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.