Most fuel-efficient on Snow Peak Litemax (or other canister stoves)

I have the Kovea branded version of that stove.
When I used that , a few years ago, I did perform some tests and concluded that it was most efficient ,for a boil, at around half throttle.
That was using Ti pots around around the 900ml/ 1 liter size, about 5" wide.
my take is that with a bigger flame a lot of the heat was just going up the side therefore almost wasted.
In practice I try to keep the flame of my gas stoves at around 1/3rd less than the pot diameter.
But yes that is not very scientific, it just happens to work for me.
Franco

Misha,
Yeah, Basically you are doing what I tried 20 years ago. You bump into all sorts of variables. Wind, air temp, thickness of pots, distribution of heat, etc…

To call all this stuff meaningless is not worthy of my scientific training, but basically, ignoring heat loss and assuming a good wind screen/heat trap, you'll find that the lowest heat you can still manage to burn consistently on a stove, the more efficient it is. Nearly linear between 3 and 14 minutes, anyway. In a lab, boiling to 200F on a digital thermometer, I get good efficiency at about 13-15 minutes for two cups (16oz) of water using a small alcohol based stove: roughly 1/3oz of 50/50 ethanol/methanol from 40F, to 200F. (Note that 200F was chosen to avoid the effects of altitude and day to day air pressure changes.) Efficiency goes down about .05oz per minute for each minute I boil faster. The best time vs fuel was about 5:30 and 5/8oz of alcohol. An even slower boil runs into things like radiative cooling and convectional loss over the lid. So it starts leveling out…bumping in to that "too slow" region that makes no sense out camping.

Since no canister burns that slowly, I can only conclude that the lowest possble flame on a canister stove (or WG or Kerosene stove) will be the most efficient. Indeed I tried it with two canisters I had (picked up at the same time and from the same place) and I got 5-6 extra boils out of the canister on "as low as it would go" as opposed to the canister on 3/4 throttle. This wasn't very scientific, though. I just kept cycling between emptying the pan and pouring a premeasured amount in as it alarmed, filling the premeasure, again. Took a couple hours.

A heat exchanger on the bottom of the pot will help as much as 15%. I think this pot is one that will work on any stove: Olicamp XTS Pot (1L size) A side screen will add another 5-8%, minimum. I think the adds say 40%, well…maybe for a half or quarter cup at a time.

Fascinating! I will definitely test this for myself when I get the chance. This outcome strikes me as quite elegant, as it is largely independent of (mild) temperature and pressure variation because as you said you can't turn the flame down low enough for the heat loss from the top and sides to outweigh the benefits of the low flame anyway.

Do you think the reason for this trend is simply the efficiency of the burn, or just the flames whisking around the edges of the pot? In other words, should I be worried about greater exposure to CO while waiting for my water to boil on low heat? We did assume no wind ;)

It would be interesting to repeat the test with a catering tray for a pot, which would be similarly thin, and the bottom would approximate an infinite plane and therefore eliminate fringe effects.

Misha: I'm a UCB BS ChemE living 2100 miles to your NW.

Short version for a cannister stove:

Paint the bottom of your pot. Surprisingly, white, black and red paint are all black in the infrared (as determined side-by-side on identical stoves in my well-equipped garage).

Wider pots are more efficient than tall pots.

Moderate flame setting. I want to say a little higher in cold weather, a little lower in warm temps, but I haven't confirmed it experimentally.

A good cover cuts evaporative losses.

A modern HX pot comes out ahead after 5-10 liters of boiled water. i.e. not needed for a weekend trip, but desireable beyond that. Definitely for any snow camping where you are melting snow for drinking water.

A modern HX pot also can extract enough heat to allow an insulating "coozy" around the sides of the pot which obvious reduces heat losses, but I'd only do that if I was simmering for a long time*

Most all the resistance to heat exchange is in the air film on the outside of the pot. Vortex generators akin to those on airplane wings help at almost no weight (checked that myself)

Windscreens help all the time. A huge amount in the huge.

*This is a bigger tip than all the heat exchange mumbo jumbo: Don't think of COOKING your food (time and temperature), think of it as REHYDRATING it. Soaking in cold water cuts cooking time of noodles, ramen, beans, rice. Letting stand once boiled allows you to stop the burner much sooner. (You really don't want to eat 100C food anyway!). Experiment at home, but most foods can be perfectly cooked only by bringing close to a boil once (at most, one more time 5-10 minutes later). Never simmering (by selecting WHAT you cook and changing HOW you cook it) saves a LOT of fuel.

"Do you think the reason for this trend is simply the efficiency of the burn, or just the flames whisking around the edges of the pot? In other words, should I be worried about greater exposure to CO while waiting for my water to boil on low heat? We did assume no wind ;)"

The efficiency of the burn has little to do with it at low settings. Generally, the low settings would require a reduced air inlet at the jet. . .like a Bunsen burner. This would provide the optimal mix of cooler air into the gas hence burning. Since all backpacking stoves have a fixed orifice, usually set to high flow rates, we get too much air in the flame anyway. This means more oxygen than is really needed at low settings. This leads to high efficiency burning for all but overloaded settings. It *is* possible to overdrive a canister and reduce heat production, increasing CO production. But, generally, you do not need to worry at low settings. CO2 is a worry in a confined area. Reburning that will also produce CO. You always get some, anyway. Generally, you will get slightly less CO with plenty of air, but a cooler flame. One of those things that I was explaining about in the plethoria of minor variables. There is a curve to CO production, related to the air input and the actual gas/air mix you are burning. But, I do not worry about it. If I were to use it for 3-4 days in a tent, I *might* detect a slight increase in CO in your blood, but certainly not enough to make you sick. It dispurses slowly, however. For a week, I would use more caution since even small amounts can build up in your blood stream.

I used the alcohol blend because it approximated the SLX I normally use for camping. It burns pretty clean, depending on the size of the vapour outlet. However, the additional air will likely cool the flame somewhat. It doesn't really matter because the heat still needs to extracted from the flame/hot air rising from around the flame. Any air warmed by the flame carries heat to be extracted from the system, so it doesn't really matter. I am not looking to adjust flame temp, I am adjusting the entire heat producing system. Most of that stuff evens out with alcohol, WG, Kerosene, and canisters, too, provided you have enough oxygen for burning them.

Turbulence, vortex generators, heat exchangers (HX's,) nsulated sides are all cheats to get to the infinite plane you are talking about in a finite, small area.

David is quite correct. Painting the fins with a IR absorber will help. As will induced turbulence (through vortex generators) and insulated sides and lid. I disagree that medium temp is the best for raw efficiency, however. It may be the best for time vs efficiency…never checked that with canisters except roughly. The most fuel efficient, ignoring time to boil, is low in a good system.

I disagree that medium temp is the best for raw efficiency

Yes me too…
I should have clarified what I meant by "efficient" .
My aim is a balance between low usage and burn time, that is why I like the Caldera Cone 550ml kit.
It isn't the fastest nor the most miserly in fuel used but gives me a great balance between the two.
With alcohol I can make a Tea Light burner that boils 500 ml with less fuel than the CC however it takes twice as long (15 min and more for two or three g less) .
So I suppose that in moderate temps it works like that with canister stoves too, however saving maybe one or two grams and doubling the boil time does not work for me.
Around freezing and below I suspect that with most stoves a low setting will never (….) give you a boil.
Franco

While comparing my Gigapower to my, at the time, newly acquired Litemax I never found that a lower setting produced very efficient results. More surprising, I found that 8oz cans (what I was using) taper off quite a bit as they get lower and lower. There are a LOT of variables that effect a stoves efficiency. Can level, can temp, wind, air temp, water temp, covered or not, pot material, pot width, flame pattern. You could drive yourself crazy trying to produce results that will simulate your real experience.

My suggestion? Use the stove and find out if you like it. My results of Gigapower vs. Litemax proved that I could maybe get one extra boil out out of an 8oz can…and a lot of personal time.

True, some stoves are drastically different in performance. I kinda just see canister stoves two ways…they either stink or work good…and they're either heavy, medium or lite. ;) IMHO

Franco, yeah, at about a 15minute boil it gets slow enough that beloow 32F (0c) it may never boil (it actually does boil, BTW at about 20 minutes, but any wind will kill it.)

8oz cans are simply not wide enough to get good boil times. They are the oposite of what makes a pot a fair to good water boiling pot…tall and narrow. You want short and wide. The CC is great for alcohol. But modifying a cone by opening around the canister works real good. 6-8 VERY LARGE holes, opening the entire canister portion to cooling air, works real well. As Rand says, DO NOT TURN THE GAS ON before lighting the stove…want to guess what happens? You do need to support about 1/2" above the flame for optimum results. CC does not make one for canisters. Make your own. They work second to none, but *monitor* heat feedback into the actual canister of gas. If you cannot hold your finger on it, it is too hot. On low, this is rarely a problem. Note that this trick works for cold weather, too. Be carefull about heat feedback into the cannister! Coupled with a heat exchanger pot, this is better than the JetBoils, though. Again, always on low.

James — can you clarify two points? Slightly confused.

First, isn't it necessary to turn on the gas before lighting it? I suppose you could eliminate this "dead time" by using a lighter and turning it on in advance, but in my experience even taking several seconds to get good sparks from a magnesium rod doesn't let anything get out of control.

Second, what do you mean "You do need to support about 1/2" above the flame for optimum results?" 1/2in of what, the windscreen? In other words, is the idea to prop up the windscreen so the bottom is 1/2" above the flame source? How are you supposed to keep it levitated there? Are the CC modifications to allow it to stand on the ground while providing sufficient air flow to keep the canister cool?

Lastly, I know this is strictly against the instructions — but wouldn't allowing the canister to heat up when it's nearing empty (say, by lowering the wind screen) allow you to squeeze more fuel out of the canister? It shouldn't be dangerous since you're just making up for lost pressure. Perhaps "not too hot to touch" is a good guideline for heating it up? I have an MSR Titan 850mL, and a 6in aluminum screen on its way from AGG.

Thanks for all the input!

James M,

I am pretty sure he ment 8oz cannisters not an 8 fl oz cook pot :) I think Ken might be defining effeciency as time to boil and describing the phenom of a canister being more prone to internal pressure issues when low on fuel mass and cold enough outside.

David, I would love to see some pics of your vortex generator.

Yeah, my writing is poor at best. Sorry!

The main objection I got from Rand was that you could end up with gas and air mixed in the cone. Add a spark and poof.

The cone used for canisters should support the pot about a 1/2 above normal, ie the normal pot stand. The holes shold be no higher than the adjustment level. This is due to trapping cumbustion inside the cone to transfer the heat to the water. You also use the sides of the pot to do the transfer, increasing the surface area exposed to the heat. At least this is what I got experimentally, I never really figured out why. I just do it. Theoretically, you light the stove and place the screen/filled pot over it. it should just clear the valve adjuster. Note that you may need to shorten the adjuster, though.

Yeah, feedback can get good or bad. It depends on the outside temp. But like I say, monitor it with a finger every couple minutes. If it seems hot, turn it off or down. Avoid bursting!!! You also need extra holes in the top for exhaust with a canister.
All together, it works very well.