Outdoor wood stoves

[django]

Pictures, Pictures, Pictures!!!!!!!
I don't know how one would begin to build one yourself. They're freaking HUGE. That ceramic insert alone would be hundreds of dollars. ( Unless you have connections.) Also, I believe they're doing some wild stuff with the draft to get those "aromatic hydrocarbons" to burn nearly completely. (catalytic stuff)Very high temps. Other outdoor burners are dinosaurs compared to this Garn stove. I'm not wild about starting a new fire every time, but that's the "only" way their system would work.

 

[bwalker]

Django, Your right. Current outdoor wood boiler designs are crude. What they need to do is incorporate some of the new woodburer tech into these outdoor units. Things like catalysts and gas reburners would be nice.

 

[Gopher]

Agree

django, I agree that from what I've seen and used, the Garn unit seems to have the most engineering and physics in mind. No matter what, it is better than paying Alliant for the natural gas every month!

Gopher

 

[django]

I don't know what you would do to really make an outdoor stove as we know them burn at high effeciencies like the Garn unless you do what Garn does, and that is heat huge amounts of water with ONE burn cycle. ALL THE FUEL AT ONE TIME(I'm not yelling, just want to make sure this point is made) This is absolutely the key to the whole thing. You could go to all the trouble of incorporating all that techy stuff, but unless you use All the fuel at once, when you stop your burn cycle, what is left in the stove smoulders and is therefore very inefficient and dirty. There is no way around this, unless you somehow say you are going to heat the water to a certain temp. and "bleed off" the remaining fuel to somewhere besides the water, and that would be even more wasteful than letting it smoulder until the next burn cycle. So by their very nature, "standard" outdoor boilers, because the store energy in the water, AND the fuel, are very dirty combustors. Garn gets around this with a very simple principle. They don't STORE any energy in the fuel, they use it all. At one time.With this system ALL of the STORED energy is in that HUGE water tank. I apologize if I'm on my soapbox a little bit, but I did a lot of heavy thinking on mine before I made it and get a little carried away when I discuss the topic. The Garn is definitely cool. I'm glad somebody dared to be different.

 

[Bill G]

My ISP has been down the the better part of a week so I have missed some great discussion. One thing I do not understand is the Alliant energy in Iowa will pay the difference between the cost of a new 80 percent furnance and a high efficiency one. I put a 90 percent furnce in a rental because of that. In Illinois there are no rebates. I am wondering if there are any energy companies that will give assistance to people putting in wood burners. The concept is the same a reduction in energy demand thus lowering the need for more power plants. This allows them to use the same plants but charge a higher price per therm and KW. In the midwest we are experiencing another very mild winter. They are now claiming a shortage of gas and charging more. It is hard to believe their arrogance.

Bill

 

[Gopher]

Energy rebate?

Good question on the rebate for using wood. I am the contract arborist for a western WI electric co-op, so in the near future, I will talk to the director to see what and if there is anything they do. I didn't receive anything when I was a member there, and put in my wood furnace, but I didn't think to ask, either.

I think you may be on to something there.

Gopher

 

[django]

Garn Lit.

Got my Garn Brochure on saturday. YIKES. One the size needed to heat my house is $9500. Uninsulated, no shed. Takes over $500 just to treat the water for corrosion. Made from mild steel.
The thing weighs over 20000 pounds when it's full. By the time you get one delivered, insulated ,ia a building, run all your lines, pumps, etc....
you'll have a very substantial investment. I saw nothing in the literature pertaining to a warranty. Nothing. "Corrosion management is the sole responsibility of the owner" is all it says.
Nice stove. Grossly overpriced.

 

[bwalker]

10K is a awful lot for a incomplete system. It would take you a very long time to pay back the amount it cost over a OWB with the amount of wood you would save. Also, no warranty on a mild stee system. I would be very leery of that.
Django, Remeber whe we talked about the heat transfer rates of various steels? I just found a chart that lists them. Some grades of stainess are really poor. What about titanium? Corrosion would not be a issue, but cost likely would. I wonder how Ti stacks up heat transfer wise.

 

[WRW]

Probably not very good heat transfer properties for titanium. It is used as a heat shield on some airplanes.

 

[Crofter]

Heat transfer

Difference in net heat transfer of stainless vs mild steel wont amount to anything because the lesser thickness used will cancell the conductivity factor. Forget about Titanium; it is many times more expensive than stainless and much more difficult to weld. You see it and columbium listed as a minor alloy in stainless steel to reduce grain boundary corrosion in weld zones. Back to the heat transfer. There is almost always a layer of ash and creosote "FUR" on the inside of a boiler and I would guess its R value is a lot greater than that of the metal. Net transfer is the average of the two resistances so the conductivity of the metal is maybe not as important as would appear. I would trade longevity over ADVERTISED efficiency I think.

Frank

 

[bwalker]

Crofter, Yes, you are probaly right about the creosote/ash limiting heat transfer, bu the differance between 1010 mild steel and 304 stainless is quit abit. Here are the figures. AISI 304 stainless 14.9 W/(m-K), AISI 1010 mild steel 63.9. I dont know how this corresponds with the steel used in furnaces, but it gives you a idea of what you are dealing with.

 

[django]

I agree with Crofter, ( man, I hate it when that happens) Titanium is a complete pain to weld, fab and machine. "Exotic" metals really are only good for "academic" type discussion. Neat, but impractical for many reasons. I would like to see the firebox on some "stainless" stoves after a few years, one to see how they "resist' corrosion, and two, since they are typically only 1/8" thick, and stainless is a "soft" metal compared to mild steel, how they take the abuse of having 30-40 lb. logs( and more) thrown into them. I know mine takes a pretty good beating. Frank makes a good point about the "coating" on the inside of the firebox also, creosote is a good insulator. And you WILL have this coating in any of these stoves. As to efficiency in general, they all pretty much stink. Anytime you see efficiencies bragged about, read the fine print, it's pretty comical.

Frank, Yes or no, When welding "stainless" steels, especially for a boiler type application, should the welds be annealed??
Django

 

[bwalker]

Titanium is a complete pain to weld, fab and machine

You got that right. I read a story once about a machine shop that had a cooling pump go down or some other malfunction while cutting a piece of Ti. The piece got so hot that it melted right through the mills table and through the concrete floor! Now thats hot.

 

[django]

http://www.woodheat.org/technology/obmanufacturer.htm

Found this on the web at a site that is very anti- outdoor woodstove. Posting it for what it is worth. Entertainment purposes only. The views expressed are not necessarily those of the poster.
Django

 

[Crofter]

Post weld annealing of Stainless

Django: Stainless welds of the 300 series nominal 18 8 have excellent ductility as welded so there is no gain in that respect (Cracking) If there are any transition welds from stainless to mild steel, annealing is definitely a no. With the 409 so called stainless which is not stainless, ductility is not as good so some preheat and post heat would give some benefit. Be careful to have no unercut or overlap on welds helps.

Ben: That figure seems high. Just from memory I though mild steel had 1.5 or 2 times the conductivity of stainless. The figure also is likely for the same thickness, but you would most likely only use stainless at about half the thickness of the carbon steel , so I think that would contribute less transfer resistance.

Frank

 

[Gopher]

Garn (or should I say "Darn") price

Django - thanks for getting a current brochure. My God, for something like 4K less I can have a decent unit with a better warranty. I don't care how good Garn is, if they are 60 to 70 % above the others, I won't buy it. That means by the time I got a pad poured, and everything hooked up, I'd have over $11,000 into it.

No way. I can get the whole thing done for about $7,000 and have a nice system using Heatmor, Central Boiler, etc.

I'll talk to you more after this summer to see if I can get going on another one (we may dump this house and make some good money, so I don't know if I am going to do it at this location).

Gopher

 

[django]

Yup, I agree. If you don't mind the smoke, and youv'e got plenty of wood, then you don't need that technology. Did you read the link I posted from woodheat.org? This guy supposedly is an "expert" on outdoor stoves. I don't think so. I could tell you all about some "magic stove" that is so much better than what is out there too.... Just don't ask any specific questions.

 

[tree_reaper]

http://www.freeheatmachine.com/Web Pages/models.html

 

[prez1520]

I just bought a new heatmor and I wondered if anyone could suggest an efficient system for loading heavy 4 foot logs.

 

[bwalker]

Cut them smaller?