister stove weighs less than an ounce (28 g), that's SUL in my book. If a stove weighs more than a quarter pound (113 g), that's heavy. I think that's a fair and reasonable categorization, given the state of the art.
But, Hikin' Jim, uh, isn't this post about comparing gas to alcohol? All you've done so far is talk about gas.
Ah, yes, quite right. So, for a given trip, which is lighter, alcohol or canister gas? Let's do some math. If you don't like math, then by all means skip down to the discussion, but in order to really feel like I'm on solid footing here, I need to go through the details.
First, for the purposes of this discussion, I'm going to assume that our gas stove and our alcohol stove set ups weigh about the same. In the case of the BRS-3000T, that would be 25 grams.
Second, I'm allocating 30 g for the alcohol container and 100 g for the gas canister. Those may not be representative of all containers and canisters everywhere, but let's just go with it for now.
For this example, assume the individual is going to boil 500 ml of water twice a day. Based on that assumption, I allot 40 ml of alcohol or 20 grams of gas per day. Both of those could be overstated, but these are round numbers for comparative purposes.
The specific gravity of alcohol is about 0.8, so our 40 ml/day of alcohol is going to weigh about 32 g/day.
I've laid out an example in the below chart, based on a 5 day trip. By the way, this spreadsheet is available for download if you want to run your own numbers. See the "Get your own danged spreadsheet" section of this post.
|Alcohol Calcs||Alcohol Set Up (grams)||Gas Set Up (grams)||Alcohol Set Up (ounces)||Gas Set Up (ounces)||Gas Calcs|
|Fuel/Day (ml)||40||20||Gas grams/day|
|Days on Trail||5||0.0||0.0||100||Total Gas Weight (g)|
Now, the "conventional wisdom" is that a trip shorter than X days is going to be lighter with alcohol but that all trips longer than X days are going to be lighter with gas, the presumption being that since gas is more calorically dense, one would eventually overcome the heavier weight of the steel canister in which the gas is housed. There's some disagreement on exactly what "X" is, but this is the basic argument, that a trip longer than X days will be lighter with gas.
But is it really true? Well, take a look at the bottom line, total weight, in the chart above. For a trip of 5 days, alcohol is just slightly lighter, by 20 g, than gas. Ah! There you go. So, for anything beyond that, gas will be lighter, right?
Well, maybe not. Look at the far right column. Do you see the cell labeled "Total Gas Weight"? Look at that number there, 100 grams. So, let's see, one more day than five would be six days, and on the sixth day, we'd add another 20 grams, our daily allotment, giving us a total of 120 grams of gas... But our canister only holds 110 grams of gas. Oops.
Therein lies the problem with the "conventional wisdom". Canister gas is only sold in lots of roughly 4, 8, or 16 ounces (about 110g, 220g, or 450g; brands vary). The problem with the "conventional wisdom" is that on day six you have to size up to the next larger canister, and... alcohol becomes lighter again.
Now, are my numbers for every person for every trip? Probably not, but in general the rule should hold: Gas will be lighter after a certain number of days – until you have to size up to the next larger canister.
Here's how it maps out, in the chart below. Negative numbers in the difference column mean that gas is heavier. Positive numbers mean that gas is lighter.
Empty canister weights are as follows:
110 g size = 100 g empty
220 g size = 150 g empty
450 g size = 210 g empty
|Days||Alcohol Set Up (grams)||Gas Set Up (grams)||Difference (grams)||Alcohol Set Up (ounces)||Gas Set Up (ounces)||Difference (ounces)|
Notes on the above chart:
- For days one through four, alcohol is about 5 to about 2 ounces lighter.
- On day five, it's less than a one ounce difference between the two, but alcohol is still a bit lighter.
- But on day six, the amount of weight saved by using alcohol increases to 1.3 oz. Why? Because we had to size up to the next larger canister.
- By day seven, you're at basically a break even.
- For days eight through ten, finally gas is actually lighter.
- On day eleven, alcohol goes back to being the lighter weight option again. Why? Because we had to size up to the next larger canister.
- Finally, starting on day twelve, gas is always lighter, increasingly so, for the remainder of the three week period that is mapped out in the above chart.
- Trips of one to four days have reasonably good weight savings when using alcohol.
- Trips of five to eight days don't show a whole lot of difference either way.
- Trips longer than eight days will generally see better results with canister gas, with the exception of day eleven where alcohol will be lighter.
Get Your Own Danged Spreadsheet!
Don't like my numbers? That's perfectly understandable. Use your own numbers. You can download my Excel spreadsheet, which is in xlsx format, and then you can run any number of different scenarios. Cells in which you need to enter values into are highlighted in yellow. You need to enter the following:
- Stove weight, once for alcohol and once for gas.
- Container weight, just for alcohol. Gas container weight will be calculated for you based on how much total gas your trip requires.
- Fuel per day, once for alcohol and once for gas.
- Days on trail.
Once you enter the above values, the spreadsheet will calculate the total weight for both alcohol and gas. The results will be displayed in both metric (to the left) and English (to the right) units. I hope it's helpful to you.
Does It Matter?
However, considering how excited people get over a stove that weighs about an ounce and a half (FMS-300T) vs. a stove that weighs about one ounce (BRS-3000T), I'm thinking that there are people that will be interested. Regardless, the spreadsheet is here if you want to use it. Whether or not it matters, well, that's up to you.
Tailoring to the Trip
Let me leave you with one last thought: Sometimes starting pack weight isn't the only issue.
What do I mean by that? Well, recall that you have to burn more alcohol per day to boil the same amount of water. Your pack weight will fall faster with alcohol. With gas, your pack weight decreases more slowly, and you've always got at least a quarter pound lump of steel in the bottom of your pack – the canister.
If you're planning a trip where you've got a big first day, then of course you want to minimize your first day's weight. But if you're planning a trip where there's a rough go in the middle or end of the trip, you might actually want to choose alcohol since your pack may be lighter – at the time that you do the rough section – despite having a higher initial starting weight. If you're going to have big climb, a tricky scramble, or a XC route toward the end of the trip, it might make sense to bring alcohol even if it were heavier at the start of the trip.
Thanks for putting up with all the math,