QuietStove.com

Monday, August 29, 2011

Fastest Boil Time?

So, which stove has the fastest boil time? Or does it even matter?

If you read my reviews, you'll notice that I don't normally list boil times. Why do you suppose that might be?

First, how important is it? Something in the neighborhood of 5 to 7 minutes to boil a liter is fine in my book. Waiting another 30 seconds or so for a boil makes no real difference to me. Now, if it were another 3 minutes, maybe then I'd worry about it, but half a minute either way isn't going to really affect how I cook or how I organize my time while backpacking. After all, isn't one of the reasons we go backpacking to get away from all of the arbitrary time pressures of "civilization?"

Second, don't forget the number one rule of stove fuel economy:
1. Turn it down! High heat = inefficient = wasted fuel.
2. Use a lid. Escaping steam = escaping heat = wasted fuel.
3. Use a windscreen. No windscreen = dispersed heat = wasted fuel.

Running a stove on high burns through more fuel than you really need; you can accomplish the same with less fuel if you just run it on a low to moderate flame. You are carrying that fuel on your aching back, aren't you? Shoot! Conserve it. Why worry about shaving 30 seconds off a boil when the price is to carry more fuel?

Third, how helpful is a boil time in comparing one stove to another? There are no standards for boil times. If there were a standard (e.g. 1 liter of water at 45F/7C, 5mph/8kph wind, plain aluminum pot with lid, 1 atmosphere pressure), then we could compare boil times stove to stove and perhaps have something meaningful. But there is no standard, so one stove company may be boiling water that is 45F/7C outdoors whereas another company may be boiling water that is 75F/24C in a windless laboratory. That's like comparing a diesel truck to a skateboard. One stove manufacturer may have its facility in Denver, Colorado (elevation about 5000'/1500m) whereas another may have its facility in Chicago, Illinois (elevation about 600'/180m). Comparison of boil times from those two locations isn't even close to relevant.

So, to my point of view, a boil time doesn't figure prominently as I evaluate a stove. Sure, it has to be within reason, but even 60 seconds either way wouldn't have any significant effect on my enjoyment of the outdoors. Not only that, if I start focusing on maximizing my boil times, I'm just burning through fuel -- fuel that I have to pack. And finally, since there is no set of standard conditions for boil times, they're of little use for comparing one stove to another. Don't forget that boil times vary even on the same stove. If one boil takes 4:45, 5:15 the next, 4:35 the next time, and then 5:05 on the boil after that, a stove company will probably pick the single fastest time and list that as their official boil time. Singularly useless.

To me at least, boil times are just the "macho" claims of stove advertisers. Within reason, boil times aren't really important to a guy sitting by a beautiful alpine lake trying to get away for a while. So, don't sweat the boil time. Look at how you cook, what you cook, and under what conditions you cook. How a stove serves you in the context of how you do things in the outdoors is going to matter a whole lot more than 30 seconds off your boil time.

HJ

3 comments:

  1. I look at BTU output or watts. But I don't think that high heat = ineffecient. In fact, it seems quite the opposite.

    Here's a link I found interesting:
    http://ujdigispace.uj.ac.za:8080/dspace/handle/10210/2560

    The authors tested a variety of stoves, primarily interested in wick-fed stoves, but used a Nova+, Omnifuel, and Dragonfly to compare.

    I am not able to open the PDFs at this moment but please correct me if I am wrong -- if I recall, the efficency of the stove decreased as power output decreased, and stoves were most efficient at full output.

    What I have noticed is that with roarer type burners, as you turn down power output you start to notice a rather awful fuel smell. Unburned but vaporized fuel. I theorize that this is due to less heat reaching the generator resulting in decreased gassification of the fuel or just because the fuel / air mix becomes more turbulent and less stable making pockets where it is too lean or too rich to properly combust because the flame cannot propogate as well.

    There is obviously some other considerations. If you crank up the burner to create a flame bigger than the pot bottom, you have big spill and heat escaping up the side of the pot wasted. Plus there seems to be a limit of how fast a pot can absorb heat. If something is already boiling, it cannot get any hotter so any more heat is wasted.

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  2. Hi, Anthony. I haven't had a chance to read that article, but I will hopefully tomorrow.

    As for efficiency, stoves tend to run more efficiently at lower output than high. In every test I've ever run, running a stove on high used more fuel to achieve a certain outcome than on a low or moderate flame.

    On the other hand, I don't think you can increase efficiency indefinitely by simply continuing to lower the flame. There is some optimum setting out there, somewhere in the lower range of a stove's operating output.

    My results are pretty consistent with what I've read from others. If you want fast, you'll get less efficient AS A GENERAL RULE. Of course some fast stoves are more efficent than others and simply being slow doesn't automatically imply efficient. Generally though, there is a trade off: faster burns more fuel (i.e. less efficient) and slower burns less fuel (i.e. more efficient).

    HJ

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  3. Hi, Anthony,

    Very interesting study. Thanks for forwarding that to me.

    I didn't see any comments regarding flame size and efficiency. Was there a particular section you had in mind?

    HJ

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