Aslan Core Gets a Mass (Image Heavy)

The mass is complete. It wasn't dry in some of the pictures, which were taken a week ago, but it is pretty much dry now. This top picture was taken this morning.

Some cracking, but I'm going to finish it with tile or something, so it won't matter.





Another view, just so you can get a better idea of the layout.





I really enjoy the arch. I just used a leftover piece of barrel as a form.  This is a 10" cleanout and inspection port, the biggest I could fit in the end of a half barrel.





This is what it looks like inside the cleanout. The exhaust snakes back to the end of the bench to force gas flow all the way to the end.




This is a view of the wood feed. I enlarged it an extra inch during testing. Works really well now, is now capable of thermal runaway if you try hard enough. With normal firewood it is fine, but I am able to overload it using small dense wood well packed, like old barrel staves.
Dimensions are 6 1/2" by 7 5/8" including the P-channel.


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Operationally, it works extremely well from what I've read about other's experiences. I have never had to prime the chimney. Draw is exceptional at all times. Maybe even excessive, I don't know without exhaust testing. I feel like it may be running lean.

Starting is very easy, simply stack two handfuls of kindling against the burn tunnel side of the wood feed, propane torch for 30 seconds, then insert firewood. Takes about ten minutes for the chimney to be fully heated and water vapor to disappear. Never smokes back unless I'm goofing with it somehow. No smoke unless burning cold, for instance if the wood is jammed in the feed and hanging off the floor.

I have thermocouples built in, one in the heat riser, one in the bottom of the manifold, and there will be one in the chimney soon and one or more in the mass eventually. Presently, I measure chimney temps with an infrared thermometer. Normal operating temp is around 1000-1500F, but can range from 800-2400 (if overloaded). Final exhaust temperatures range from 130-230, usually 175 +/-.

We have had no problem at all heating our 3700 square foot 2-story house with 2x4 walls, though it's not deep winter. We have been having frost at night, so still somewhat representative. More often that not, my wife now complains of the house being too warm. I have been running one or two loads of wood in the morning, and one in the evening, mostly for fun to dry out the mass.

It's neat to walk in the room in the middle of the day and feel the radiant heat.

I would like, or would have liked to have had a larger bench, but this is the space that was available. This system could definitely handle it and it would make it more efficient. I have been thinking of ideas for a second bell or something connected with pipe vertically out of the bench to draw more heat, maybe like one of those radiant things in the ceilings of outdoor departments at big stores. I wonder how well that would work.

Solomon;    
That is a superb build!  
Looks great and sounds like its working great as well!
You did very well playing with bricks!  I like the arch as well!

What a great build Solomon! Very clean and pleasing to the eye. Thank you for sharing.

Nice brickwork!
That thing would eat half of my livingroom.

trevor tutt wrote:That thing would eat half of my livingroom.

Depends on your living room. It's three feet wide, four inches from the wall, around 17 feet total length but a lot of that is taken up by the corner, so it's not quite as big as that in terms of mass.
I had intended it to be big enough for a twin mattress, but I don't think that's happening. I need to get the top finished so we can sit on it.

Looking great Solomon.

Looking forward to seeing your stove in person soon! What gauge steel is the feed tube? Did you weld it up or did you purchase it as is? Seems like a great solution. 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?

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

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.

Thanks for the detailed follow up! Very helpful. Looking forward to seeing the stove in person!

So, sounds like 1/3 a cord every 6-10 days? So a cord+ per month. Definitely going through some wood, but it's a large house (three times as large as a 1200 sq ft' double wide). I'm actually impressed that the heater is able to heat such a large space. Do you know what your monthly winter gas bill/usage used to be?

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.

I love this you did a fantastic job, and the savings will be phenomenal for many years to come. i have been studying Russian masonry stoves for decades and bound and determined to have one someday or something similar to yours or the yew  eagle house I have studied as well. If buy another or build will be one first things I do. My issue with this home is huge FB, so wood insert, so where to locate wish I could incorporate it as your design would rock it out, but tile roof so not sure how could do pipe here with the tile... I have been awaiting at another place a stove  finally settled as mine, I hope still there an Irish wood stove so between all my house little smaller than  yours would do great in winter, and for cooking hot water etc. I waited and researched that stove decades, finally found, and bought but ex took so now I hope finally able to bring it home.