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Tiny Wood-burning Stoves

 
Posts: 274
Location: Brendansport, Sagitta IV
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For many years in Montana I heated a 21 foot travel trailer with a sheepherder's stove (miniature cookstove -- cast-iron top but the rest was sheet metal). In the way of old trailers, it had thin walls and very little insulation. The stove had a firebox about the size of a large shoebox (IIRC it was 6w x 8h x 16 inches). The pipe went out the wall (replaced a window) and had two right-angle bends, and the cap was about a foot above the roof. Heat circulated around the stove's oven before going up the chimney, so it was fairly efficient for heat transfer (the main flue rarely got really hot). Quite good for cooking and baking.

In mild weather I burned deadwood, construction scrap, even bones and rolled paper (tho that's a pain to keep lit). This was all free salvage. Riverbanks always have lots of standing deadwood. Cottonwood is my favorite as it burns steady, has high heat value for its weight, and leaves almost no ash. You can bank cottonwood down for an overnight fire without making a lot of creosote; other woods will gunk up your chimney unless they're burning fairly hot. Don't burn bark if you can avoid it.

In cold weather I burned coal. This requires a wood fire under it to start it, but once it's started going to coals, it can be banked down for an overnight fire (a banked block the size of your head burns about six hours). The quality of coal heat is much better than wood heat -- the same temperature feels much warmer. The main drawback is that it's extremely dirty, the smoke is to gag you, and about twice a year I had to open up all the littte stove accesses and one of the pipe elbows, and shovel/scrape out the accumulated ash and residue. Coal smoke makes a ton of deposits -- not flammable but really a pain since they grow like fingers on every surface the smoke passes by. On the plus side, strip-mined bituminous coal is cheap; only cost me about $100/year to keep my trailer as warm as I liked. I could easily keep it 80 degrees in there even when it was -40F out. (Once it got below zero, wood couldn't keep up.) Actually the main problem was that it tended to be too warm (and every so often would wake me up by getting more enthused than necessary, but you can throw water on it and slow it down without extinguishing the fire). Burning coal in an open firebox is a black art in more ways than one.

And of course there was the year all I could get locally was crappy lignite (no good for this kind of stove, won't stay lit and has poor heat value) so had to trek all the way down to the mine in Wyoming to get good coal. (Tho it was free for the picking from the side of the road.)

The trailer came with built-in propane heat (a fullsized wall furnace, not the kind they have now) and that was untenable. The propane furnace had to be turned all the way up to keep it halfway warm, and it was very expensive considering how small the space was -- required about 15 gallons per week. And that was with fully adjustable flame, much less costly than they are nowadays with the flame that is only ON or OFF. (For comparison, when I lived in a Real House in the SoCal desert, I once figured out that my wall furnace, at far-cheaper bulk propane rates, cost me $3 every ten MINUTES.)

I did use the flowerpot-on-the-propane-cooktop trick for supplemental heat in mild weather; that uses very little propane and is no more unsafe than cooking with it. But freestanding unvented propane heaters in an enclosed space will kill you.

If I were doing it today, I'd probably use one of those woodstoves the size of a large overnight bag, with a flat top suitable for cooking, and heavy cast-iron sides; Tractor Supply sells 'em for about $300. They can burn wood or coal and the firebox is big enough to take reasonably-sized wood. My neighbor had one of these and used it to heat about twice as much space as I had (but also with no real insulation), and man was it toasty in there. Too big a stove in such a small space and you'll have a lot of trouble with keeping a good fire going without also roasting yourself. Mine was about as big as necessary for coal; could have been a little bigger for wood. (Cost me $20, so no complaints.)

As to the uninsulated metal walls -- as is that's going to be impossible to keep warm. You need to insulate it on the inside any way you can, and outside block the wind as much as possible. Corrugated cardboard and sheet styrofoam on your inside walls are both excellent for the purpose. Old mattresses, blankets, and pillows also work well. Pretty much anything that covers the wall and traps a layer of dead air will work, and you won't spend all your wood heating up the outdoors. If your flue sticks up a foot or so above the roof, and you anchor it with a bit of wire, wind won't be too much of a problem (at least it wasn't for mine, and I lived in a high wind area, 40mph steady with 60mph gusts not uncommon. It was on the downwind side of the trailer, which probably helped.)

Last place I lived in the trailer, I piled straw bales all around it. That's a common trick for folks in old trailers here in Montana -- so long as the straw stays dry, it's excellent insulation. (Wet it still insulates, but it molds.) But if you're burning wood be sure sparks can't hit the straw -- it can smoulder for weeks before it suddenly decides to make flames and go WHOOSH. If you're in a more permanent situation, dirt works great. Doesn't even need to be a thick layer. I think ideally I would put plywood in a lean-to arrangement, and pile the dirt against that -- that way you don't have moisture against the walls, and there's a big dead air space.

Now I'm an old fart and live in a real house just like a real person, but when I was a young'un, I thought my little trailer was the bomb, and loved the idea of turning a shipping container into a house. Do come back and let us know how it goes!

 
master pollinator
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thomas rubino wrote:There really is no good excuse for causing your own chimney fire.
But people have been doing it since your great grandfather's time. Is the excuse you'll hear...
That doesn't make it smart or right.    



I strongly agree with thomas. Any chimney fire is hazardous. Multiple chimney fires are bloody dangerous. There will be consequences.

This is not the way to manage a wood stove system. It takes good fuel choices, thoughtful operation and careful maintenance to operate a stove safely. This is the price we pay for burning wood.
 
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And of course the best way to manage a wood heat system is to build something like a rocket mass heater which prevents creosote formation in the first place, and does not require constant care to be safe, efficient and effective.
 
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D Nikolls wrote:Ventless propane is NOT your friend. Especially in a seacan. Bad idea.



More ways that one. Its a good heat source but.... Without proper venting within an hour the humidity will be thru the roof and in an uninsulated can all that vapor will condense on the metal walls. Be like living in a waterfall. :)
 
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Location: Linneus, Me.
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Thomas, perhaps you can answer a question that I wonder about:  I heat with a wood stove and I have a flue thermometer attached about 18" above the stovetop.  I have seen advice given on various forms that says to burn a hot fire in the morning in order to burn out any creosote that might have formed in the flue/chimney.  To me, a hot fire means burning the stove such that the flue thermometer approaches or just touches the overfire mark.  But how can that burn out creosote?  Would it not take a chimney fire to burn out creosote?  I never burn my stove overnight, but I do a hot fire when starting up each morning.  I keep the thermometer at the border of overfire for about half an hour.  It also heats up the space nice and quick.  Is it really doing any cleaning of my flue and chimney?  Note that I have a single wall flue going up about fifteen feet in the center of the house and then into a double-wall through the attic and out the roof.  Over the past three years, I have never found any creosote when cleaning the flue and chimney.  I find powdery soot, but no flakes or shiny stuff.  Thank you.
Flue-thermometer.jpg
[Thumbnail for Flue-thermometer.jpg]
 
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Hi Alden;  Your running your stove perfectly.  By having a "hot" fire you are drying and powdering any creosote that is trying to form. It simply falls back into the stove and burns again.
In my house I have a similar set up with single wall to the roof and metal bestos thru the roof.
The house fire burns all winter. It never truly goes out.  Several times a winter I remove my chimney cap and clean the creosote from it.  
I also from time to time bang on the single wall and can hear the dry chunks falling.
I haven't run a chimney brush thru the chimney in 30 years.
 
Douglas Alpenstock
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Alden, creosote is a solid when cold. But it turns into a goo that will slowly flow downward when heated for a long period, ultimately (and ideally) back into your stove to be burned. That's not always enough (regular check/clean is still mandatory) but it seems to help.

Edit: I think creosote flow would be pretty hard to achieve in a single wall pipe, except very close to the stove. The heavy double-wall insulated pipe is another matter, and when you look at how the sections fit together you notice the lip mates up in a way that directs flow downward into the next section.
 
pollinator
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Converting to celsius, I find that your winter temperatures are -6 and you'd like the house to stay 10-15°. That seems doable to me.

We have a 20x14" cast iron stove. Just a metal box, nothing fancy.  Our house is 12x16' with almost as much window as wall. The house is insulated, but some of the double paned windows aren't sealed anymore, they're all drafty, and we still haven't got around to finishing the doors. There's a 1/4" gap around one side of one of them.

Last night was about -5°. I damped the stove down before bed at 9 and let it go out overnight. It would have burned out less than two hours after. When I got around to lighting the stove this morning around 8 it was 13° inside. Last night was not windy, though.

Our first winter here, we didn't get the floor insulated until mid January. The house is up on piers and not skirted. That was a very cold winter for us, down to -20 at night and rarely above -10 during the day. We were burning damp, punky wood and being skimpy about it cause we didn't have a lot. As long as we were at home, the house stayed well above your minimum of 10°. Left empty all day, we came home to frost on the floor in the corners of the room.

I also wouldn't touch propane. I'd pile straw bales on at least the wall facing the wind and keep sparks in mind. It probably won't be your best winter, but you'll appreciate every upgrade that much more. On windy nights, we still get gleeful lying in bed thinking about how we're not in a tent anymore.
 
Jan White
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Oh, I also wanted to mention chimneys. I've only had our current set up, so I don't have a lot of experience. I'm always baffled by people talking about how lighting a stove is such a hassle, though. In our place, you lay your fire, throw in a match, and walk away to a roar. The whole process takes five minutes. I'll often light the stove two or three times a day.

We live in a windy area and never get smokeback, even when the stove is damped down. I like to think it's because our chimney is inside. We have single wall pipe coming out of the back of the stove, switching to double wall where it goes past the edge of the loft (too close for single wall), finally switching to insulated chimney to go through the roof and up.
 
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Alden Banniettis wrote: I  have seen advice given on various forms that says to burn a hot fire in the morning in order to burn out any creosote that might have formed in the flue/chimney.



I think they may have been a little confused as to what was happening. From my experience, I have noticed a quick hot fire in a cold system kind of shocks the system, and as the stovepipe/liner expands from the heat, the deposits break loose and fall free.
 
Douglas Alpenstock
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Jordan Holland wrote:From my experience, I have noticed a quick hot fire in a cold system kind of shocks the system, and as the stovepipe/liner expands from the heat, the deposits break loose and fall free.


Hm! That's interesting.
 
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