Three Points of the Compass looks at a hack that might enable an upright gas stove to continue working in cold conditions. The Moulder Strip is only for ‘extreme cold use’ though and requires great care and is not generally recommended.

Increasingly people are finding ways to continue using gas stoves in conditions where we might once have changed over to liquid fuel stoves. Winter fuel mixes is one way, or some specialised remote canister stoves will permit a canister to be inverted and use fuel in liquid form rather than gaseous. Warming the canister is another way and the simplest methods are covered below. There is also a slightly dodgy hack developed by those venturing into higher and colder elevations that can work for hikers and climbers prepared to accept the associated risks.

A problem with using gas stoves in the cold is the temperature at which gas in a canister vaporises. This isn’t as disastrous as many may make out and there is usually a way round it. Take a look at the side of a canister and it will tell you the exact mix of gases it contains. Winter mixes typically contain a greater proportion of propane though there is an upper limit on how much of this can be incorporated in a standard canister. Each gas vaporises at different temperatures- Butane has to be above -0.5°C to vaporise, Isobutane above -11.6°C, Propane above -41.7°C. So you can see that when the temperature starts dropping below freezing, Butane is the first of the contents to struggle and will mostly fail to vaporise. For Isobutane and Propane however, no problem. As the temperature drops still further, Isobutane will remain in liquid state and only Propane will be exiting the canister in gaseous state, though a few molecules of the other gases will ‘hang on’ and exit with it. This is why you can be cooking or heating water with a normal gas stove a few degrees below freezing and it may be struggling to burn, or it may splutter, even possibly stop, despite a shake of the canister revealing that there appears to be plenty of contents. What will have occurred is that the Propane, and possibly Isobutane, have burnt off leaving the Butane behind remaining in liquid form. The simplest way to try and ensure a gas canister stove works in cold weather is to have the best mix of fuels. Have a look at the contents listed on your gas canister. Some cheaper canisters may have a 100% butane content, which is fine for warmer weather, just not four season. Unless you do something to make it vaporise.

Changing from liquid to a gaseous state takes energy. This is characterised by a gas canister becoming noticeably cooler while a stove is in operation. Insulating from frozen ground, possibly on a piece of plywood, or piece of closed cell foam, or an insulating jacket may help… for a while, as a warmed gas will cool as it vaporises. Warming a canister inside a jacket and against a warm torso, before lighting, will help initially but only works until the canister again drops in temperature. Placing warm hands around a canister makes a noticeable difference, but then cools hands uncomfortably. Another solution is to warm a canister and use the initial heated water in a warm bath, with the canister stood in this. If you have to, peeing in the bath in which the canister sits will work for a while as urine exits the body at body temperature. The simplest method I have seen is a crumpled dish of aluminium foil beneath and around the stove and canister, reflecting heat from the burner onto the canister, however the slightest of breezes will whip most heat away before it can be effectively utilised.

One type of gas stove that excels in colder conditions is a remote canister stove fitted with a generator loop, which enables a canister to be inverted. Note, it is only possible to invert a canister if a generator loop is fitted, this enables a liquid feed to be vaporised in the heat from the burner head. Three Points of the Compass has previously looked at a few excellent stoves that can be used in this way, such as the Kovea Spider and Fire Maple Blade 2. Other stoves might instead have a pressure regulator fitted. Relatively few stoves have these as they are manufactured to fine tolerances and add cost to a product. I have also reviewed a couple of canister top stoves fitted with these, these were the Soto Windmaster and Fire Maple Polaris. The excellent enclosed MSR Windburner Personal Stove System also incorporates one of these. For effectiveness, a generator loop is always going to be a preferred attribute over a pressure regulator, however canister top stoves cannot be fitted with a generator loop.

• Fire Maple Blade II remote canister stove
• Kovea Spider remote canister stove
• Soto Windmaster canister top stove, with pressure regulator
• Fire Maple Polaris canister top stove, with pressure regulator

The Alpine BOMB, or Moulder Strip:

If conditions are exceptionally cold, there is a simple hack that can be used, even with canisters containing solely butane, but it must be prepared in advance of a trip. It involves moving some of the heat from the stove top flame, down to warm the gas canister.

This method should only be used in extreme cold, it is dangerous to use this hack in milder conditions as it can result in an over-heated canister, with potential resultant explosion.

The Alpine BOMB, or Moulder Strip, is a method that I understand first became known in european climbing circles and was written about in Mountain Review magazine and the Mount McKinley Climbers Handbook. It was then known as the Alpine BOMB- “Bloody Outrageous Mountain Burner”. This involved heavy gauge copper wire beaten flat and clamped against a gas canister. Bob Moulder later referenced and resurrected the method, refining it into a simple hack, again, to be used only in extreme cold.

Bob’s method used a strip of thin copper, shaped to conform with the curve of a canister, and held against it by a pad of silicone and Velcro. The idea is to warm the gas canister, not make it hot. This is done by transferring just a little heat from the flame, down a strip of metal, to the canister side. There are a couple of ways of efficiently clamping the strip to the canister, while a length of Velcro is fine, a silicone wrist band is perhaps easier. The metal used by various exponents also varies. As per the original Alpine BOMB technique (that used tubing), Bob recommends copper, others have successfully used a thicker sliver, albeit lighter, of aluminium.

Copper is probably the most effective material to fashion a moulder strip from, but others have successfully used other metals such as the aforementioned aluminium, or steel. Very little is required and eBay, Etsy, craft and DIY shops will supply the necessary material, or just cut down a drinks can. Bob’s specification for the copper strip, as shared by members on the Backpacking Light forum, are “1 inch wide with a thickness of 20-25mil, which is .020″ to .025″. The length of strip will depend on the height of stove used. A short stove will need a shorter length strip than a tall stove.

The example I show here has been curved in the fingers so as to match the curvature of the canister side. This allows the surfaces to touch, thereby improving transfer of heat from strip to canister. Some sort of insulation from the ground below the canister is an easy helpful addition (plywood, closed cell foam etc.). An insulating cosy around the canister can also help things along. Various manufacturers produce insulating cosies for canisters, but they are simple to make with an offcut from a closed cell sleeping mat.

My little strip of copper is sized to fit one of two small stoves. These are the smallest and lightest probably available. This is the cheap ‘n’ cheerful BRS 3000T that weighs just 25g. However a better stove than this is the similarly sized 43g Fire Maple FMS 300T canister top stove. Both are shown here. Other stoves, such as the tall Soto Windmaster, will have longer valve stems and require a longer moulder strip. An image below shows how I have held the strip tight to the gas canister, using a 5g slip on silicone wrist band.

• BRS 3000-T ‘Hornet’ stove, review
• Fire Maple FMS 300T stove, review

Again, this is NOT a three season technique, it is solely for careful use in extreme fourth season conditions. All this is attempting to do is slightly warm a canister. A hot canister is dangerous. It can explode. The intention is just to slightly warm the canister and the gas within.