Gas canisters and Stoves
Which gas canisters should we use for our stoves?
It’s raining and I’ve spent some of my time refining (and translating) my notes on gas canisters and burners. I thought I’d share it with you guys. Gas stoves are easy to use, light, clean and very safe. But the prices of the gas canisters differ quite a lot, and some of the canisters are better than other in different environments.
This might get a bit nerdy, so I’ll just start with a rough rule-of-thumb: In warm temperatures (above 15°C), the cheapest gas, with a lot of Butane (n-butane) works OK. When the temperature drops, n-butane gets inefficient or unusable. Canisters with added isobutane or propane in the mix will give more oomph. Be aware that most of the isobutane and propane will burn first when using a top mounted burner, leaving the slow n-butane in the canister. In cold weather it might be smart to use canisters with only isobutane and propane. Or switch to a stove with liquid mode (with the canister upside down).
Here's my list and an attached table. (If you see things that are inaccurate, please tell me and I’ll learn and adjust).
Different mixes of n-butane, isobutane and propane
The mix is liquid and evaporates/boils to the gas we hear/smell/burn.
The gases have different evaporation points. In free air at sea level:
n-butane: -0,5°C
sobutane: -12°C
Propane: -42°C
*** E.g. with a temperature of -5°C isobutane and Propane will evaporate ok, n-butane will not.
*** For the burner to work the pressure inside the box must be higher than at the outside, pushing the evaporation point higher (warmer/worse).
The gases have different vapor pressure.
N-butane – low: 215 kPa at 21ºC
Isobutane - higher: 310 kPa at 21ºC
Propane – much higher: 859 kPa at 21ºC
*** I.e. when they all are present, the propane (and isobutane) will evaporate and be used faster than the n-butane (with a top mounted burner), even if the weather is warm. Leaving much of the sluggish n-butane in the canister.
Propane’s high vapor pressure is the reason canisters with pure propane would be too heavy to carry in light backpacks.
When the mix evaporates/boils the canister and content gets colder.
The boiling gas drags energy from where it can – first from the liquid itself (think of how a fridge produces cold temperatures).
When the liquid gets colder, the evaporation slows down and even stops if the liquid gets colder than the evaporation points.
It’s a myth that gas canister stoves don’t function well in high altitudes.
The lower air pressure outside pushes the evaporation point down (3 degrees per 1000m), making the evaporation more efficient. But when you get higher the air temperature often drops. N-butane don’t work well when it’s cold.
When the weather is cold, it might be smart to keep the canisters warm (inside your clothes) and/or add heat to the canister using heat pads or water.
n-butane and isobutane are isomers (variants with different structures) of Butane.
In isobutane, there will always be some n-butane, even if the text on the canister says “isobutane”. Typically 2-6% of “isobutane” is n-butane.
In stoves with liquid mode (canister upside down), the pressure in the canister pushes liquid (the mix of n-butane, isobutane, propane) to the stove.
The mix evaporates outside of the box, using the heat of the burner.
The vapor pressure of propane (and isobutane) will feed the stove with three gases, even if the temperature is lower than n-butane’s evaporation point.
Boiling water using a less than half full canister of Primus Powergas. Typical northern Scandinavian summer’s day. Worked OK, but before the water was boiling the stove actually started to slow down, and I started warming the canister with my hands.
1200m altitude and 10°C. The MSR Isopro canister with 80% isobutane and 20% propane works very well and will continue to do so until it’s completely empty
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This stove can be used in liquid mode. When the burner is heated I’ll turn the canister upside down to make sure the mix of butane/propane (70/30) is burned evenly.
I prefer to use a stove with liquid mode when the weather is a bit cold.
Picture added Dec. 2020: The Optimus Vega using Liquid mode. The gas in the canister pushes liquid mix of Butane/Isobutane/Propane trough the tube. The tube passes trough the flame to add heat and evaporate the gases. This way the stove works and burn even the slowest of the gases in cold temperatures.