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rocket stove pipe life?  RSS feed

 
Steve Nicolini
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Has anyone on this sight built a rocket stove in their own home?  I have a question about the metal pipe.  How often do you have to replace it, if at all?
 
Leah Sattler
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I wonder the same thing!! anyone?? we use an  old metal stock tank for a burn barrel and used to use a 55 gal drum. they don't last forever, but they also aren't protected from the weather at all. I suspect that the burning damages it quite a bit  over time, almost as much as the weather, and wonder how accelerated that is in the intense heat of a rocket stove.
 
Nicholas Covey
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My experience with the burn barrels, is that getting wet AND hot breaks down the steel over time. Now, take a cast iron pot and shine it up when you're done, and hang it up... it could last for centuries. Now, take it out and sit it in the rain after you're done cooking, but while it's still hot, and it will be pitted in no time.

Now, I'm not so sure that the barrel would wear out per se, but the question asked was about the stove pipe itself. My thought is that there are a couple of factors involved...

First, standard stove pipe is relatively mild steel, not high quality by ANY means, and heat is going to break down the alloys eventually. Now, from what I can tell, most of the heat goes to the barrel, and what goes through the stovepipe seems to be residual heat. Also, unlike pipe  that is open to the room, the high heat isn't bleeding off into the open air, and is instead soaking into a thermal mass, which in this case acts something like a heat sink. Therefore, that SHOULD keep the pipe cooler, allowing for longer life in the buried stovepipe.

Of course, that's all based on assumptions and you know what happens when you assume .
 
                    
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you can get stainless steel stove pipe. that is my biggest thing about the rocket stove is the flue gasses, may be fine for a greenhouse or shop but living space.!
 
paul wheaton
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Hmmmm ....  maybe some pipes are hotter than others. 

What about stove pipe?  It's gonna be able to cope better, isn't it? 

I kinda wonder about the difference between what we built (quick and easy) and what might be the next step up.  I wonder about something where the combustion chamber is square.  It seems like a square combustion chamber would be better than a round combustion chamber.  Plus, I would think that something that has contiguous metal from the fire box up to through the combustion chamber would be better.  So maybe taking

As for rusting ....  Aren't most wood stoves made from cast iron?

 
Steve Nicolini
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Will stove pipes bend the way those rocket stove pipes do?  I think it would cope better, but would it bend like the metal pipes do? 

My concern is not with moisture, though now I wonder: do people cook on the barrel of their rocket stoves?   
 
paul wheaton
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Well, the big one we fiddled with in "myrtle" would get hot enough to almost boil water

That particular style of rocket stove is for heating a room - not for cooking.  So the heat tends to be spread out over a large surface.
 
Erica Wisner
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Steve Nicolini wrote:
Has anyone on this sight built a rocket stove in their own home?  I have a question about the metal pipe.  How often do you have to replace it, if at all?


We have one in our living room, at least until the inspector comes on Thursday to decide about permitting it.

Here's a longish response to several points under discussion:

We don't have flue gas in our house.  That's kinda the whole point of the ducting and outside exhaust (we did a commercial stovepipe exhaust, because of the permitting).   There are some other recommendations in the building code about ventilation of rooms with solid fuel-burning appliances.  One builder added a 4" duct to bring outside air in for his stove, and cobbed it alongside the stove core to warm up the air slightly before releasing it right near the air intake for the stove. 


The oldest rocket mass heaters are Ianto's; the one in the Myrtle is about 10 years old and has only been taken apart for cleaning once.  (To clear ash from the heat riser lip and manifold.)  The interior pipes are still working fine, though one exterior section has rusted appreciably where rainwater/condensation collects on the bottom elbow.   

The metal pipe:
In the middle of the cob mass, the pipe is basically a form.  Theoretically, the sealed cob and plaster could channel the flue gas even if the pipes rusted out.  (This is one reason to carefully slip-coat the pipes, and wrap them in thermal cob before filling in with rubble.  The other is, thorough sheathing without gaps contributes to the cob's strength once dried, making the pipe like an arched vault.  Don't stand on it while the cob is wet, though, or you'll have a squashed duct.)
 
If you have enough moisture to make the pipes rust, you may also have a problem with the cob.  Like most plasters, cob needs to stay dry.   

In the "heat riser" section, people have definitely burned out pipes.  We used a stovepipe for the class (instead of mild steel ducting) but even so, one over-firing could seriously warp this pipe.  We've seen warping on triple-walled metalbestos heat risers as well.

For permanent installation, building an insulated heat-riser with firebrick or refractory ceramic foam is a great option.  Cutting brick is time consuming for a 3-day workshop, though.   You can create your own ceramic foam from clay and sawdust, if you don't mind the smoke while the sawdust burns out.  A cage of contractors' cloth on the outside of the heat riser (to support insulation) is not  exposed to the heat extremes inside, and holds up OK.

The barrel: ideally, it's the thickest, soundest metal drum you can easily get your hands on (absolutely no holes, minimal if any rust).  Ernie occasionally oils ours, like you would a cast-iron cook pan. 

The inside of the stove doesn't rust as fast as you might think because it's a low-oxygen environment (the O2 is used by the more reactive combustibles).  But condensation and rainwater are issues, especially near the outlet/exterior.  Design good drainage into your system if you have the option.

Like any woodstove, (especially for clean-burning ones), there's some basic maintenance that needs to be done periodically. 

You'd want to examine and clean out your chimney/ducting, about once a year ideally.  At least every 5 years.  Or whenever you see a change in performance that could indicate something wrong (e.g. a clog or leak).

If your barrel is outdoors getting rained on, yes, it will rust in short order.  So would any metal woodstove.  The standard method to avoid this problem is a roof.

Our friends at TLC farm have recently enlarged the roof for their outdoor kitchen, which contains a rocket stove bench as well as assorted earthen cookstoves and ovens.  That stove is only a couple of years old, but is holding up well.  Biggest issues:  Foundation was haphazard, so there were some major cracks.  www.tryonfarm.org
 
                      
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well as all metals go, breakdown depends on the concentration of acid in the water, and how long it is exposed to extream heat and cool air.  cooling and heating the metal will temper it, eithemaking it softer or stronger, but either way, allowing oxygen to corrad it. (oxygen is a liquid, and it is corrosive to metals) the best way i can tink of making a long lasting rocket stove is fire resistand bricks, and fire mortar. with ashas an isulator. will last 4ever. only problem is it is heavy hardto move
 
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