Aircrete Rocket Stove Keeps The Batch Box So Warm It Can Burn Wet Green Wood

Thought this was a cool video. Darwin just put the plans up and you don't need to know how to weld to build it.

The stove looks interesting, I am not sure if I am getting this right but it seems Mr Honey do is selling digital plans to build his version of a rocket stove for $250.?

I dont think he has had it officially tested in any way or if it is in any way a better performer than Peters Batch  Box that has been extensively tested and the detailed plans are free?

Just asking for a friend?

If aircrete is really a suitable and durable material for the core of a batch box, I could see using it in a tested design like Peter's.

I am skeptical about wet/green wood being as good to burn as seasoned wood... yes, with a hot fire going, you can burn it, but would seasoned wood put in give the same heat, or more? Boiling water purely takes energy rather than giving anything. Pine pitch is not water and has heating value. Of course green wood will last longer, i.e. take longer to burn up due to having to evaporate all the water.

Fox James wrote:The stove looks interesting, I am not sure if I am getting this right but it seems Mr Honey do is selling digital plans to build his version of a rocket stove for $250.?

I dont think he has had it officially tested in any way or if it is in any way a better performer than Peters Batch  Box that has been extensively tested and the detailed plans are free?

I have to agree with Fox James,  and add, If  anyone on this "permies" group finds any of this to be true, Please do post....but in the mean time, I don't think the basic principals can't be done, but would love to be proven wrong.

Such as, I think he is saying
-his green wood burns as good or better than dry wood, humm
=his mass holds more heat for less weight than anyone elses
= his riser is better than anyone else's
- in others videos he has reported  2500-2700 degree's F   but can the  the rest of us get that? hummm.....
- 4 inch flue pipe, really?

There is always hope, always...

Burning wet wood comes at a cost. Part of the heat, whether that's from the wood itself or the other fuel and the combustion chamber around it, gets used to turn the water into steam. If the appliance has some way to recover part of that heat from the flue gases before they leave the system, then it's not a complete loss. But I have yet to see a RMH design incorporating a stack condenser (would love to see one if anyone has done this, though!).

So, my take on this is that it's interesting but you'd be better off burning dry wood. I'm also going to go out on limb and speculate on the durability of aircrete as a burn tunnel material: It will fail long before a firebrick or refractory one. Portland cement, with or without bubbles in it, is unsuitable for high temperature applications. We know this because we've seen the results. Are there any examples of this design in consistent operation over multiple years?

Until we get some longevity data I will continue to recommend that people stick with methods and materials that withstand the test of time. It's fun to tinker if that's what you want to do, but it's a different matter when someone decides to heat their living space with an unproven technology and it craps out in the middle of winter.

Phil Stevens wrote:Burning wet wood comes at a cost.

Until we get some longevity data I will continue to recommend that people stick with methods and materials that withstand the test of time. It's fun to tinker if that's what you want to do, but it's a different matter when someone decides to heat their living space with an unproven technology and it craps out in the middle of winter.

Exactly!  Well said.

Glenn Herbert wrote:If aircrete is really a suitable and durable material for the core of a batch box, I could see using it in a tested design like Peter's.

For some years, during week-long workshops, I was making a habit of building a batch box rocket core mock-up out of air entrained concrete blocks, a.k.a. aircrete. The things worked without a hithch, were great as a demonstration tool. But this aircrete is in essence just foamed-up portland cement which can withstand no more than 520ºC. So in 3 or 4 hefty burns the aircrete was spalling, shrinking, cracking and falling apart.

This guy is very enthousiastic about his find, that's for sure. And burning green wood is a necessity in order to keep his aircrete core within certain temperature boundaries. Using dry wood would mean failure within a couple of days since temperatures in a batchrocket core is easily twice as high as the aircrete is capable to withstand.

I am not sure how the stove is built, he talks about using refractory cement so maybe the core is lined with castable refractory and surrounded with aircrete or perhaps the aircrete is made with high temp cement?
Also the other video recently posted suggest  one of these stoves has been running for several  years.
Hopefully mr Honey do, will  be along soon….

Fox James wrote:I am not sure how the stove is built, he talks about using refractory cement so maybe the core is lined with castable refractory and surrounded with aircrete or perhaps the aircrete is made with high temp cement?
Also the other video recently posted suggest  one of these stoves has been running for several  years.
Hopefully mr Honey do, will  be along soon….

That's how I understood it. The important parts are a high-temp castable refractory and the foam-crete insulates around it. I imagine the foam-crete would do well to hold stuff together as well.

The refractory is going to heat up to RMH core temperatures and surely the aircrete will start to degrade from the part that is in contact with the lining. We normally surround a burn tunnel with insulative material that can withstand lots of heat: superwool, perlite, pumice, etc.

I've done a postmortem of a failed combustion chamber and for the first two seasons it seemed great...I'm still not sold on the concept over the long haul until I see a teardown of one that's been running for at least a couple of years in daily service.

Scott Weinberg wrote:

Fox James wrote:The stove looks interesting, I am not sure if I am getting this right but it seems Mr Honey do is selling digital plans to build his version of a rocket stove for $250.?

I dont think he has had it officially tested in any way or if it is in any way a better performer than Peters Batch  Box that has been extensively tested and the detailed plans are free?

I have to agree with Fox James,  and add, If  anyone on this "permies" group finds any of this to be true, Please do post....but in the mean time, I don't think the basic principals can't be done, but would love to be proven wrong.

Such as, I think he is saying
-his green wood burns as good or better than dry wood, humm
=his mass holds more heat for less weight than anyone elses
= his riser is better than anyone else's
- in others videos he has reported  2500-2700 degree's F   but can the  the rest of us get that? hummm.....
- 4 inch flue pipe, really?

There is always hope, always...

He isn't saying that it burns better with green wood. He is just playing with different fuels to see if it causes a problem to burn wet wood. So far it will burn wet wood just fine and still no smoke or creosote but the wet wood cools the stove down quite a bit. It runs best with a mix of dry and wet and also if the wet wood is split instead of whole.

Phil Stevens wrote:The refractory is going to heat up to RMH core temperatures and surely the aircrete will start to degrade from the part that is in contact with the lining. We normally surround a burn tunnel with insulative material that can withstand lots of heat: superwool, perlite, pumice, etc.

I've done a postmortem of a failed combustion chamber and for the first two seasons it seemed great...I'm still not sold on the concept over the long haul until I see a teardown of one that's been running for at least a couple of years in daily service.

Yes, our first attempt melted the steel...within a few months. This one is a refractory mix batch box. Then the layer of aircrete outside that and then the sheet metal outer shell. This mix is alumina cement used by NASA to make their outer tiles for the space shuttle. Insulating the outside of the batchbox with aircrete keeps the back of the batch box so hot that it is a complete combust.

So you're saying that the aircrete is an alumina cement?

I think the refractory mix is an alumina cement.

Julianne Siddoway wrote:

He isn't saying that it burns better with green wood. He is just playing with different fuels to see if it causes a problem to burn wet wood. So far it will burn wet wood just fine and still no smoke or creosote but the wet wood cools the stove down quite a bit. It runs best with a mix of dry and wet and also if the wet wood is split instead of whole.

Sorry my mistake,  saying as good, not better.