The Evolution of a Winter Stove – Part 3

[Stephanie Jordan]

Companion forum thread to:

The Evolution of a Winter Stove – Part 3

[Michael Martin]

Ahhh, that makes sense. Thanks, Roger. I sold my Xtreme years ago when it became hard to find fuel so I haven't had one in my hands for a while. :-)

Like you, I've been trying to find/build the "perfect" winter stove for almost a decade. I've finally settled on a regular old sit-on-top canister stove with a bit of super secret tricky technique involved. ;-)

The trick is to stomp out a snowpit, say, 50cm in diameter and 50cm deep. I make sure the canister is prewarmed with body heat to get the fuel to initially vaporize. I lower the stove into the pit, light it, and let her rip. The volume of the pit is small enough that the stove heats it to 40-50F even when the outside temp is as low as -15F. (I've verified this with thermometers). The snow also buffers the pit temp by melting if it gets too warm, reducing the chance of thermal runaway. If it's windy, I'll partially cover the pit with a sleeping pad while cooking. The canister stays warm enough in the pit (well above 0C) to easily vaporize the fuel. The canister itself is plenty stable on the compacted snow, so I don't need any kind of stove platform. The pit makes a superb windscreen, so I don't need an aluminum one like I would with a remote canister stove.

I've used this technique snow camping since 2007. I don't know what the lower ambient temp limit is, but I've used it successfully down to -15F with my old, faithful Giga stove and down to -5F with a Jetboil Sol. The Jetboil works particularly well as all the parts are connected and it's easy to lower into the pit. It does waste less heat than the Giga, though, so doesn't warm the pit as much and likely has a higher low-temp limit.

Cheers,

-Mike

Disclaimer: The above describes my personal stove technique. There are risks such as CO emissions in a reduced-oxygen pit, possible canister overheating/explosion, weather conditions that make it impossible to use, and the risk of the system failing and leaving you with no working stove system. Attempt at your own risk.

[Roger Caffin]

Hi Mike

Stove pit …
I learn something new every day!

Mind you, stomping a hole that deep in Australian snow might be a bit more difficult. It tends to be horribly solid. Even so, NEAT!

Cheers

[Michael Gillenwater]

I'd be a little worried of the CO output of this setup.

[Franco Darioli]

Michael,
Very simple , very clever… after all that is how a snow cave/igloo works.
Thanks

[Bill Townsend]

For us non-mountain folk, with your low profile is a true windscreen needed? I used to just lay my pack (or myself) on the windward side when the powermax stove fuel was still available here in the us. In snow, I use my caldera as a wind screen, just not closed up, I simply flip it over and jamb an inch or so of it into the snow/dirt leaving it open like a normal screen, got sick of using other alternatives. Been looking for a well thoughtout, and what appears to be a "universal" canister stove, weight is good for the type of stove, an ounce extra (if that) to use any brand canister you find is worth it. Well done Roger!

[peter vacco]

FANTASTIC !

all i can add is that if one desireth to deburr plastic parts, a fast way is to dust them with a propane torch flame.

[James Marco]

Hi Bill,
Yes, wind screens are still necessary. They actually serve two purposes.
1) Shield from winds
2) Trap and concentrate heat output from the stove

Ignoring the first part 1) above, the second part is what is missed. Rather than distributing heat in a 180 degree arc, roughly speaking, it is trapped and sent back to heat the pot. As a corollary, any heat lost around the edges of the pot is also reflected back to the pot. Heat is produced in two parts: convective and through infrared radiation. Convective heating is through exhaust products and heated air that is not combusted. Infrared radiation acounts for a large portion, though.

Discussing convectition first:
I do not agree with a strict 3/4" gap around the top. This allows too much heat to be lost for no productive purpose. Conversly, too narrow of a gap will form a heat "puddle". The puddle will force heat down, into the combustion and stove. This is not what we are trying to heat, rather the pot, and what it contains, is the target. This will also increase CO production.

From this reasoning, I believe that a variable gap is needed. Depending on the setting of heat output you are using, anything between a 1/4" (on very low) to 3/4" (on high.) This will match the combustion products flow rate with their actual production. This assumes that air input is about 3-5 times exhaust output. Input is less important than output, however, so a good sized opening larger than needed will always work well. It also allows the air to cool the lower stove components.

Also, not all the heat is transfered upon contact with the pot. Some will be, some will not. Some will be picked up from the pot. This is usually carried away in the flow.

For infrared or radiative heating, using a wind screen made of aluminum or some reflective material alows the radiation to be reflected back to the pot rather than lost. Painting your pot black helps with this.

Using windscreens helps by about 25-30% given still air. In winds, they will help a lot more.

[Ethan A.]

Beautiful work Roger, along with an excellent article on the product development.

Is there any chance the toilet paper filter could be compromised by moisture from high humidity or water from rain getting into the jet and deforming the filter?

Should the TP filter be proactively changed every X number of uses?

What would be a sign that the TP filter has been compromised (allowing gas to flow through but not catching contaminants)?

[Forrest G McCarthy]

Cool looking stove. The next step is producing a reusable ultra-light fuel cylinder like the carbon composite cylinders used for paint ball guns and oxygen on Everest.

Carbon composite cylinders are already in production. Designing a lightweight DOT approved valve is the crux.

http://www.luxfercylinders.com/products/alternative-fuel-cylinders/443-type-3-alternative-fuel-cylinder-specifications

[Roger Caffin]

Hi Bill

> For us non-mountain folk, with your low profile is a true windscreen needed?
There's no magic here, just two points to watch.
* If the wind blows the flames sideways much, they won't be heating the pot.
* If the wind blows the hot air away, it won't be heating the sides of the pot either.

For that matter, what James wrote is equally appropriate. So anything which protects the stove is fine. Yes, I have used rocks, packs, boxes etc instead. But the extra IR reflection from a metal windshield adds a bit.

> I simply flip it over and jamb an inch or so of it into the snow
Um … that's rather clever!

Cheers

[Roger Caffin]

Hi EJ

> any chance the toilet paper filter could be compromised by moisture from high
> humidity or water from rain getting into the jet and deforming the filter?
Um … if you are getting rain inside the burner tube and through the jet, you may be taking outside cooking a bit TOO far! Humidity – nah, wouldn't worry. It will dry off pretty quick when the stove is running.

> Should the TP filter be proactively changed every X number of uses?
The ideal answer might be yes, but … what is X?
If the canister is very clean (eg Coleman powermax) then X=100 is reasonable.
But if the canister is one of those Chinese ones I tried to use (once), then X < 1. The Chinese canister was full of very fine dust, and everything blocked immediately.

> What would be a sign that the TP filter has been compromised
Hum … if you can't get a decent gas flow, then the TP might be rather blocked. Bad (dirty) canister.

Cheers

[Roger Caffin]

> Carbon composite cylinders are already in production. Designing a lightweight DOT
> approved valve is the crux.

I suggest that using a Lindal valve is the OBVIOUS solution here. That gives compatibility with every other canister AND stove on the market. Otherwise you would have cylinders with no stoves.

In addition, you might then be able to get cylinders rated for 100% propane, like the existing Sievert ones. Oh boy, winter fuel!!!!

Cheers

[Josh Brock]

I just sent the link to Fire Maple Stove company and they are going to have a production model of this soon for half the cost…..JK

but seriously how long do you think it will take them to completely steal this stove? Given that some of the parts are already theirs and the excellent detail in which the engineering is described.

[Roger Caffin]

> how long do you think it will take them to completely steal this stove?
I have no idea.
Yes, I use a Fire Maple burner, and I know the designer at Fire Maple. But my article does not specify ALL the fine details which are essential to making the stove work.

If they want to negotiate with me later on, that's fine.

Cheers

[Josh Brock]

"But my article does not specify ALL the fine details which are essential to making the stove work."

I see…. Smart you left out the part that keeps it from shooting fire balls at the user.

[Daniel Tetreault]

Hi Roger,

I've been following your series on BPL for a while now. I'm excited about trying the stove out in the Canadian shield. I do some winter camping and have a lot of camping buddies that are pursuing every last gram.

I know you're still in development, but has Kick Starter crossed your mind? You could set your threshold at enough to cover the cost of all the production level tooling to pump these babies out + whatever other expenses you need per stove to get it done.

I'd be in for a reward level that includes a stove and brings you one level closer to production.

Dan.

[Roger Caffin]

Hi Daniel

> I'm excited about trying the stove out in the Canadian shield. I do some winter camping
You need to email me direct with some details.

> has Kick Starter crossed your mind?
Actually, it never crossed my mind. At present it's a hobby,(albeit a shade odd) but Kickstarter would change that a bit too much for my liking at present. If the stove turns out really popular I wouldn't need the Kickstarter funding; if it isn't then I don't want the hassles of a Kickstarter failure. I have the CNC, and it is a very rugged unit able to handle the workload.

Cheers

[James Haithcock]

Great articles. If your keeping a list I would be interested in the FMS-300T.

[Roger Caffin]

Hi all

I have spent a couple of days experimenting with a modified design for the legs, and especially for the pivot in the middle. Up till now the stove body and the canister connection had been my main focus. Understandable (imho), but that meant that not enough R&D had been done on the legs – up till now.

A casual observation on my desk while fiddling with a stove gave me an insight into how or why the stove 'wobbles' under load. This led me to see that a huge improvement was possible by adding a simple titanium washer in the right place. After all, adding titanium is always good – right? So I did the experiment, and it works great.

The 0.8 mm thick 'tripod' legs are made of a good alloy (5251 H34) and it seems that the only 1 mm sheet locally available is made from a lesser alloy (5052) which is not much stiffer but is a lot harder to machine cleanly and at speed. For the present I will probably use the good 0.8 mm alloy, as it now gives good stability.

At the same time I will modify the design of the legs themselves just slightly, to create an 'opening tab' at the outer corner. When the legs are all folded together it can be a problem separating them out again. The little tabs at the outer corners are now bent apart so the legs open easily.

As a result I think I will probably withdraw the 'centre support' design from production. If the centre-support legs get at all bent the stove can and will rock. My thanks to several readers who pointed this out to me: you were right. I will upgrade all stoves to this new and better design.

Cheers

[al b]

Congratulations on the valve and stove design.

Your valve seems very clever: could it become a new standard for commercial stoves?

Could you license it to manufacturers?

[Roger Caffin]

Hi Alan

> Your valve seems very clever
Um … I am going to guess here that you are referring to the shut-off valve in the canister connector, not the one in the stove body.

> could it become a new standard for commercial stoves?
> Could you license it to manufacturers?
It would be nice to think it could be widely adopted, but it adds complexity to the manufacture. Never mind the improved safety and control – that jacks the price up. Would any of the Western stove 'manufacturers' or their Asian factories pay me for the rights?

I may be getting old, but I can't help being a shade cynical. The best ideas for those guys are the pirated ones they don't pay for. Mind you, I am open to any approaches.

Cheers

[Greg Mihalik]

Roger,
Not only cynical, but complacent.

You should close with "I'm just waiting for a deep pocket company to rip it off so my lawyers, willing to arbitrate on a contingency basis, can negotiate a fair and equitable deal for all."

[Roger Caffin]

>You should close with "I'm just waiting for a deep pocket company to rip it off so my lawyers,

One does not have to tell them everything in advance…

Mind you, MY idea of 'a fair and equitable deal' might differ slightly from theirs.

Cheers

[Jerry Adams]

Presumedly, you have put a defect in the publicly released version that will cause it to explode occasionally.

You'll only release the good version if they give you fair and equitable deal.

[Author]

Posts