There have been a couple small discussions of using air horn canisters as an alternative to the standard canisters that isobutane comes in, however there hasn’t been a really been good write up since this post (https://www.reddit.com/r/Ultralight/comments/ja27v6/new_stove_setup_134g_with_28g_fuel/) 2 years ago. I’ve been using one for the past year without issue and just picked up a couple different size options so I thought I would do a little write up.

Full credit to this idea goes to David Thomas from this BPL thread (https://backpackinglight.com/forums/topic/smallest-possible-butane-stove-set-up/#comments), although he credits “JohnK” from a thread I can’t seem to locate.

There are three sizes available from the Emzone brand locally to me at Canadian tire, however they seem to be widely available from a variety of vendors. A 28g, 90g and 156g. All of the discussion so far has centered around the 28g canister, and for good reason, it’s awesome for short solo weekend trips. However, the other two sizes are still worth consideration. As shown in the chart below, they have substantially better gas/canister weight ratio than traditional MSR canisters, but more importantly are just smaller allowing for less dead weight to be carried on shorter trips.

*The weights for MSR canisters are from general internet sources.

There are two reasons that these canisters are able to be so much lighter than the standard ones. The smaller two sizes are made from aluminum instead of steel (this also has the benefit of not rusting, no more rust rings in the bottom of your pot after putting a canister away wet). But the main reason these are so much lighter is the narrow diameter. This reduces the hoop stress meaning a thinner, lighter wall can be used.

The main issue with these canisters is that the small diameter makes them less stable. This is easily solved with a 3d printed stand designed by Jan Rezac over at backpacking light (https://backpackinglight.com/forums/topic/3d-printer-stands-for-air-horn-canister-stove/). It’s designed in OpenSCAD so it’s parametric and easily customizable for any size of canister. I haven’t printed one for the 156g canister yet, but my stand for the 28g canister is 5g, and the stand for the 90g is 8g. These also suffer from having a very small thermal mass so as you get down to the end of a canister, particularly the 28g version, they get cold and tend to lose pressure. I’ve found putting my hand around it to solve this problem quite effectively when it infrequently arises.

All the canisters I purchased come filled with 1,1-Difluoroethane, however they are also available (apart from the 28g, I’m unsure of why) with an isobutane/propane mixture (https://emzone.ca/wp-content/uploads/2021/06/p7-046400___________emzone_sport_signal_air_horn_large_-_156_g_en.pdf, according to the SDS it's a minimum of 40% propane). This combined with the relatively high vapour pressure of 1,1-Difluoroethane (88psi at 25c, lower than propane, higher than isobutane) makes me very comfortable with using these canisters with typical camping isobutane/propane mixes. Here is a photo of the three different sizes, along with my current weekend setup with 28g canister (empty), toaks 550 pot, 3d printed stand and carbon fiber lid https://imgur.com/a/sghSaCN.

When filling these canisters for the first time, it is prudent to empty them completely, and fill partially with isobutane a couple times to purge any remaining difluoroethane. You also need to keep a pretty close eye on them when refilling and not fill past their respective weights. If you do fill past it, vent it immediately down to the proper level. Some head room must be left as liquid butane, and particularly propane have a high coefficient of thermal expansion meaning that as the temperature increases, the head room that you have decreases significantly. A rule of thumb for propane cylinders is that they get filled to 80% of capacity to accommodate for these variations.