Wood stove biochar... a different approach?

Every few months I see a post about putting a container inside a woodburner to make biochar. I've been mulling for a while a different strategy. What if we just had a tightly sealed metal container next to the stove, and over the course of a few days just shovelled out a few loads of embers from the fire? We regularly have a thick bed of embers built up, at the point where it is time to put more logs on. The gasses have essentially totally burned off, so there is essentially no smoke produced

Seems like this would circumvent the obvious issues of using a container in the firebox itself - the container would degrade over time, and would obstruct the ability to load fuel normally etc...

Any thoughts on this?

Michael Cox wrote:Every few months I see a post about putting a container inside a woodburner to make biochar. I've been mulling for a while a different strategy. What if we just had a tightly sealed metal container next to the stove, and over the course of a few days just shovelled out a few loads of embers from the fire? We regularly have a thick bed of embers built up, at the point where it is time to put more logs on. The gasses have essentially totally burned off, so there is essentially no smoke produced

Seems like this would circumvent the obvious issues of using a container in the firebox itself - the container would degrade over time, and would obstruct the ability to load fuel normally etc...

Any thoughts on this?

I have saved charcoal from camp fires that way.  I can't see any reason it wouldn't work.  I would be very careful where I set the metal container down :)  Maybe on a brick or something.  It wouldn't need babysitting because you could just take some coals out whenever you felt like it.  It sounds like a great way to make small amounts.

Yes Michael, this is exactly what I did for several years and it worked out just fine for my needs.

Keep a bucket of water next to your stove and just dump the hot coals into the water to cool them. This also fractures the charcoal creating more surface area.

The tightly sealed container would concern me. I’ve made about 10gal of char for inoculation in my compost in the past month with an old cast iron Dutch oven. It’s heavier than the ideal to remove from the wood stove at 450f, but it naturally vents gasses to be fully combusted while heating the house. It also is thermal mass for heating the house after combustion and it seems to produce excellent char (makes that chrystalline crackling sound) when I get the stove to 600f, at which point I let it cool along with the stove, and the residual heat keeps the house warm for hours. It’s obviously not efficient for anything largescale, but it takes about 10min of loading and unloading to harvest 1gal of char. Good luck with your experiments, I look forward to improving my setup based on your insights.

Seems as if it would work fine. Isn't this a variation on how old-timey bed warmers worked? Pull a few coals from the fire and put into the warmer and close it up?
Instead of summertime burns outdoors, you'd be doing the same function stacking (biochar while space heating) just like the micro-retort folks are...
I think the retort suits a different function stack for them... of turning sawdust, wood shavings, and off-cuts, from a woodworking hobby, into char. Which seems would be a hassle to load/burn in the stove as loose material, without the retort?

As I thought it through more, it shouldn’t build up too much pressure and indoor smoke could be avoided.

Kenneth Elwell wrote:
I think the retort suits a different function stack for them... of turning sawdust, wood shavings, and off-cuts, from a woodworking hobby, into char. Which seems would be a hassle to load/burn in the stove as loose material, without the retort?

Retorts can also be used to char things other than wood. In my mind, that's the biggest advantage they have.

I don't have a lot of wood available, so most of my char is made from crop waste, which doesn't burn hot enough to char itself.

If you're making char entirely from wood, you have a lot more options.

Michael Cox wrote:Every few months I see a post about putting a container inside a woodburner to make biochar. I've been mulling for a while a different strategy. What if we just had a tightly sealed metal container next to the stove, and over the course of a few days just shovelled out a few loads of embers from the fire? We regularly have a thick bed of embers built up, at the point where it is time to put more logs on. The gasses have essentially totally burned off, so there is essentially no smoke produced

Seems like this would circumvent the obvious issues of using a container in the firebox itself - the container would degrade over time, and would obstruct the ability to load fuel normally etc...

Any thoughts on this?

I used to heat my home with wood and use the char to run a tractor. Here is a video I made awhile ago now on making charcoal in the stove. I tried retorts but they wear out due to the stress of the fire. I was grinding and sieving so the ash was no problem. Hope this helps some.
Cheers, David