Safety of heat exchangers on cannister stoves.

[Shawn Basil]

I have a question for those who have used heat exchangers on cannister stoves during cold weather. I have no experience with them, but the technique sounds like it should post a major explosion risk. A passage from Climbing Magazine says this:

"A heat exchanger — a piece of copper tubing that wraps around your canister, with one end passing through the flame — helps your stove operate efficiently in cold weather (or when your canister is running low) by heating up the canister and thus pressurizing its contents. Heat exchangers enable your stove to spit out more fuel, and therefore more BTUs. In a cold environment, a heat exchanger can be essential; without one, butane stoves have a tendency to sputter as the fuel runs low. After coiling the heat exchanger around a new canister, I wrap the canister in aluminum foil and then slip the whole fuel assembly into a custom-made, duct tape-covered foam cozie. This insulates the heat exchanger (making it more efficient), and prevents it from melting gear, should you inadvertently bump the stove while cooking."

Considering that Snow Peak specifies to avoid exposing their cannisters to temps above 120 degrees F, how can it be safe to use the system if the cozy is necessary to prevent the exchanger from "melting gear"?

Am I missing something or is this a really bad idea?

Also, the poster claimed to have used this system hundreds of times in sub-zero conditions. I could believe this if he meant 0 Centigrade, but can anyone enlighten me if this is possible in Farenheit? It seems like an absolutely wild claim of an unsafe technique to me.

I figure with as technical as members on this site are, I could get accurate information one way or another. Thanks for your help.

[Graham Williams]

Yes, I did mean fahrenheit. Want pictures?

[Shawn Basil]

Yes, I'd appreciate pictures, but I'd also like some more input from third parties on the safety of the practice, which seems to fly in the face of every recommendation from the manufacturers of canister stoves.

As a moderator, I was tempted to pull your post for liability purposes. But since I haven't spent time in high mountains in serious snow since 2003, I have been willing to listen to input on heat exchangers. I've logged several thousand miles in three season conditions throughout the US as well as Appalachian winters since then and this is the first time I've heard of a heat exchanger used with a canister. My instinct is to protect our readers (particularly those who've not used canister stoves) from a possibly dangerous practice which you've presented as common and perfectly safe.

But rather than simply pull it, I've chosen to ask here, where there are a number of diehard stove users who routinely modify their gear to improve performance. I'm genuinely interested in effectiveness and even more in the safety issues involved.

So is there any one else out there who does this? Is this a good idea for a new backpacker who has not dealt with MYOG projects? Is it really a common practice? If so, I'd like to know. As I said, I came here because of the technical nature of folks who camp out here. I'd really appreciate your input.

[Graham Williams]

As I said in the other thread, I'll get some pictures later this week, both of home made and factory manufactured heat exchangers. I might even have a couple of pics of them in action, but that's more dubious, because I don't think I ever cared enough to take a picture of the things before.

Look, heat exchangers are common enough in climbing land, and in a place called Europe, that manufacturers actually make heat exchangers for canister stoves and magazines and books in the United States print explicit instructions on how to make them. The guys who designed the ortik heat it specifically gave the cozy a big throat so you could get your heat exchanger down the side without worrying about the nomex.

Somehow, I think that anybody seeking a lawsuit would go after Climbing magazine's parent company a long time before they went after backpacking.net. Or the mountaineers — Mark Twight's book Extreme Alpinism also explains how to make them. Or Patagonia — they've published how to make them as well in their catalogs. Or …

I've been climbing for ten years. I've been doing winter alpinism for about seven years. I've spent extensive time in the alps, the caucasus and central asia in the winter. I've used a canister stove near the top of mt ararat in december, and believe me it was cold. I've never had a real problem using a canister stove. I haven't tried to colder than -10f, and it might well suck in conditions that cold.

You're also not supposed to cook in a tent. People do it all the time.

[Graham Williams]

"how can it be safe to use the system if the cozy is necessary to prevent the exchanger from "melting gear"?"

You're cooking in a tent or on a portaledge. You know that the dyneema sling you're tied in with will start melting around 200 f, and that the walls of your tent will likewise experience some technical difficulties at that point.

Hence the cozy.

[Shawn Basil]

I understand the concern on melting nylon gear. I was concerned about a piece of copper tubing that hot also causing a rupture with the canister, as you mentioned at the connection point.

The link you showed on TLB helps clear things up though. The written description makes it sound as though you're placing several wraps of copper tubing around the canister and then wrapping a bunch of foil over that which sounds extremely dangerous. The pictures in the "BOMB" link (and yes, I had to chuckle over the name :) )with the flattened tube contacting a relatively small area, and the foil on the cozy, but still allowing the tube to somewhat vent around it look MUCH safer than what I envisioned. I might even be willing to try it on a large stone area well away from my tent.

I'll leave cooking from a portaledge to you. In fact I'll leave the portaledge itself to you. As I said, I haven't done any multi-pitch technical climbing since I left NOLS 4 years ago, and canister stoves were just beginning to really gain popularity in Wyoming. But this was a new one to me. Thank you for the extra info.

[Michael Davis]

While I have seen the practice of applying heat to fuel, I don't feel comfortable with doing it myself. "How much is too much?" I don't want to find out!

I do use a canister stove in cold winter conditions but my solution to improving cold weather performance is to use an MSR Windpro stove and invert the canister.

As excellent articles here on BPL have explained, canister fuel is a mixture of mostly butane and some propane. In cold weather only the propane vaporizes and burns, leaving most of the fuel (butane) in the canister.

By inverting the canister, the vaporized propane forces the butane out of the canister. This only works with a stove that has a tube that wraps around the burner so that the liquid butane is vaporized before it enters the burner. Using this technique, all the fuel in the canister gets used even though it's too cold to vaporize most of the butane and there is no risk of me underestimating the performance of a heat exchanger!

I can see that I can save weight this way by not having to wear asbestos underwear, a flack jacket and a welder's helmet to cook!

[Brett .]

I have read about that technique on old-school websites, but with modern stoves with built-in pre-heat tubes in the flame area, my understanding is there is no need for that anymore, just turn the canister upside down.
Lightest stove Ive found with that capability is the MSR WindPro at 6.8oz.
Is there another reason why heat-exchangers would be necessary, such as extremely low temps?

[Tony Beasley]

I have tested my inverted canister liquid feed stoves after the stove and canister (30/70 mix) have been in the freezer and cooled down to -20ºC (-4ºF) and they worked quite well.

The coldest that I have used them in the field is only -7.5ºC (18.5ºF)

Roger Caffin’s http://www.bushwalking.org.au/FAQ/FAQ_Mixtures.htm site has a lot of information on canister and cold temperatures.

Tony

[Michael Martin]

Hi Guys-

I can't comment directly on the copper wire heat exchanger as I've never used one, but you might want to look at this article that brings it up:

http://www.backpackinglight.com/cgi-bin/backpackinglight/00041.html

Also, inverted canisters have been discussed in dozen's of BPL forum threads. (If you're interested, do a search for "inverted canister" — there's too many to link here.)

Finally, take a look at Roger Caffin's series on canister stoves:

http://www.backpackinglight.com/cgi-bin/backpackinglight/coleman_xtreme_stove_review.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/exploding_gas_canisters_the_hazard_of_overheating.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/stoves_tents_carbon_monoxide_pt_3.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/selecting_stoves_for_cold_weather_part_1.html

http://www.backpackinglight.com/cgi-bin/backpackinglight/selecting_stoves_for_cold_weather_part_2.html

Happy Reading,

-Mike

[Shawn Basil]

Some of this got started on The Lightweight Backpacker forums with a post on whether a hiker getting into his first cannister stove should buy a Snow Peak GigaPower or a JetBoil for a late fall (November) trip in the Montana Rockies in temps possibly down to 0 F (-17 C). I and a number of others mentioned neither stove worked well (and maybe not at all at that temp) without prewarming, and even then performance would drop off quickly as the cannister recooled.

Crackers posted he had success with his cannister stove (I'm pretty sure a JetBoil since he speaks of using it in hanging mode, both for portaledge use and sometimes in a tent in severe weather) by using a heat exchanger. I was very skeptical as I read the linked passage from Climbing Magazine, and was worried that if some new canister stove user tried to make one, the results could be, well, unfortunate.

The links Crackers later provided showed a much more modest copper tube heat exchanger that only touches one side of the cannister and never wraps completely around. I think it could function pretty well and reasonably safely, and in a self-contained system where one could hang the entire system (such as a JetBoil while on a big wall), it would likely be very helpful.

But having never heard of a setup like this, I wanted to get some word from the stove experts here. I already knew about inverting cannisters, applying hot packs or placing the upright cannisters in warm water. But this one was new to me.

Thanks again for the responses.

[Graham Williams]

actually, i use a pocket rocket. jetboils suck imho.

Making a hanging stove is an old climber trick. MSR used to sell a conversion kit that works with most of their stoves. But now I'm going to be using the ortik heat it…http://www.getoutdoors.com/goblog/index.php?/archives/2176-Ortik-Heat-it.html

edit: i wrote superfly instead of pocket rocket and then realized that nobody else calls the thing a superfly, which is an old joke with my climbing partner, not the real name of the stove.

[nanook ofthenorth]

Graham, I was wondering if you had any comments about the Ortik after some use; I'm particularly interested in their warning about not turning it up all the way?

Its too bad your original post got yanked, it may not be standard in the Backpacking community – maybe because for lightweight backpackers there are other alternatives (alcohol or bulkier inverted canister type stoves, ect.)
But I would love to hear an informed discussion on heat exchangers on this website – seems like there could be a lot to learn there for eveyone involved.

[Roger Caffin]

This is where a bit of real knowledge helps. I have covered the area fully in some of my articles on winter canister stoves and exploding canisters. But to repeat here:

You WILL need to provide some thermal feedback to the canister with an upright stove in cold (and very cold) weather to keep the butane above 0 C – or it will kark.

As long as you keep the canister below 50 C, and preferably below 40 C, you will be within the prescribed safety limits for these canisters. If you can touch the canister without going 'ouch', it is at a safe temperature.

Cheers

[nanook ofthenorth]

Thanks Roger, I read your articles and thought they were excellent. I also read up on the Alpine BOMB ect.

I guess what inspired my post was I was wondering about the Ortik again.
Anyone used one of these?

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