Cannisters Stove Efficiency over Altitude

The air pressure changes however; I am pretty sure the nitrogen to oxygen ratio is the same.  I have done quite a bit of altitude testing with alcohol stoves and I found that they burn a bit slower but fuel efficiency was pretty much the same.  Unsure about Isobutane stoves, however; it may be an issue if you are running them full on.  That being said, most prudent backpackers who are concerned about fuel efficiency throttle the burn rate back by quite a bit.  Long story short, shouldn’t be a problem.  My 2 cents.

Thanks Jon.  My understanding is that there is greater CO production at higher altitude.  I’ve always wondered if this was a symptom of a change in efficiency as well?  I have no reason to think the two are related though!
This is more an intellectual curiosity than anything that would put my trip at risk.

FYI – Roger would prbably be the best person to chime in  on this.

Roger would say that the flame quenches on the fins which cause CO

Just guessing : )

7500 ft is not very high, so I doubt you will notice much of a difference in stove performance. And if you are already accustomed to rehydrating food with 90C water, then you won’t need to change your timing either. When I rehydrate food with boiling water at 12,000′, I generally triple the rehydration time.

The Canadian Rockies are nice. I’ve only been there once (in Alberta), but I really enjoyed being able to hike above timberline with very little oxygen deficit.

Yes, the percentage of oxygen to nitrogen remain the same anytime your feet are on the ground and a considerable height above that due to the mixing of the atmosphere (a.k.a. “weather”).  Only when 99% of the atmosphere is below you (at which point, you’d be dead), does it swing towards lighter species.

Any orifice, as used in all our butane stoves, imparts momentum onto atmospheric air with a jet of butane, mixing the fuel and air at the same time.  But for the same throttle setting, the same mass flow of butane will entrain less air when the air is less dense.  This is why pilots of carburated airplanes are constantly fiddling with the fuel mixture to adjust from the richer (in fuel) mixture at ground level to a leaner mixture at altitude.

TL/DR: Your stove will burn slightly richer at altitude and therefore more prone to carbon monoxide production and slightly lower efficiencies.  That can largely be mitigated by not running it full throttle, which you shouldn’t be doing anyway as a medium flame is more efficient than the largest possible one.

Dan (treeline without low oxygen): My first year here at 60N, I’d keep thinking, “Man!, I’m in great shape, powering up these slopes above treeline without being winded!” until I’d remember that local treeline is 1200 feet, not 12,000 and the bushline only 500 feet above that.

Caution to DavidD: Your usual cues that water is at 90C (bubbles starting, amount of steam) will occur at about 80C, so factor that in if you’re looking for particular rehydration or cooking times or if you’re counting on it to sterilize water (but 70-80-90C are all fine for pasteurization).

Dan, David, thanks.

I modified my motorcycle adding a dynojet kit and free flow air filter to the carbs.  We would ride Mount Washington on opening day and the bikes carburetion would be way off by the top, so the fuel air ratio explanation makes perfect sense.

Thanks for the timing and bubbles tips. I use filtered water to rehydrate but those are both good the know.

I’ve driven through Banff but never had the opportunity to backpack it.  My son is there often, either doing the gdt or rock climbing and his pictures over the years finally got me motivated.  I’ll be there 10 days so will be adding some big day hikes to the agenda as well.   Very much looking forward to it.

Caution to DavidD: Your usual cues that water is at 90C (bubbles starting, amount of steam) will occur at about 80C, so factor that in if you’re looking for particular rehydration or cooking times or if you’re counting on it to sterilize water (but 70-80-90C are all fine for pasteurization).

The small bubble form out of micronucleation sites and the above statement is generally true.  The OP did state that he was using a Stash mug and my experience has been that the HX fins tend to concentrate the thermal energy, and bubbles will form a far lower bulk temperature than with a traditional mug.  It would be prudent spot check the bulk temperature with a thermal probe.  As David said, above 70 C should do it.  My 2 cents.