Sawdust stove

Hello everybody, I am new on this forum and also share interest in energy alternatives. I am now building a sawdust mass heater and out of curiosity,I would like to know if using sawdust from cabinet maker shop ,which cut lots of melamine and agglomerate materials would be bad for the environment since they are full of chemicals? Would the stove burn hot enough to burn them ? Or is it better to stick with pure organic material ?Sorry if the question was raised before but I did go true the postings yet. Thank you for sharing your experience.
Jacq.

Hello Jacques, welcome to Permies!

I have experimented with combustion of synthetic board materials to see the results.
I've burned the different engineered wood with not so satisfying results. Particle board tends to burn ok, medium density fiberboard burns less well, and the laminates I'm scared to try.

I've noticed a chemical smell when burned. The engineered woods don't tend to burn as hot. The engineered woods do burn to ash, but take more heat and sometimes need to be mixed with good wood.

If the rocket mass heater is hot enough the nitrogen in the melamine will become nitrogen dioxide (the brown gas that smogs cities from vehicle exhaust). If the rocket mass heater is not hot enough the thermal decomposition products are ammonia, nitrous oxide, cyanide, cyanamide and other permutations of the melamine molecule. Using my organic chemistry background, some of the melamine permutations resemble pesticides.

I believe many engineered woods also have fire retardants (borates and phosphates) added to inhibit their combustion.

Having done my experiments with them, I would not recommend burning them.

Thank you Brett, this is clear enough answer for me.I will stick with good wood and avoid other composites and problems .
That brings me to another question since I am in the process of building my stove. Once the stove as reached it's ideal burning temperature, how do we control the heat output without choking you fire and compromising the efficiency of the combustion and, so the stove doesn't start to smoking again? Is there a ratio air intake v/s output ?

You have to control the fuel. A rocket stove is usually fuel limited by the nature of the feed tube.

I am really curious about your design, as I have been looking (unsuccessfully) for a way to burn sawdust cleanly.

I suspect my experience is fairly common. I have heard others make similar observations, at any rate.

The fire runs hot and at full speed, for the most part, and then it burns out, and shortly thereafter you close up the feed tube opening.

You listen to the stove "rocketing" and when you no longer hear it rocketing, you know it is time to rearrange the wood, and wiggle the sticks around to get it going at a "roar" again. You may or may not add more wood at this time. And at all times during the burn, you periodically move the covering fire brick over the feed tube opening to keep the bricks snuggled up to the wood, so as to reduce the size of the air gap.

If the wood burns down substantially, and you have not snugged up the brick, reducing the air gap, it may begin to smoke-back into the room. Also if wood snags and fails to fall down into the ashes, it may encourage smoke-back, or start to go out; this difficulty is reduced by feeding the sticks in big-end first, so that the smaller diameter end is sticking up. That way the bigger part burns first, and the stick tend to fall onto the coals on their own, because there is slightly more room as they all burn. However, odd pieces of bark or little stubs of old branches can still get caught up, and then you have to adjust the stick manually.

When my last stick "falls" I rake the coals into a pile, and place that small piece of wood on top of them. I then close the air gap to something like 1/2-inch or maybe as much as 1-inch. When that appears to burn all the way down, and there are only coals remaining, and not any wood pieces to burn, and no flames, I reduce that gap to something like 1/4- to 1/2-inch. Then I leave it that way until I think to check it again, usually on the order of 30- to 60-minutes. I rake the coals, seeing what I see. If the coals appear dead, I will reduce that gap almost completely.

If I am still up an hour or more later, I may check them again to verify it is only ash, and no little pieces of coal in there; if so I may close the feed tube opening as well as I can. In my case, that means putting laying down a piece of aluminum foil larger than the opening, on top of that, a couple pieces of ceramic tile I have, and on top of that I place my fire brick that I use to control the air gap while it is burning.

I have not made a P-channel, but that is something else one may wish to investigate. It gets good reviews by most who have tried it. Peterberg came up with the idea (hence, Peter-Channel, or P-Channel) That is a piece of metal that is shaped like a fat T, that is inserted into the feed tube opening, in such a way that it maintains a small gap between the wood, and the edge of the feed tube opening that is nearest the opening to the burn chamber. There are extensive forum discussions of this over at Donkey's forum (go to http://donkey32.proboards.com/#category-1 and try searching for Peter-Channel and P-Channel; or maybe someone here can post direct links). This was also discussed in the the appendix of "the Book" by Evans, at least in the latest edition (I don't know which edition the P-Channel first appeared).

Jacques Lapointe wrote:Hello everybody, I am new on this forum and also share interest in energy alternatives. I am now building a sawdust mass heater and out of curiosity,I would like to know if using sawdust from cabinet maker shop ,which cut lots of melamine and agglomerate materials would be bad for the environment since they are full of chemicals? Would the stove burn hot enough to burn them ? Or is it better to stick with pure organic material ?Sorry if the question was raised before but I did go true the postings yet. Thank you for sharing your experience. Jacq.

Jacques L.: The link I provide below is to a Forum thread that I found by using our [ Search } function, and was just one of several Forum Threads on this topic

ThisThread has a further link to a U-tube video of the only type of working Sawdust stove with a Rocket-like action though it will not burn ether as hot or as clean
if you have lots of sawdust this is a very simple system to make even w/out plans


https://permies.com/t/5483/wood-burning-stoves/Sawdust-fired-Rocket-Mass-Heater


From some of the otherwise great comments posted by our Fellow Members, I do not think this link was what they were thinking of ! For the Good of the Craft !

Big AL

The stove that I am working on is a typical double wall sawdust stove similar to the ones I saw on you tube but made out a metal pool filter thank. Quite cute. It was originally made as an ordinary wood stove that I am converting.And before I make a whole for the air intake,I was just wondering what size would be enough since the exit is 5 inches. Or maybe I can just control the ventilation by the opening I will use to light the combustion chamber, at the bottom of the stove. I don't particularly want to complicate the construction more than needed and keep it simple, safe and efficient.

Thanks everybody for your replies it is all interesting. Allen, this is the video I was referring to and brought me on this forum, thanks.I will send you guys some pics later on to show you where I am at with my construction. Anyway, I am sure that some questions will arise along the way, and I will take the time to visit the the topics and discussions on the forum, which I am sure to find some good answers. Catch you later.