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Tuesday, December 30, 2014

Jetboils vs. Regular Stoves – Can a Jetboil Save Weight?

Seen recently on the internet:
"A Jetboil is so fuel efficient that you'll save weight."

That's an interesting statement.  I mean if we can save weight, wouldn't we want to?  Of course we would!  But is it true?  Let's do the math.  If you find math a little boring, don't worry.  The detailed calculations will be kept in the appendices.
The backcountry:  beautiful, but too heavy a pack can ruin your whole trip.  Will a Jetboil save you weight?
Fuel Weight Savings
First, since we're talking about fuel efficiency, how much fuel weight are we talking about here?  Well, you hear about Jetboils being able to do about nineteen or twenty boils of 500 ml of water per boil using a 100 g sized canister.  That works out to about 5 g of fuel used per boil, best case.  Obviously water temperature, air temperature, flame setting, wind velocity, elevation, etc. are going to affect that number, but for our comparison, let's go with 5 g per 500 ml boil.

My own experience with "regular" stoves tells me that it takes about 7 to 8 g to boil 500 ml of water.  Again that number will vary with conditions, but for our comparison, let's go with 8 g of fuel used per 500 ml boil.

If a Jetboil uses 5 g per 500 ml boil and a regular stove 8 g, then we save 3 g of fuel per boil.  Our actual savings will vary depending on conditions and the skill of the user, but let's go with a 3 g savings per 500 ml boil for our comparison.  Let's also assume that we boil water twice a day, once in the morning and once in the evening.  Obviously, in real life, some people will boil more or less water and will boil more or less frequently, but let's just use these numbers for comparative purposes and see what they tell us.
Upper Rae Lake, Sierra Nevada Mountains
So, let's plot a quick chart of what our fuel weight savings might be from using a Jetboil vs. a regular stove (full calculations are in the Appendices):
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Fuel Weight Savings (g) 6 12 18 24 30 36 92 98 104 110 66 72 78 84

Now, this is just fuel weight savings, not overall system weight savings, but those numbers look pretty good.  But what the heck happens on day 11?  How come our weight savings declines?  Well, at that point, we have to switch up to the next larger canister, a 230 g canister when using the Jetboil, a switch that occurred on day 7 with a regular stove.  This is important; more on this later.

Note that I'm using exact numbers for each 500 ml boil.  In real life of course, conditions vary.  Always plan with a margin for error.  In other words, bring a bit more fuel than you think you'll need in case conditions force you to burn more fuel than planned.  The numbers here are for comparison purposes only and should not be used for actual trip planning.
Longer trips are where more efficient stoves may save weight

Full "System to System" Comparison
The preceding section was just fuel weight.  To get a full comparison, we need to compare the total weight carried of a Jetboil vs. a regular stove.  The total weight would be calculated as follows:  Fuel weight + canister weight + burner weight + pot weight = total weight.  I won't include anything like canister stands or that sort of thing.

Now there are several problems here.  First, how do we get a weight for a "regular" type stove?  I mean some non-Jetboil stoves weigh 6+ ounces while some weigh less than 2.   We're going to have to make some kind of a decision here as to what burner or burners will be representative of "regular" (non Jetboil) burners.  Since our goal here is to save weight, it's reasonable to pick a relatively light weight burner.  Nowadays, the lightest burners from major stove companies are generally coming in around two ounces (57 g) or less.  I do computations in grams, so for ease of computation, let's assume our "representative" non-Jetboil burner is a nice even number, say, 60 g (2.1 oz).  Realize of course that there are lighter burners or heavier burners.  If you're looking at a particular burner, you can just substitute the weight of the particular burner you're interested in for my numbers here.

Various versions of the Jetboil
L to R:  Joule (2.5 L), Sumo (1.5 L), PCS (1.0 L), and Sol (0.8 L).
The second problem is which Jetboil to use?  I mean there is more than one model of Jetboil.  There's the original PCS, the GCS, the Flash, the Zip, the Sol (two different versions), the MiniMo etc.  Since we're talking about light weight, let's choose the lightest weight Jetboil ever produced, the titanium version of the Jetboil Sol.  If the Ti Sol can't save us weight, then no Jetboil can because all other Jetboils are heavier than a Ti Sol.

Third, what pot should we use?  Obviously the Jetboil Ti Sol comes with a 0.8 L pot, but regular stoves do not.  Since we're talking about weight here, I'm going to use a similarly sized "plain" (no heat exchanger) titanium pot, the Evernew 0.9 L ultralight pot.

Comparison 1 – Jetboil Ti Sol

So, with our comparison of the Jetboil Ti Sol to a regular stove set up, what have we got?  Let's do the math (full calculations in Appendix I).  If we use the fuel savings from above, we come up with the numbers in the third row of the below chart.  Some of those savings look pretty good.  For example, on a 10 day trip, we'd save 72 grams overall, about 2.5 oz.
Jetboil Ti Sol vs Regular
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Net Savings, partial cans (g) -32 -26 -20 -14 -8 -2 54 60 66 72 28 34 40 46
Net Savings, full cans (g) -122 -106 -90 -74 -58 -42 24 40 56 72 -92 -76 -60 -44
Net Savings, full cans (oz) -4.3 -3.7 -3.2 -2.6 -2.0 -1.5 0.8 1.4 2.0 2.5 -3.2 -2.7 -2.1 -1.6
Chart of weight savings.  Negative numbers indicate that a Jetboil is heavier.  Positive numbers indicate weight savings.

But are the weight savings real?  Well, possibly not.  You'd have to empty your canister before your trip to the exact amount of fuel you need.  What a hassle!  Oh, and did you let out too much gas?  Whoops, you just wasted a canister, and now you'll have to start over.

What in reality most people do is start with a full canister.  If you start with a full canister, the weight savings are shown by the fourth line.  There are still weight savings, but they don't start until about a week, and the weight savings are never more than about 75 g/2.5 ounces.  Seven to ten days appears to be the sweet spot where you'll save weight – with a Jetboil Ti Sol.  It matters very much which version of the Jetboil one uses as we shall see in our next comparison.

Comparison 2 – Jetboil MiniMo

OK, let's do another comparison, this time with Jetboil's latest, the MiniMo.  Everything is going to be pretty much the same in terms of the regular stove except that I'm going to use a bigger pot.  The MiniMo's pot is 1.0 L (the Sol's is 0.8 L), so in order to get a reasonable comparison, I need a pot that is about a liter in size.  In this case, I will use the 1.3 L Evernew Ultralight titanium pot.

Here are the numbers (full calculations in the appendices):
Jetboil MiniMo vs Regular
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Net Savings, partial cans (g) -174 -168 -162 -156 -150 -144 -88 -82 -76 -70 -114 -108 -102 -96
Net Savings, full cans (g) -264 -248 -232 -216 -200 -184 -118 -102 -86 -70 -234 -218 -202 -186
Net Savings, full cans (oz) -9.3 -8.7 -8.2 -7.6 -7.1 -6.5 -4.2 -3.6 -3.0 -2.5 -8.3 -7.7 -7.1 -6.6
Chart of weight savings.  Negative numbers indicate that a Jetboil is heavier.  Positive numbers indicate weight savings.

As in the previous example, the fourth line is going to give us the best estimates of weight savings, but in this case note that there are NO weight savings.  Using a MiniMo will always result in an overall weight penalty.  The weight savings due to fuel efficiency is insufficient to generate any overall weight savings.  The MiniMo is just too heavy.

Always carry the smallest practical canister size.  Larger canisters have more steel and more fuel and therefore more weight.

Concluding Remarks

Perhaps this is obvious from the above, but:
1.  The version of the Jetboil one uses matters.  Some Jetboils will save you weight overall in some circumstances.  Other Jetboils will not.
2.  The pot and stove one selects for one's regular stove matters.  I used ultralight titanium pots in my comparisons.  If you use heavier or lighter pots or stoves, you should substitute your weights for mine.
3.  Weight savings are achieved with a more efficient stove only when that efficiency allows you to avoid having to switch up to the next size larger canister (or worse carry two canisters).  Carrying the extra steel in the larger canister and the extra gas is a weight penalty you want to avoid.  An extra canister, even the smallest size, weighs about 7.4 oz/211 g.  That's nearly ½ pound.  In terms of saving weight, always avoid taking an extra canister or moving up to the next sized canister.
4.  It's worth noting that all of the weights I'm giving are the weight at the start of the trip.  As you burn fuel, your weight will decrease.  Ironically, fuel efficiency works against you here.  In other words, a stove that burns more fuel will result in a lighter load toward the end of a trip.  Of course, your pack is always heaviest on day one, so weight savings up front are the savings that matter most.
5.  Note that I've used Jetboil stoves in these comparisons.  However, these things apply to any integrated canister stove such as those from Primus or MSR.

I hope you find this post helpful.  As always, I thank you for joining me.

HJ

Appendix I  –  Jetboil Sol Ti vs Regular Stove Calculations

Jetboil Ti Sol Stove
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Grams per 500 ml boil 5 5 5 5 5 5 5 5 5 5 5 5 5 5
500 ml boils per day 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Total grams fuel needed  10 20 30 40 50 60 70 80 90 100 110 120 130 140
Canister weight (g) 100 100 100 100 100 100 100 100 100 100 150 150 150 150
Total fuel + can (g) 110 120 130 140 150 160 170 180 190 200 260 270 280 290
Regular Stove
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Grams per 500 ml boil 8 8 8 8 8 8 8 8 8 8 8 8 8 8
500 ml boils per day 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Total grams fuel needed  16 32 48 64 80 96 112 128 144 160 176 192 208 224
Canister weight 100 100 100 100 100 100 150 150 150 150 150 150 150 150
Total fuel + can  116 132 148 164 180 196 262 278 294 310 326 342 358 374
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Fuel Weight Savings (g) 6 12 18 24 30 36 92 98 104 110 66 72 78 84
Jetboil Sol Burner (g) 102 102 102 102 102 102 102 102 102 102 102 102 102 102
Regular Burner (g) 60 60 60 60 60 60 60 60 60 60 60 60 60 60
Burner Weight Penalty (g) 42 42 42 42 42 42 42 42 42 42 42 42 42 42
Jetboil Ti Sol Pot (g) 106 106 106 106 106 106 106 106 106 106 106 106 106 106
Evernew Ultralight 0.9 L (g) 110 110 110 110 110 110 110 110 110 110 110 110 110 110
Pot Weight Savings (g) 4 4 4 4 4 4 4 4 4 4 4 4 4 4
Jetboil Ti Sol vs Regular
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Net Savings, partial cans (g) -32 -26 -20 -14 -8 -2 54 60 66 72 28 34 40 46
Net Savings, full cans (g) -122 -106 -90 -74 -58 -42 24 40 56 72 -92 -76 -60 -44
Net Savings, full cans (oz) -4.3 -3.7 -3.2 -2.6 -2.0 -1.5 0.8 1.4 2.0 2.5 -3.2 -2.7 -2.1 -1.6
Full canister fuel weight (g) 100 100 100 100 100 100 100 100 100 100 230 230 230 230
Excess fuel carried (g) 90 80 70 60 50 40 30 20 10 0 120 110 100 90

Jetboil Ti Sol (left), Jetboil MiniMo (right)

Appendix II  –  Jetboil MiniMo vs Regular Stove Calculations

Jetboil MiniMo Stove
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Grams per 500 ml boil 5 5 5 5 5 5 5 5 5 5 5 5 5 5
500 ml boils per day 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Total grams fuel needed  10 20 30 40 50 60 70 80 90 100 110 120 130 140
Canister weight (g) 100 100 100 100 100 100 100 100 100 100 150 150 150 150
Total fuel + can (g) 110 120 130 140 150 160 170 180 190 200 260 270 280 290
Regular Stove
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Grams per 500 ml boil 8 8 8 8 8 8 8 8 8 8 8 8 8 8
500 ml boils per day 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Total grams fuel needed  16 32 48 64 80 96 112 128 144 160 176 192 208 224
Canister weight (g) 100 100 100 100 100 100 150 150 150 150 150 150 150 150
Total fuel + can (g) 116 132 148 164 180 196 262 278 294 310 326 342 358 374
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Fuel Weight Savings (g) 6 12 18 24 30 36 92 98 104 110 66 72 78 84
Jetboil MiniMo Burner (g) 130 130 130 130 130 130 130 130 130 130 130 130 130 130
Regular Burner (g) 60 60 60 60 60 60 60 60 60 60 60 60 60 60
Burner Weight Penalty (g) 70 70 70 70 70 70 70 70 70 70 70 70 70 70
Jetboil MiniMo Pot (g) 240 240 240 240 240 240 240 240 240 240 240 240 240 240
Evernew Ultralight 1.3 L (g) 130 130 130 130 130 130 130 130 130 130 130 130 130 130
Pot Weight Savings (g) -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110 -110
Jetboil MiniMo vs Regular
Trip Length (Days) 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Net Savings, partial cans (g) -174 -168 -162 -156 -150 -144 -88 -82 -76 -70 -114 -108 -102 -96
Net Savings, full cans (g) -264 -248 -232 -216 -200 -184 -118 -102 -86 -70 -234 -218 -202 -186
Net Savings, full cans (oz) -9.3 -8.7 -8.2 -7.6 -7.1 -6.5 -4.2 -3.6 -3.0 -2.5 -8.3 -7.7 -7.1 -6.6
Full canister fuel weight (g) 100 100 100 100 100 100 100 100 100 100 230 230 230 230
Excess fuel carried (g) 90 80 70 60 50 40 30 20 10 0 120 110 100 90