The purpose of this article is to present to the reader several different methods that can be employed to keep fuel warm during canister stove operation in sub freezing temperatures.
I will first offer some basic information about canister fuel which might be of interest to those that are somewhat inexperienced in its use.
The commonly available fuel canisters used for camping and backpacking contain some combination of three fuels - propane, iso-butane, and n-butane. These have somewhat different physical properties, but they all yield about the same amount of BTUs (heat) when they burn. These gases are compressed into their (mostly) liquid form when inside the canister, and when the stove valve is opened the vaporized form of the gas is allowed to escape the canister. We ignite this gas and start boiling our water or cook our food.
Recent experiences suggest that an increasing number of canister brands also contain higher order hydrocarbons, heading into the wax category, and some fine dust or dirt. the amount of 'refining' being done seems to be falling, especially in China.
The main difference among the three gases is the temperature at which the liquid vaporizes into the gaseous state, which is required for us to burn it. The following is a list of the three gases and the vaporization temperature of each at sea level:
|Propane||-44 F (-42 C)|
|Iso-butane||+11 F (-12 C)|
|n-Butane||+31 F (-0.56 C)|
As you can see, n-butane is rather useless in below-freezing temperatures as it won't vaporize. For this reason I find it important to not use any fuel that contains n-butane. In summer it is fine, but not in winter. We want as much propane in the canister as possible, with the rest being iso-butane. There is another fact to be aware of - these vaporization temperatures become lower as one goes up in altitude as the reduced atmospheric pressure allows the gases to vaporize more readily. For example, iso-butane vaporizes at +2.3 F (-16.5 C) at an elevation of 5400' (2,550 m).
Also, there is something else to consider. When the fuel ‘boils’ from the liquid state to become a gas, it robs heat from the canister. This is called the latent heat of vaporization, and the heat loss happens automatically. So the canister cools itself when the stove is in use, and it will become colder than the ambient temperature.
We can now see that there are two conditions which we must overcome - the ambient temperature, and the self-cooling of the canister. There are numerous ways we can accomplish this.
Overheating a fuel canister can have dire consequences, including serious injury, death, and forest fires. The U.S. DOT requires that these fuel canisters be safe to be transported at temperatures of up to 50 C (+122 F). In common field use, if a canister is too hot for you to comfortably touch (over +104 F or +40 C), it must be cooled down immediately. This is known as the 'touch test'. See our article on Exploding Gas Canisters for more details. You are on your own to assure that you don't overheat a canister and cause it to explode.
Techniques for Warming
The following is a list of various techniques that have proven to be effective in warming a fuel canister. Some are superior to others, and this will be discussed as I describe each technique individually. Keep in mind that warming a canister is usually not necessary at ambient temperatures comfortably above freezing.
- Carry the canister during the day in your pack near your back.
- Store the canister in a warm coat pocket, or sleep with it at night.
- If you have a campfire, place the canister and stove close (but not too close) to the fire.
- Warm the bottom of the canister with a small butane lighter; a candle will work as well.
- Use a water bath.
- Place a hand warmer under the canister.
- Employ an IR reflector screen.
- Employ a 3/4 windscreen.
- Employ a copper heat exchanger strip or wire.
- Use a remote inverted canister stove.
We will look at each of these in some detail. But whatever you do, remember the touch test.
Carry the canister during the day in your pack near your back
Your back is at least warm, if not sweaty-hot at times. The water in a bottle carried inside your pack against your back stays liquid, doesn't it? So a canister placed next to the bottle will also stay warm. Well, until you take the pack off, then it will all start to cool.
Store the canister in a warm coat pocket, or at the foot of your sleeping bag or quilt
This is especially useful if you have just taken the warm canister out of your pack. The canister should be functional right away, but it will slowly cool and will need to be re-warmed. This may not be a sufficient solution when you need to melt a lot of snow, which takes a good amount of time and can lead to significant canister cooling.
Place the canister and stove near a campfire
This works of course, but you must monitor the canister's temperature while it is near the fire. It doesn't need to be over +50 F (+10 C). Consider placing a thermometer next to the base of the canister to be sure that it doesn't overheat. An advantage of using a fire is that no extra equipment is needed, but you need a campfire to do this. This might be a problem when you first get out of the tent and you want your coffee RIGHT NOW! (Or if there is a howling storm outside).
Warm the canister with a lighter or candle
This adds enough heat to get the stove started. However, you would need to be constantly adding heat to the canister this way to keep it warm enough to overcome its self-cooling. A candle will work well if your stove is suspended at the proper height above it. This leaves your hands free. If you rely on a lighter, note that most disposable lighters are fueled by n-butane, which must be kept warm in your pocket. They don't work below +32 F (0 C). However, warming the bottom of the canister with a lighter will allow the stove to run long enough for other techniques (# 6, 7, and 8) to take over.
Use water to warm the canister
As long as the water hasn't frozen it will keep the canister warm enough to vaporize iso-butane easily, and if the water is warm enough it will also get n-butane going. Propane will be fine regardless. That is, until you deplete it.
You can use anything you like to hold the water: your dinner bowl, a large cup or a lid off something else for instance. The photo above shows a Jetboil bottom cup: this needs about 4 fl oz (~120 cc/ml) of water for a 4 oz (110 gm) canister.
You could also use a plastic lid that exactly fits the bottom of the canister to seal in some water. Invert the canister, pour water into the concavity, and secure the lid onto the bottom. This will keep the canister warm for a good while. It has the advantage that warm water won't be cooling by evaporation in very cold conditions. The bottom of a 110 gram canister holds about 2.0 fl oz (59 cc/ml) of water; a 220 gm canister holds 3.0 fl oz (89 cc/ml). You could have a dedicated small bottle that you can re-fill and keep warm in your pocket. If you will be melting snow you will need to occasionally replace the water with some that is warmer. With both of the these techniques it is best to have a base to insulate the canister from the cold ground, which acts as a heat sink.
Your urine is both warm and sterile, and it works great to warm a canister. Some people might have an aversion to this approach, but it is good to remember in the event of an emergency.
Place a hand warmer under the canister
Include an insulating base with an air-permeable layer on top to allow air to get to the hand warmer (carbon felt works well for this, as does a layer or two of 300 weight fleece). One disadvantage is the weight of the hand warmers themselves (.75 oz or 21 gm each), which need to be carried out as trash.
This shows the base components (plastic lid with 1/8" evo foam, a piece of carbon felt, and the hand warmer in the white packet) on the left, and a canister/stove atop the hand warmer and base on the right.
I prefer to use one of those cookie cup lids to secure the hand warmer inside the canister's bottom concavity. Several perforations are placed in it with a paper punch, to create the ventilation (oxygen) needed for the hand warmer to work.
I've found that the use of a hand warmer will raise the temperature of the bottom of the canister by 20 F (11 C) over ambient, which will allow a propane/iso-butane canister to function at +10 F (-12.3 C). Various brands will remain active for 5-10 hours, which will easily get you through a lingering dinner meal.
This technique works best if you use a canister cozy, which helps keep the heat in. One can be made from bubble wrap or Reflectix, carbon felt, thick fleece, closed cell foam, or neoprene. You should cover the outside with duct tape (or packing tape) when using bubble wrap or Reflectix (for durability) and also for carbon felt or fleece (to prevent air permeability).
Advanced Warming Techniques
The remainder of this article is accessible to Premium and Unlimited Members only, and contains descriptions of more advanced warming techniques, including:
- The IR Reflector
- A "Safe" Canister Stove Windscreen
- A Copper-Strip Heat Exchanger
- Remote Inverted Canister Stoves
- Guidelines for Using Different Canister Stove Warming Techniques in Different Conditions