Solomon Parker

Jeremy VanGelder wrote:You have knocked over that core.


Was it a five minute riser on top of a ceramic fiberboard core?

The amazing part is that it's melted and still works. I mean, I had to cram a bunch of fire bricks and some chunks of CFB in it to constrict it down, but it's still working today.

No, it wasn't a five minute riser, it was a ceramic fiber riser sleeve, 2" wall thickness, 8" (nominal 7.5" actual) internal diameter, two 24" sections stacked on the top of the core.

I do wonder what happens when a 5MR melts down.

If I were to do it again, I would line the bottom and sides, at least with fire brick. This burn tunnel of the core was 3" too tall, which was fine on lower BTU fuel, and when it was full of ash, but the ceramic fiber was rapidly abraded inside the burn tunnel during ash removal, most of which was by shop-vac. I would have reduced that height to a consistent 8" nominal cross section, and lined any parts that could be touched with brick. I would also have used a brick feed chute, rather than steel. As predicted, it warped badly and had to be ground on and bent back into place periodically. However, it did work. I would also capture the entire core in masonry rather than let the manifold section be open, just so the masonry couldn't warp out of place.

Other than the issues above, I was very happy with this system, and it performed admirably. It is very easy to start, being a very wide open system. It was a great first system. Good for learning and also heating. No smokeback issues, never any issue with draft.

Oh, I also added a "Magic Heat Reclaimer" to extract more heat, which it does, though I want to put a bigger blower on it to give it more power.

UPDATE:

Hey all, I haven't posted in a while, but I'm still around.

Just wanted to post an update on how the Aslan Core is performing in the midst of our second full winter.

The short answer is, too well.

So, what's been happening is I cleaned up an old weed growing operation where they used 5" 2x4 and 2x3 blocks as spacers for the racks to dry the weed. They gave me about a cord of these, maybe more, and me, never being one to turn down free firewood, (cured and pre-cut even), took it home and threw it in my wood shed and have been burning it this year.
Now we have switched back to mostly cord wood with smaller supplements of the blocks. I also added firebrick splits to the bottom of the burn chamber to tighten up the cross section and reduce the throttle, temps, and burn rate.

I do remove the screws before burning. I've collected about 5 pounds so far, good quality star drive 3 inch construction screws. It's fantastic because it was free.

The problem is, it burns way too fast and hot and since my thermocouple has been malfunctioning, I didn't catch it. So the inside of the core has been melting away, turning to glass and dripping down. All the ash (yes I mean all) has been getting sucked into the mass where it settles.

So here is the lower two foot section of riser. It is completely glassed. I'm not saying it can't be reused, I might still reuse it. It was only about 7.5" to begin with so now with the melting and added roughness, maybe it's 8" equivalent.


Here is the upper two foot section of riser, not glassed, but definitely overheated. Remember, this stuff was rated to 2300 and on my first test, I tested it to probably 2400F.



Here is the rear section of the burn tunnel and the manifold:

You can see booger colored chunks of melted riser glass around the edges.




Next is the view of down the bench. All of the ash was either being converted to clinker or sucked down into the bench. Previously, about half the ash was staying in the burn tunnel, about half in the manifold and just a little bit was ending up in the bench. This deposition that you see here is only from THIS WINTER'S burns. I cleaned all of this out before the heating season. The whole of last winter only deposited ~1 inch of ash in the bench.


This ash almost looks like volcanic ash more than wood ash. Volcanic ash is what happens when you take red hot rock and squeeze it out through a small orifice at a million billion pounds per square inch.
On the upside, heating has been great, we have heated almost exclusively with this stove. Pretty standard operation, once or twice a day burn for a couple hours, and it heats the whole house, with the help of some blowers and fans to move air around.


So, what to do.

I was already planning on replacing the J-Tube core with a batch box core this coming spring/summer. So I'm not worried about having destroyed the J. I have put a couple things in the system to slow down the gas flow and put a throttle on this thing. It seems to have worked, so I hope that holds together for the rest of the winter. If it doesn't, then I buy some more heater buddies and heat with propane until I can get the new stove rebuilt.

Given how it turned out, which you've seen in this thread, I'm thinking instead of just replacing the core, I'm going to tear down the whole thing and start from scratch and build a large masonry heater with a batchbox core. I want it to fit in the corner better since sitting on the bench never really worked. It would be much better for the floor space in the room and would look more conventional and presentable. This will give me the opportunity to make some adjustments using the experience I now have, to build a machine which is more serviceable, more durable, and easier to operate.

I'm going to do almost exactly what Peter (and friends) did in his "Mallorca" build, except scaled up to 8".

Hi Thomas

I have browsed your wares in the past, but I had forgotten. I appreciate your perspective and your replaceable riser idea is smart.

What you mention is one of my concerns. I know, the efficiency differences are low, but to my eye it seems there is a noticeable difference in efficiency and CO production between the OG Batch box and the DSR series.

Just a little more context, what I'm planning to build is almost exactly Peter's "Mallorca" build except scaled up to 8".



So that scales up to being about seven feet tall. I'm also going to double brick the bell/mass to provide extra thermal mass.

Would be awesome to have a bigger door to look at the fire. But I grew up doing much labor to bring in wood, so I am very interested in efficiency. Also like simplicity and durability.

I've been running a J tube for two years now, and now I'm ready to move up to more of a "Batch Box Masonry Heater" with a batch box firebox and a large masonry bell and bench. But which core?

Original batch: Very well attested, mature, but very tall, firebox on the floor, narrow firebox, secondary air to build and replace (building is not an issue, I am a competent welder, but replacing might get a little annoying. I like to fix things, but I also like them to stay fixed.)

DSR2: Less well attested, good height due to no riser, meaning the firebox can be off the floor, simpler construction using castables (if you can get them) and brick, but narrow firebox, secondary air to build and replace

DSR3: Wider firebox for good viewing window, no secondary air to worry about, and the most damnable aspect of all, precious little build guidance. I can't even make an informed choice, because I have very little information to get informed on. What are the sizing parameters? Build materials?

Carla Burke wrote:Thank you - sounds like it's working out well, for you. I'm still exploring ideas, and am very happy to learn as much as possible about all the different types of rmh.

That's very good. Remember to seek the views of the experts, read all the books and watch all the videos, and don't trust your own intuition too much until you've built your first one.

Carla Burke wrote:Solomon, this is GREAT!! Do you have any pics of the whole thing, at the current stage?

It really doesn't look any different now except that it has some black tiles sitting on top of it. We've been using it as is all winter, and have been pretty happy with it. I wish it had more mass so it was more efficient and held more heat, but other than that, it's been great. Been feeding it mostly free wood all winter.

I did recently remove the "P-channel" from the feed tube. As a result, it calmed down a bit, doesn't burn quite so hot or fast. The Testo results led me to believe there was an excess of air. I can't be sure, but I believe it is burning a bit more efficiently now, though slower, so we have to burn longer. But feed times have gone from 15-20 minutes to 30 minutes or better for a good load of dense wood.

Glenn Herbert wrote:If your wood rack is 4' x 4' with one layer of stove length wood, that would be 1/6th of a cord. Sounds much better for wood usage

Yes, we figured that out when Luke came with the Testo. 1/6 of a cord lasts us 7-10 days depending on weather. If we were burning oak or madrone only, it should be able to last 2 weeks or more. When I was a kid, we had a 100 year old wood stove that could easily consume 1/6 of a cord PER DAY!!! And even more on many occasions. Our wood box probably held 1/4 of a cord, and with less dense wood, it could go through that in a day, no problem, saying nothing of all the wet wood we burned because we would run out of wood in the middle of the winter and have to go cut more. I vowed I would never do that. Now I use so little wood that I never have to.

Update: Luke came and we ran the Testo for several hours, several different fuels, playing around with some experiments.

Conclusions:
The stove can be very efficient when run correctly, many times we were able to reach under 30 PPM CO for the main burn.

However, any extra air caused spikes in CO.

So I conclude that perhaps the original size feed tube was probably the right one. The bigger one burns hotter and faster, but not consistently.

When we tested, I had just done a full cleaning, so it had very little ash in it. I noted that it is much more volatile when ash free. Perhaps it needs some restriction in the chimney or somewhere which is not affected by ash accumulation.

The mass is definitely too small, which I knew from the beginning, but that's the space I had to fill. My exhaust temperature is most often in the 490-550F region, which means I'm leaving 250F worth of heat on the table. So I'm tentatively planning on adding a second tier to the mass, perhaps even including an oven. I had wanted to use the stove as a bench to sit on, but that may simply not be feasible, especially due to the shape of the bench and space.

Aside from those things, this stove works fantastically, it heats a poorly insulated two story 3800 sf house with an acceptable amount of wood. The ground floor, which we call the basement (we are just barely in the flood plain) is partially uninsulated and has an 18" uninsulated CMU foundation wall around the perimeter, and an uninsulated concrete floor. It is still very leaky and there is one wall which is totally uninsulated.

But, as I am who I am, I am always in pursuit of higher efficiency. I think I'm going to remove my P-channel, as the stove gets plenty of air, and I may reduce my feed tube size, and eventually I plan on converting to a batch box. More mass would be nice for maintaining a constant temperature as well, more constant heat output.

If anyone has any suggestions, I would love to hear them, especially for how to add a second tier to the mass to allow for more heat absorption area and mass heat storage. Should I make a second half barrel bench on top of the first one, or should I make taller bells, maybe bricking in some barrels which stand on top of the existing mass? I would really like to hear some suggestions.

Luke Perkins wrote:Do you know what your monthly winter gas bill/usage used to be?

I don't know if it's quite a cord per month. Hard to tell. Maybe.

When we moved in, the basement was unheated and we had a gas water heater. It used about $200 in gas per month. Replaced with a heat pump water heater so now we pay a couple bucks a month for hot water, and the stove provides functionally all our heat, heating both floors. So payback period will probably be a winter or so, since I spent so much on the ceramic fiber board.

UPDATE, January 2022

We cut off our gas service upon finishing the stove last spring, and we have been heating with the stove all winter, thus far. I am very happy with it, though I would really like to convert it into a batch box at some point in the near future, for all the reasons, number one is needing to split the wood less, then also, seeing the fire and stuff like that.

Luke Perkins wrote:What gauge steel is the feed tube?

The feed tube sits on top of the fire bricks which line the front end of the fiber board core. It is made of simple scrap 1/8" steel plate. There are also some pieces of angle welded to the bottom so it sits on the bricks nicely. The plate actually sleeves (sits inside) the top 1" of the brick. It extends up such that the total feed tube is about 18" when there is no ash.

Luke Perkins wrote:Did you weld it up or did you purchase it as is? Seems like a great solution.

I cut and welded it myself. After the first iteration seemed a bit throttled, I extended it by 1" so that it is now an inch longer than wide. The van den Berg air slot is about 1/4". I was told it would warp, and it did.

Luke Perkins wrote:You mentioned to me that you cut the feed tube to keep it from bowing. Which direction did it bow? How many slots did you cut into it?

The back, and sides warped inward. The slot warped very slightly in the direction of the slot, so that wasn't a concern. What I've done is used an angle grinder with a cutoff wheel to cut one thin slot in each of those three sides and bend it mostly back into place. So it's not perfect, but it works just fine. And this prevents issues many have with feed tube bricks cracking. I only have fire bricks in the bottom of the feed tube, extending to three brick widths into the burn tunnel. If were doing it again (or if/when I do an overhaul), I would line the walls of the burn tunnel further back, and the complete floor because it is slowly being eaten away by cleaning ash out and wood pieces getting shoved back there. Cooked fiber board has no durability when it comes to friction.

Luke Perkins wrote:How much wood do you typically burn each day/how long/how many times do you have to feed it?

One load of wood lasts 30-45 minutes, and we burn it 3-4 hours in the morning and 1-3 hours in the evening, depending on weather, or what temperature we want in the house. I built a wood rack that is exactly 4'/4' so about 1/3 of a cord. And that lasts 6-10 days depending on weather.

We bought a Harbor Freight electric wood splitter which is really nice for further processing wood that is too big. It's nice to have a wood splitter inside the house to make wood to order to fit in the feed tube.

As I have discussed somewhere, the core is of my own design, a scaled up version of Matt's 6" so it doesn't follow many of the golden rules. It is taller in the burn tunnel than is normal, which allows for quite a large amount of ash to build up before needing to be cleaned. 2-3 gallons of ash after it has been vacuumed out. It is also longer than typical, so that helps with ash also. And it uses ceramic fiber risers, for a total of nearly 5 feet of heat riser by the typical measurement. It never has draft issues. I have even started fires by lighting the top of the wood in the feed tube. Not advised, because it smokes, but it can do it.

Performance:
I have a high temp thermocouple in the base of the heat riser for monitoring and it is extremely useful, you should get one, full stop. It will keep you from overheating or running your system cold.

We try to keep the stove above 900 degrees. With the right fuel, something that is dense with a lot of surface area, like oak barrel staves, it can overheat. The CFB is only rated for 2300, so I try to keep it under 2200. If it does get that hot, I mist the wood with water to control it until it stops. Moral of the story, don't burn a whole batch of barrel staves at once, and you'll probably be fine. With normal wood, which for me is a mix of pine, fir, oak, locust, black walnut (don't @ me, it's rotten), madrone, spruce, cedar, and lumber scraps, I can typically get it to run in the 1200-1600F range, hot enough that the ash at the bottom of the feed tube will begin to form clinker.

The mass is too small, doesn't store up as much heat as I would like, and doesn't extract as much heat as I would like. Needs more surface area, perhaps a second bell. But there are limited options because it has to fit where it is. I did put a 55 gallon steel drum of water next to the barrel for added thermal mass, and it gets well over 100 degrees. It does sit somewhat directly on an uninsulated concrete floor, which acts as a large mass, though it loses plenty of heat out the bottom I expect. The floor next to the mass will often measure more than 95F. The normal floor temp averages in the low 70s.

We have a 44 year old house, 2x4 construction, sections of the bottom floor uninsulated, total of 3700 square feet, only the upper floor finished, and we are able to keep the upstairs at 68-72 during the daytime, though it does drop at night, which we like anyway. For a little extra instantaneous output, we sometimes use a fan blowing on the barrels, and a box fan feeds the under-mass air channels, and then we use some duct blowers sometimes to pull hot air upstairs in the morning. One day the house will have an HVAC system and be properly fully insulated, but not presently (I want to install an air to water heat pump with distributed air handlers, and an extra 4" of foam board to the outside). The bathroom floor directly above the stove stays toasty warm. The house was previously served by a 60k BTU natural gas furnace with forced air.

Another fun thing I've done is we have a heat pump water heater and I have ducted its intake to pull air from the bathrooms. One of them pulls air down the cavity that has the chimney in it. So that collects a little more waste heat, and since most of the heat comes from the wood stove (a little solar gain from windows) our hot water is practically free. Also helping with that is a waste water heat reclaimer that you can see through the wall in the above pictures. I've been meaning to post about "the case against wood water heating" for a while, I just never have. But here it is, heat pump water heaters are a game changer. If you have a natural source of heat (sun, wood, etc.) they are cheap and easy (compared to solar or other options) and they have the added benefit of free air conditioning in the summer, as well as free dehumidification. Further efficiency gains can be had by ducting the intake air from somewhere warm and moist (bathroom, next to the stove, attached greenhouse, whatever) and ducting the cool dry exhaust air somewhere either useful or where it can be diffused without creating discomfort.

The perfect fuel for this stove is 2x6s. It holds 4 almost perfectly, and they can be pretty long so it will feed for a couple hours, if you have that sort of thing around. When we moved into this house, I replaced a bunch of pieces on the back deck so we had a lot of that leftover.

If there are any other questions, I'm happy to answer them. I don't want to be one of those people who builds a stove and then is never heard from again.