A picture says more than a thousand words, so I uploaded some.
You can find the pictures by visiting my profile, and then looking at my photo gallery; don't know how to put a direct link here.
I also added some more detailed descriptions too in case anyone wants to build one themselves. If you do, please let us know how it goes!
It looks awesome!
You're right about needing at least one baffle plate to prevent the hot combustion gases from disappearing straight up the chimney. On my wood-burner there is a plate so that the gases have pass along under the baffle plate to the front of the firebox before rising and travelling back along the top of the baffle plate to the chimney port at the back. So the gases need to complete a s-bend in the wood-burner before passing out, hence having more time to burn and to transfer heat to the ammo box and heat your tent.
thanks, it feels even awesomer when sitting in front of it!
Also thanks for your thoughts, much appreciated.
Are you talking about a wood burner for your house, or are you referring to a mobile one for van / tent / tarp??? I had a good look at several house log burners, and they all seem to do exactly what you suggest.
Will def try a damper. Re the baffle plate(s): I just got the idea to make it asymmetric in order to make one long side of the stove hotter than the other, meaning a geometry that forces the flames close to one wall, but not close to the opposing one. That would help a lot to radiate more heat towards the centre of the shelter, and less towards the closer fabric wall where it is unwanted anyway, and a waste, too..
In one of the photos you can see white sharpie lines on one long side of the box, outlining a large rectangle. That's where I was thinking of even putting in a window (the glass from cheap 230V work flood lights from the hardware store is thermally resistant enough). That would radiate a lot more heat to the farther end of the shelter, since it would directly let out the infrared instead of just relying on convection. I don't think I'm going to do this now though, as nice as it would look - the walls of the box warp when they get hot, and straighten again when they cool down, which would put strain on the glass or would require a very strong and heavy frame. Also, it's additional weight, and it's a fragile thing to have to take care of. Probably not worth it. Although, for a van stove that might be really nice and feasable! Yet another cool application.
I found out today that pink batts are not nearly as heat resistant as I hoped they would be, and neither seems to be polyethylene sheeting.
I wrapped one sheet of pink batts around the chimney as a make-shift way to pass the chimney through polyethylene-sheeting (read: silage) of a basic proof-of-concept shelter that I made up quick and dirty without melting it.
Err well... lit the fire, and the shelter started to get quite cosy within about two minutes, but as soon as I had taken my jacket off, an intense smell of melting and smoldering plastic started and quickly got worse, which forced me to evacuate. While in a test it was impossible to actually set alight, the pink batts material had started to melt around the chimney nonetheless, and so had the polyethylene, although it was still a good 20 centimetres away from the chimney.
That brought up a lot of good questions though: How the heck do the manufacturers of such tent / stove combinations, for example Kifaru, manage to reliably protect the tent? They run the chimney through glass fibre fabric, which replaces part of the tent fabric, so no tent fabric gets closer to the chimney than maybe 20 cm. But is nylon really that much more heat resistant than polyetylene? I can't imagine that. The answer might be that their chimneys are less hot due to using a baffle. But if the correct baffle adjustment is the only thing between you and a melting tent, that's not a lot of safety margin is it. Or is my stove ridiculously more powerful than theirs? I can't imagine that either.
From my experiments, I am getting the very strong feeling that while they certainly have evolved their designs to a very high level of quality, there really just is not that much room for error nonetheless. It will always be a compromise between safety, living space in the shelter, and weight of the whole setup. For example, if you look at the Kifaru supertarp/superhooch, or even more so the smaller version of it: They sell a front door for it which has a chimney port. Now they do recommend to move the stove a bit further away from the pretty steep - almost vertical - front door, so the chimney is at an angle. But still, in some storms I have experienced, it is a bit optimistic to hope that an almost vertical piece of fabric will not get too close to the stove which, judging from the pictures, seems to be pretty close to it even without wind, maybe half a metre to a metre at most. But then, if you can't use the stove in a storm, that would really be a bummer, because that's when you might need or at least want to use it most.
That also explains why they positioned the chimney port of the Sawtooth shelter further away from the wall at the expense of living room. The Sawtooth is much higher than the supertarp, so the fabric will move even further in wind.
A basic fact seems to be that if you want to be able to use a stove in a shelter safely, you will have to have a larger shelter; the stove needs its own "living space", otherwise it seems too risky to me.
With lightweight fabrics, that's not a problem though. Maybe the increased footprint of the shelter can be an issue in some locations, but they are still making pretty good use of space.
All this is not deterring me from the idea of heating a shelter with a stove at all, it just shows that it is something that you really have to think through properly, and do responsibly and carefully. Not paying attention to what you are doing could have pretty bad consequences.
Modern tent fabrics do NOT go up in flames just like that; I'm not too worried about the fire of a burning tent. Quality fabrics tend to smoulder and melt and stink a lot, for minutes even, before they actually start to burn with flames, if they even do that at all.
BUT it would still mean that you could suddenly find yourself, your bedding, clothing and all other gear exposed to a violent rainstorm without a shelter - since in serious wind, once a bigger hole has been melted into the fabric, the shelter will likely go to shreds starting from there.
Another question that only testing will answer is: Can wind and gusts push into the chimney to push smoke out of the stove and into the shelter? How likely is that to happen? The draw of my now 1 metre tall chimney is absolutely fierce, so it would take quite a bit of wind to counter that, but still.
Also, the idea of "pointing the tip of the supertarp into the wind" so the chimney, which by design of the shelter MUST be on a lean, would lean away from the wind is kind of a nice theory, but in the mountains we have often encountered rapidly and erratically changing wind directions, especially in strong winds, and not only above the bushline. I would not want to rely on a wind direction staying more or less the same for a whole night, not even a few hours. But if the chimney leans at an angle and it leans INTO the wind, the wind WILL blow into and down through the chimney... A chimney has to be vertical I think, full stop.
Again, I'm not deterred. Lots of people in northern America camp with wood stoves in their shelters, so it must work well if done right.
To be continued...
Matt, I've got some spare fire-proof fabric from my dismantled night store heater but it could be dangerous asbestos stuff...If it's any good to you or you want to check it out, give me an email. Be good to see what you've done so far. I've also adapted a rectangular fly to be pitched on the diagonal in the bomb-proof tarp adaptation.
pink batts are mostly fibreglass but are held together with a plastic resin. fiberglass for flame shielding does not have this resin.
Its also this resin that is responsible for the itching that batts used to create. The formula used now is far more friendly