Canister stoves are simple and convenient to operate, and have long been my go-to three-season option. But they suck in the winter, or any time temperatures start dropping below freezing, when they work poorly to not at all. Why?
It boils down to some basic chemistry and physics. Canisters contain a compressed blend of butane and propane. The pressure keeps most of the mixture in a liquid state (you can hear it sloshing around inside if you shake the canister), though a small amount vaporizes into a gas above the liquid. When you attach a stove to the canister and turn it on, the gas rises out of the canister to feed the stove burner and heat your food or water.
|Why, stove, why??? |
Photo: Michael R Perry/Flickr Commons
In order for this to work, the pressure inside the canister must be greater than the pressure outside the canister. But as the canister temperature drops below freezing, its internal pressure starts to diminish until this is no longer the case and the burner sputters and goes out.
Why? The primary culprit is butane, which stops vaporizing at 31 degrees Fahrenheit (its boiling point). (Isobutane—a chemical variation of butane—continues vaporizing down to 11 degrees Fahrenheit.)
Butane is the primary component in fuel canisters, typically accounting for 70 to 80 percent of the fuel mixture; propane makes up the remainder. Unlike butane, however, propane continues vaporizing even in very cold temps (down to minus-43 degrees Fahrenheit). This has some interesting implications for cold-weather performance.
Among these is the fact that the propane will burn off at a disproportionate rate in sub-freezing temperatures. As the remaining mixture shifts increasingly toward butane, less and less fuel vaporizes until eventually the canister pressure drops too low to continue feeding the stove. This means that a brand new fuel canister may work for a while in sub-freezing conditions, but can stop working long before the canister is empty.
There's also another factor at play that affects a canister's cold-weather performance. The process of vaporization—the changing of physical state from liquid to gas—takes energy. In a fuel canister, that energy comes mostly from the warmth (latent heat) in the fuel mixture itself, which is why a stove canister will become noticeably cooler while the stove is operating. In cold temperatures, this effect can drive the canister temperature down and stop the burner cold—even if the ambient temperature is above the fuel's boiling point.
So what to do? If you expect to do much winter camping, buy a liquid fuel stove that runs on white gas, which works well even in bitterly cold temperatures. If you are out with a canister stove in borderline, near-freezing conditions, warm up the canister before you use it. Stick it inside your layers for a while, or bring it into your sleeping bag at night. Placing the canister in a shallow dish or pan with an inch or two of water can also help keep it above freezing while in use.
- For an in-depth and accessible breakdown of the science behind all this, this FAQ on fuel mixtures is an excellent read.
“Equipped” is an AMC Outdoors blog, written by Matt Heid.
Labels: Cooking, Stoves, Winter