rocket mass heater: duct burns?

I just got the following post out at http://www.youtube.com/watch?v=hmYaIrHRMLM

Galvanized ducting is not rated for wood stove pipe. Plated pipe will give off toxic fumes when heated. It is the wrong product to use, even though everybody thinks it works great is is creating poison gas that is very unhealthy.
Ask any wood stove expert. use black pipe or blued pipe or stainless for high gas ducting not plated.

I think this is an excellent question. 

I suppose duct is good for temps like 200 or 300 degrees.  But it does seem that inside of the combustion chamber it will get way hotter.  Do we need something better for the combustion chamber?

Also, should we use something better for the first six feet or so of the mass?

why? the galv is gone in the test fire. don't breathe the smoke for a few min.

I tend to burn off the pipe at any rate cause i don't want to endanger folks in the work shops. Before someone puffs up like an adder to give me a good bite,

lets get this straight galve burns off at low temps, yes its toxic, yes you are knowingly polluting to make a system that will pollute less in its lifetime.

dont drive for two days and pass up one soda and you have paid your toxic debt for the stove.

the diffrence is you know that, its not sent to some re manufacturing place where its burned off in bulk along with several thousand pounds of other mixed metal coated with god knows what.

reality Galv causes whats known as metal flu if you get too much; but its zinc we are talking about here not cadmium.
lead is no longer part of the manufacturing process for galvanized pipe.

my response would be for the poster to read up on what the risk actually is.

paul wheaton wrote:
I just got the following post out at http://www.youtube.com/watch?v=hmYaIrHRMLM

Quote

Galvanized ducting is not rated for wood stove pipe. Plated pipe will give off toxic fumes when heated. It is the wrong product to use, even though everybody thinks it works great is is creating poison gas that is very unhealthy.
Ask any wood stove expert. use black pipe or blued pipe or stainless for high gas ducting not plated.


I think this is an excellent question. 

I suppose duct is good for temps like 200 or 300 degrees.  But it does seem that inside of the combustion chamber it will get way hotter.  Do we need something better for the combustion chamber?

Also, should we use something better for the first six feet or so of the mass?

When you ask any woodstove person about it, they'll definitely agree with your commentator.  It's a very dangerous choice for stovepipe in a conventional woodstove.  In addition to the high temperatures offgassing metal vapors, you also have the high risk of structural failure from over-heated thin metal, and then your fire is gushing out the bent/broken stovepipe into your home.

Wood stove experts tend to avoid that wherever possible.

But for some reason, woodstove and appliance owners tend to be nonchalant about a catastrophic failure of their cheap 'stovepipe', but easily worried by invisible toxic gas.  Go figure.

Rocket mass heaters are a slightly different animal, because we have a greater range of temperatures.  The heat riser gets hotter than wood-stove-pipes, while the thermal mass is better protected and cooler than most wood-stove-pipes, and the exhaust is substantially cooler but exposed.

We do prefer 'something better' for the heat riser and first 6-10 feet of thermal exchange when available.  We also like to use something nice on any exposed pipe in the room, especially if it's close to the heat.

We've done galvanized heat risers before; they're not our top choice.  Generally too thin, and once the galvanized burns off, the steel underneath will crisp like overcooked bacon (6-18 months).   So this is a good area to use something more durable, or create your own insulative ceramic materials.  Whether or not you care about exterior offgas, which you probably should in a populated area.

In the earthen masonry of the thermal mass, I think any vaporized metal is re-condensing within an inch or two on the dense layers of absorbant clay.  So the only real indoor vapor exposure would be from exposed pipe like cleanout end-caps or the exit pipe. 

You might get some outdoor vapor if there's galvanized on the first, say, 10 feet of ducting, or wherever the temperature is high enough to vaporize the particular galvanization metals.

....

My father-in-law was a welder on galvanized ships back when there was a lot more God-knows-what in the galvanic dip.  Whether or not they knew better, they sent guys into enclosed spaces to melt and vaporize the stuff.  He's paying the price now with chronic pain and other symptoms.  But he did a lot of work before he retired, and it took him years to build up those levels of metal poisoning.

The level of exposure matters as much or more than the material itself.
Like any metal vapor, or for that matter masonry dust, it's a hazard that increases with concentration and poor situation management.  Mostly, don't breath it, and don't release it faster than it can be absorbed nearby. 

Rain and sea-spray clean that stuff out of the air on a regular basis.  The deep ocean has a great capacity to absorb small concentrations of minerals, and put them to use.  Not infinite, of course, but awful big.

Whether it's adding to a local pollution problem depends on your locality, population density, and what the local mineral concentrations are like.  Many of these metals are trace nutrients at one level, and toxins at a higher dose.  Chromium, for example, is on the list of things we need in micro-amounts. Zinc they even put in losenges.  (Doesn't make it safe to breathe, but worth noting).

It would really help to know the particulars.  Most people involved don't really have a way to analyze their salvaged stovepipe, or enough experience to tell newer from older if it's in good shape, even if they happen to know where to find local air and soil data.

My sense is that the main danger in mis-use of galvanized is being stuck in a small space with chronic high levels of airborne toxins.  This is easy to happen indoors; and can happen outdoors in areas with heavy industry or high populations of DIY-galvie-burners.   If you can avoid these situations, so much the better.

But I do like to play devil's-advocate when I hear someone condemning something 'toxic'.  There's not much we use every day, that doesn't produce toxic clouds somewhere in its history.  Yet we often over-react to news of any particular toxin - especially if we didn't already know about it. 

Outdoor respiratory dangers are reported
- in mining towns with coal (or mineral) dust in the air;
- in textile towns with small fibers of fabric blowing on the wind;
- in deserts with silica dust;
- during/after volcanic eruptions, forest fires, or field burning;
- in developed cities from heavy automobile traffic and industry;
- in under-developed towns that cook and heat with small fires;
- and in the pastoral Willamette Valley in any of its 17 "nasty pollen" seasons. 
(This has been true since ancient times; there are a number of native remedies for "sore eyes" from smoke and/or pollen.)
Asthma seems to be on the rise, and it's not entirely clear why, or even if it means anything.

In other words, breathing is never 100% safe. 
But it's better than the alternative.

If you can afford a little more time and energy to build your heat-riser from something durable and non-toxic, I'm all for it.  But it's your choice.

Erica Wisner wrote:[
We've done galvanized heat risers before; they're not our top choice.  Generally too thin, and once the galvanized burns off, the steel underneath will crisp like overcooked bacon (6-18 months).   So this is a good area to use something more durable, or create your own insulative ceramic materials. 

For metal pipe, what would the recommended 'something more durable' for a heat riser be?

I am working on a Rocket Mass Forge. http://mike.creuzer.com/topic/builds/his/rmhf (or more specifically http://mike.creuzer.com/2011/10/rocket-mass-forge.html ) This would start with the heat riser, as I need an open space under it for the forge fire. If I am going to do woodworking in the garage, I can lay in a quick brick burn tunnel for the day. The whole thing is 'disposable', getting tore apart in the spring. The heat riser just needs to hold together for 6 months. However, if I can get something that will last several years for not much more money than the galvanized, I'd like to go that route.

I am using the lid of the barrel with two 6" holes, and setting the barrel upside down over the top of it. As there isn't any support at the front due to the forge fire being located here, I can't use a masonry heat riser, the weight would tip the hole thing over. So, it's 2 pieces of duct pipe of some sort with ash & perlite insulation. I was going to get more 6" galvanized as it's in a drafty garage, and the burning off of the duct happens inside the barrel, so the poisons gets vented outside anyhow. But, I am in a tightly packed residential area, and am not keen on poisoning anybody.

I had built a paint can pocket rocket using 3 inch double gas water heater pipe and 'crisped' the inner pipe within a half dozen burns. Crisped it 1/3 the way up the pipe! Photo can be found on http://mike.creuzer.com/2011/05/twitter-updates-for-2011-05-02.html

Is the 24 gauge black pipe good enough? Does the stainless last any longer? I'd think the black pipe would be a good compromise between safety, durability, and cost.

Mike Creuzer wrote:

Erica Wisner wrote:[
We've done galvanized heat risers before; they're not our top choice.  Generally too thin, and once the galvanized burns off, the steel underneath will crisp like overcooked bacon (6-18 months).   So this is a good area to use something more durable, or create your own insulative ceramic materials. 

For metal pipe, what would the recommended 'something more durable' for a heat riser be?

I am working on a Rocket Mass Forge. http://mike.creuzer.com/topic/builds/his/rmhf (or more specifically http://mike.creuzer.com/2011/10/rocket-mass-forge.html ) This would start with the heat riser, as I need an open space under it for the forge fire. If I am going to do woodworking in the garage, I can lay in a quick brick burn tunnel for the day. The whole thing is 'disposable', getting tore apart in the spring. The heat riser just needs to hold together for 6 months. However, if I can get something that will last several years for not much more money than the galvanized, I'd like to go that route.

I am using the lid of the barrel with two 6" holes, and setting the barrel upside down over the top of it. As there isn't any support at the front due to the forge fire being located here, I can't use a masonry heat riser, the weight would tip the hole thing over. So, it's 2 pieces of duct pipe of some sort with ash & perlite insulation. I was going to get more 6" galvanized as it's in a drafty garage, and the burning off of the duct happens inside the barrel, so the poisons gets vented outside anyhow. But, I am in a tightly packed residential area, and am not keen on poisoning anybody.

I had built a paint can pocket rocket using 3 inch double gas water heater pipe and 'crisped' the inner pipe within a half dozen burns. Crisped it 1/3 the way up the pipe! Photo can be found on http://mike.creuzer.com/2011/05/twitter-updates-for-2011-05-02.html

Is the 24 gauge black pipe good enough? Does the stainless last any longer? I'd think the black pipe would be a good compromise between safety, durability, and cost.

I simply don't recommend metal pipe in the heat riser. Or anywhere in the burn area.
Clean fire starts at 1200 F. Steel starts glowing around 900, and hits working temperatures (cherry red, where it starts to get soft enough for permanent deformation) around 1300.
A consistently clean-burning, well-insulated rocket mass heater can routinely hit 1800 to 2000 F, and we have some anecdotal evidence that super-insulated versions or stoves running rich fuels can get much hotter. E.g. forge-welding temperatures (2900 F). If it can transform metal, metal won't last in that environment.

We pretty much use brick - clay brick, either firebrick if we can get it, or reclaimed, older clay brick. We have done some prototypes with ceramic refractory materials, but these tend to cost more, are harder to replace if damaged, and don't hold up to abrasion as well as the brick.

Anything metal in the heat riser should be regarded as temporary.

Yours,
Erica W

Hi Erica,

You mentioned the temperatures obtained in a rocket stove. Could you be more specific please as to which part of the stove these temperatures relate to? For example, it gets to be up to 2000 Farenheit, but where? In the heat riser or within the barrel just as the gases leave the heat riser?

I appreciate clarification on this as I plan to heat water with titanium piping and am weighing whether or not to place the pipes within or outside of the 55 gallon drum..

Regards,
Karl

Erica Wisner wrote:

I simply don't recommend metal pipe in the heat riser. Or anywhere in the burn area.
Clean fire starts at 1200 F. Steel starts glowing around 900, and hits working temperatures (cherry red, where it starts to get soft enough for permanent deformation) around 1300.
A consistently clean-burning, well-insulated rocket mass heater can routinely hit 1800 to 2000 F, and we have some anecdotal evidence that super-insulated versions or stoves running rich fuels can get much hotter. E.g. forge-welding temperatures (2900 F). If it can transform metal, metal won't last in that environment.

We pretty much use brick - clay brick, either firebrick if we can get it, or reclaimed, older clay brick. We have done some prototypes with ceramic refractory materials, but these tend to cost more, are harder to replace if damaged, and don't hold up to abrasion as well as the brick.

Anything metal in the heat riser should be regarded as temporary.

Yours,
Erica W

I have been searching for this information for several weeks. We will be starting to build our house in the Spring and would like to install our RMH as we go. We would like to assume we will live in this house for the next 30 years and want the RMH to last also. Is this reasonable for a RMH with a brick riser?

We have "THE BOOK" along with many of the others mentioned here. Erica, will the plans for the Bonnie 8" heater adapt ok for a brick riser?

I will be back with many questions but we don't plan on experimenting, just building to plan.

Linda

Build the core out of refractory material, would it be brick, splits, clay flues with chamotte, or else. Don't use metal in there, metal is doomed.

When i talk about the "core" it's the J tube; feed tube, burn tunel and heat riser.

Satamax Antone wrote:Build the core out of refractory material, would it be brick, splits, clay flues with chamotte, or else. Don't use metal in there, metal is doomed.

When i talk about the "core" it's the J tube; feed tube, burn tunel and heat riser.

Thanks for you input.