QuietStove.com

Tuesday, April 18, 2017

How Much Gas Do I Need for My Jetboil? (or other high efficiency stove)

Here's a perennial question:  How much gas do I need for my Jetboil?  And, really, this would apply to not only Jetboils but to any high efficiency stove set up.
A one liter pot from Primus.
Note the heat exchanger at the bottom of the pot.
Generally, a "high efficiency stove set up" means an integrated canister stove (Jetboil, Reactor, Windburner, Eta Express, etc), but there's no reason that you can't go out and just get a heat exchanger pot and create your own high efficiency stove set up.  Combine your existing stove with a heat exchanger pot, turn it down to a moderate flame, and you've got your own high efficiency stove set up.

What's out there in terms of ready made high efficiency stove systems?  You might want to take a look at my article Integrated Canister Stoves – The State of the Art.

But back to the original question:  How much gas do I need for my Jetboil (or other high efficiency stove set up)?

Background
The "de facto" standard for simple backpacking cooking is the "two cup boil" (about 500 ml).  Why?  Because that's what most freeze dried backpacking type meals require.  Things like ramen also require about 2 cups of water as do other popular backpacking meals like Knorr's rice or pasta.  Of course some meals require more and others less, but 2 cups/500 ml is a pretty good starting place.

But of course, some people will have hot meals once per day, some twice, and still others three times per day.  So, it's not just "two cups" that we've got to worry about but also how often we boil up our two cups.  And of course, there are those who want a hot cup of coffee, cocoa, or tea with their meals.

Let's look at three scenarios and see what we come up with.  I'm going to arbitrarily set up these numbers for a five day trip, just as an example.  You'll need to adjust these numbers if your trip is either shorter or longer.

First, I'll briefly describe each scenario, and then I'll have a chart "doing the math" and comparing the three scenarios.  There will be a discussion section after the numbers and charts.

Scenario 1 ("Minimal")
In Scenario One, I'm going to describe somewhat "minimal" use.  Our backpacker here will not have hot food every meal but rather will have only hot food twice a day.  So, somewhat minimal but hardly extreme.  Now, this is a five day trip, but I'm going to assume that our backpacker will eat breakfast before he or she hits the trail on day one and that he or she will leave the trail after supper on the last day.  This is usually the way I set up my trips, so I think this is a reasonable assumption.  Therefore our backpacker will have four breakfasts and four suppers.  Our backpacker boils 2 cups/500 ml for each hot meal.  If you run your trips differently, adjust these numbers accordingly.

Scenario 2 ("Moderate")
In Scenario Two, I'll describe what I call "moderate" use.  Our backpacker in Scenario Two will eat three hot meals per day.  All else remains the same.

Scenario 3 ("Heavier")
In Scenario Three, I'll describe what I call "heavier" use.  Our backpacker in Scenario Three will eat three hot meals per day and will have one cup of hot beverage per meal.  All else remains the same.

OK, so let's lay this out in a series of comparative charts.


Discussion
With a high efficiency stove set up, it's perfectly reasonably to boil two cups (500 ml) of water with 5 g of fuel.  Of course you'll want to know the Rules of Stove Fuel Economy so that you don't wind up blowing your grams per boil.

With "minimal" use, we use only 40 grams of fuel for a 5 day trip.  That's pretty good! Since most small ("four ounce") size fuel canisters contain 110 grams of gas, we're totally covered with one canister.  Nice.

With "moderate" use, we're at 68 grams for a 5 day trip.  Note that I used "4.5" as the number of days.  I'm still assuming our backpacker will eat breakfast before starting and eat supper after ending, but recall that in Scenario Two (moderate), our backpacker has a hot lunch every day, so I add in an extra half day to account for the extra meal.  I guess strictly speaking it should be a third of a day, but close enough.  Again, we're well within the capacity of a single 110 g canister of gas.

Even with "heavier" use, were still only at 101 g of fuel used.  Yes, that might be cutting it a little close to bring a single 110 g canister of gas when you plan to use 101 g total. but if you ran low, you could forego you hot beverage at lunch on the last day.

Now, these are fairly rigid scenarios.  Every meal is the same.  But even if you flex things around a bit, so long as you're not boiling more than nine cups/2.1 liters per day (and only six cups/1.4 liters on the first and last day), you're going to be OK with just one small size canister.  That's pretty nice.  That's the advantage of a high efficiency stove set up.   When you can avoid sizing up to the next larger canister (or carrying multiple canisters), a high efficiency stove set up will likely save you weight overall.

Compatible Canisters 
"But Jim!  I have a Jetboil.  Jetboil only sells 100 g canisters of gas.  If I use a non-Jetboil canister the sky will collapse, I'll get a hair lip, and my dog will wet the rug."

Uh, no.  You can pretty much use any brand of canister with any brand of stove.  Pretty much (there are exceptions).  You might want to check out my article Can I Use Any Brand of Gas Canister?

Why anyone would buy Jetboil brand small canisters when you can get more gas for the same price by buying another brand is beyond me.  Yes, it's "only" a 10 g difference, but recall that a two cup boil requires only 5 g of gas with a high efficiency stove set up.  You're giving up two meals every time you buy Jetboil brand small canisters.  No, thanks.

Cautions 
You should always use your own habits to estimate your fuel usage.  Don't just rely on my scenarios.   These scenarios are meant to stimulate your thinking not dictate your fuel usage.

If you're new to this, you might want to be a bit more conservative in terms of your allotment of fuel than what I've outlined above.

If you're melting snow to get water, double all of the above estimates.


I hope you found this post useful.  Thanks for joining me,

HJ

Appendix
Some people, depending on what type of device they are using, may find it easier to read the chart in HTML format.  Here is the chart in HTML format:
Minimal    Moderate    Heavier
H2O (ml) gas (g) H2O (ml) gas (g) H2O (ml) gas (g)
Breakfast 500 5 Breakfast 500 5 Breakfast 750 7.5
Lunch 0 0 Lunch 500 5 Lunch 750 7.5
Dinner 500 5 Dinner 500 5 Dinner 750 7.5
Per Day 10 Per Day 15 Per Day 22.5
Days 4 Days 4.5 Days 4.5
Total 40 Total 68 Total 101

1 comment:

  1. i found this very helpful and VERY clearly written, but i also wonder how you figure in number of people. That is, are these numbers for 1 person, therefore I need to double the numbers if we prepare 2 backpack meals? Is there any economy in cooking up two meals one right after the other? thanks!

    ReplyDelete