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I've been back through the photos again, man, this thing is going to be a great heater. At first glance I didn't follow the flue path properly, I like it! Those brick plates making the flue path, very cool man. One suggestion if it's not too late...Make that last chamber, the one that couples to the chimney, accessible. You will want to be able to clean that out easily, and inspect the chimney seasonally. These things can create a super light fly ash "web" structure that can eventually obstruct the flue runs, even way up there. Make sure you can get to it and clean it. Otherwise, man, I love this build. You are going to have a good time finishing it, and I'm sure it is going to be a warm winter in your house next year.

Its done!

Well, except that I forgot about the need to partially close the feed hole, so I need to make some sort of bracket/ledge to support whatever brick is used.

Right on Andrew! Man, it looks great, very nice work there. I love how traditional it looks. Have you run it enough to get a feel for how well it heats the other side of the connecting wall? Do I have that right? I seem to remember it was against a wall that connected to another room.

Wow! That's really cool! I can't wait to hear how it performs for you. I love that you have that oven built in. I hope it gets as hot as you hope. Thanks for sharing your progress. It's really awesome to see what you have done.

When I burned it in the spring for few days the wall started to feel warm on the other side of the barrel. It isn't really cold here yet, so two nights ago, when I took this video, it was 70°F outside. I was mainly checking for smoke-tightness. You can see that the wood floor ends about 18" around the feed tunnel. Earlier that day it was just bare gravel foundation, and a test burn then discovered that, evidentily, there is a crack inside the smoke tunnels to the foundation that lets the intitially cold smoke seep out a bit into the gravel, where it was coming up through this open area. Now that the somewhat experimental lime plaster floor is in that space, no smoke. Maybe the smoke going into the gravel will help to preserve the underside of the wood floor.

The oven-like area is not actually for baking, but for making yogurt or kombucha or rising dough for bread-- anything that needs to be around 100-110°F.

There's also a heat-exchanger buried in the bench (the bench wound up being a bit smaller than I had planned) that will connect to a water heater on the otherside of the wall where the new bathroom is going. It will be a dual source water heater that can also heat from electric. I will test first though how well the heat exchanger works by attaching a small radiator to it.

Thanks for the compliments!

oh, and with the plywood around the form. I removed, as suggested, what surrounded the form, but the bottom piece of plywood I wasn't able to remove. Last week as I was plastering around everything I noticed the edge of plywood sticking out from under the core was loose-- all of the plywood under the core had burned off except the very edge!

Yeah, they will burn the outer mold for sure. Now you have an air gap! The heavy cold smoke finding the cracks is normal on cold starts, but that will stop once the whole thing is warm for the winter. At that point it's always drawing in. It's a good idea to seal it up everywhere you can, but there's always little leaks somewhere in my experience.

I had a great conversation in DC with Austrian Kachelofen master Richard Jussel about this. He was expressing his amusement at some of the suggested testing methods of pressurizing masonry heaters to test for cracks. He was laughing saying they always will have cracks and gaps, and if they don't they will. We had a great bonding over this, since as you guys know I'm pretty fond of dismissing folks worrying about cracked cores and crappy seals in the mass and what not. It was great to get some reassurance from someone who is carrying generations of knowledge and experience that that is the way it is. So, nice work Andrew!

I know these Kachelofen-- the first time I came to Slovakia I stayed in an old house in Levoca with these funny, ceramic wood-burning stoves in the rooms that I didn't really burn long enough to heat up my bedroom enough for the heat to hold through the night because the firebox was teeny! But I could imagine how one might keep it burning enough during the day that it would stay warm all night long. These are still not totally uncommon here and my friend just had one build in his new house last year, though he also has a central heating system with radiators for most of the house.