Tuesday, September 9, 2014

How Much Canister Gas Do I Need?

Sometimes I see people bringing a lot more gas for their canister stove than they really need.  Now, it never hurts to be prepared, but really? A 450g canister for a simple weekend trip?  That's potentially a lot of extra weight to pack up a mountain.  Of course we don't want to run out of gas, but let's see if we can't do a little bit better in terms of coming up with an estimate of the gas we might need.
The three standard threaded backpacking canister sizes:
(L to R) 450g, 220g, and 110g.  Note:  Some brands vary as to exact amount of gas.

Now, before I give you my estimates, let me say that my estimates are based on my experience and my style of stove use.  You are your own best estimator.  If you're somewhat new to backpacking, then I'd say err on the side of caution and assume that you'll be doing "complex" cooking and select fuel based on that column from the table below.

What about White Gas?
What's that you say?  You don't use canister gas; you use white gas?  Ah.  No worries.  Check out How Much White Gas Do I Need?

Making Your Own Estimates
As for your own estimate based on your cooking style/stove use style, first you need to get a gram scale. Then weigh your gas canister before your trip.  On every trip, keep track of how many meals you cooked and what type of cooking was involved.  After your trip, weigh the canister again.  The difference between the starting weight and the ending weight is the amount of gas you used.  If you've kept track of how much and what type of cooking you've done, you should be able to start estimating your gas usage after a few trips.

Estimates in the Field
You can also make a rough estimate of how much fuel you're using while you're out on a trip.  See my article in Seattle Backpacker's Magazine, How Much Gas Do I Have Left?

Using Less Fuel 
Whatever you do with a stove, keep efficiency in mind.  There are basic things you can do to use less fuel while you're cooking.  I commend to you my earlier blog post, Canister Gas Stoves -- Recommendations and Efficiency.

My Estimates 
OK, now here are my estimates.  Note that when I boil water, the water is normally around 40F/5C to 50F/10C in temperature.  Significantly warmer or colder water may cause you to use more or less gas.  If you're melting snow, you should roughly double the below estimates.

For a solo trip
Jetboil Conventional Canister Gas Stove
(simple cooking)
Conventional Canister Gas Stove
(more complex cooking)
Grams per day 15 20 30
For two
Grams per day 23 30 45

Now, notice two things:
1.  For a simple weekend trip, for one person, there's no need to ever bring a 450g canister.  A 110g canister should do nicely unless you're doing a lot of extra heating for drinks, dish water, bath water, etc.   A reasonably conservative person shouldn't need more than one small canister of gas for a weekend.
2.  I do not double my estimates if a second person comes.  It's usually more efficient to boil more water at a time.  In other words, if you're going to boil a liter of water, do it all at once.  Don't boil 500 ml, empty the pot, and then boil the second 500 ml.  I'm assuming here that you brought a pot large enough for two people.  If not, then you may need to allow for higher gas usage.

Remember that my estimates are just that, estimates.  Always check that your experience is similar to mine before relying too heavily on my estimates.  Particularly in very cold or very windy conditions, gas usage may increase significantly.

I hope you find this post helpful,


Notes and Assumptions
1.  The figures above assume about 6 cups (approx. 1.5L) boiled per day for simple cooking.
2.  Water temperature is assumed to be around 40F/5C to 50F/10C.
3.  The figures in the table above do not include snow melting.
4.  The figures above assume you know how to operate a gas stove reasonably efficiently (turn it down!  Running on high wastes gas.) and that you've taken measures to shield the stove from wind.
5.  The figures above also assume that you have a pot that is wide enough to catch the flame.  Users of tall, skinny pots with a conventional gas stove will generally use more gas.
6.  Air pressure is assumed to be approx. 900 mBar, the air pressure normally found at about 3000'/900m in elevation.  Stove use at lower elevations may require more gas.  Stove use at higher elevations may require less gas.

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