The yurt manufacturer offers instructions, including this diagram:
As with all building plans, the drawing hides much complexity. For example, look at the height of that post. From the chimney tee to the wall band is about 7'. My tee is about 8' above the ground. That's 15' of post above ground. How deep should it be in the ground? They don't say. A common rule for posts is 1/3rd in the ground. That'd be 22' - a huge post! How would you haul one of those home? And a 7' deep post hole is a tough proposition! You're talking heavy equipment, but a hole that is only 15" away from the wall of the yurt - not much room to get in there.
The instructions have the posts 8" apart. It's just about impossible to dig holes for 4"x4" posts 8" apart and keep the holes separate. The barrier between the would be very thin. You could dig one bigger hole for both posts, and use a lot more concrete. However, 8" spacing is troublesome: the Chimney Wall Support Kit has its screw holes 11" apart O.C., and the Wall Band, way up at the top of the posts, has holes 16" O.C. Hmmm.
Ideally you want the horizontal part of the chimney to sit along a radius of the round yurt, a radius that hits an intersection of the lattice (you remove an X of lattice for the chimney). The posts must be equidistant from this radius. You only get about an inch of play here, to keep the wall bracket screws in the posts. Digging accurate holes is really hard, so you probably have to over-size them a bit, place the posts, and then fill in with concrete. The bigger the hole, the more concrete you have to mix and pour.
I thought I would rent a 6" gas-powered auger, dig 2 holes as deep as I could, and take advantage of the close walls of undisturbed dirt to hold the posts well. I now think this was a bad plan, since digging accurate holes is so hard. As it was, the rental place accidentally gave us an 8" auger bit, so our holes gave a bit more room to work with, and we took full advantage of that to get the posts placed well. Even so, they were off a bit, and we had to work to get the chimney aligned well.
We got 20'-long posts. These each weigh about 100 lbs. You have to stand them up on end in the hole, plumb, 15" from the yurt, and at the appropriate distance from the radius (within an inch). You can only measure their position correctly when they're plumb, and they're unwieldy, so you have to brace them long enough to take measurements, and then unbrace and move again. My positioning was not very good, and I had to compensate later by bending the wall support kit a little.
I thought about assembling the chimney on to the posts before erecting them, but then we're talking around 300 lbs for the whole assembly, and getting the tee at the exact right height is critical, so you have to wait until the posts are up.
I placed one post, braced it, and poured the concrete. After that set, I used it to brace the 2nd post, and pour that concrete. My calculations said I'd need 4 sacks of concrete mix, so I bought 5 and used it all.
This was my first concrete pour.
After giving it time to cure, we set about attaching the chimney. First comes the the wall bracket. This must be at just the right height, within 1/8" or so, so the horizontal section of chimney goes right through the flashing on the side of the yurt, and stays horizontal. (Some say to make it lower outside, so rain drips away; others say to make it lower inside, so creosote drips back to the fire.) To get this right, we clamped the bracket in place, put the tee on it, and attached the horizontal chimney piece to it. This is tricky because the assembly weighs around 60 lbs, and it's 8' up in the air. Once it's in place, you screw everything down and it gets stable.
The wall band at the top is wider than the posts by 7". I wanted to attach a short 2x4 up there as a cleat, and attach the wall band to it. The 2x4 has to go on first, as the wall band would cover where I want to drive the screws in to the posts.
To do it, I'd need the drill, a level, clamps, and the cleat. A rope to a bucket made it easy to pass stuff up.
All of this is 15' up in the air. Not only that, I have to be on the wrong side of the posts, as there's not enough room between the posts and the yurt to set a ladder. So it was a little awkward. For safety, I tied the top of the ladder to the posts, and made a loop of rope to put around my torso in case I fell.
On top of the tee goes 3 lengths of insulated chimney. These are heavy! We used a rope to pull them up, and my arms are still sore. Once their in place, you have to screw them together, and then secure the joints with a locking band. One of the joints didn't want to go together because it wasn't aligned right. I had to go down and remove the flashing so the tee could adjust to align the verticals.
This is a good point to talk about the flashing, in case you are thinking about following these footsteps. First, they screw directly in to the yurt lattice. The lattice is quite thin, and will split easily. Be sure to pre-drill the lattice. Second, finding the exact right spot for the screws is hard on the outside, since you can't see the lattice. I used self-drilling sheet metal screws, but I think long machine screws through both flashings might be good.
Once they were aligned, we wrestled them together, and attached the locking band. Then it was back up to the top to tighten the wall band, which was very difficult to reach from the ladder and impossible to see from my perch.
Once the chimney was up, it was time to work on the inside.
There is a piece of cement board propped up against the wall of the yurt. There's supposed to be a 1" gap; since the wall is somewhat uneven, my gap is somewhat larger. I used 3"-long machine screws, each with 3 nuts to hold the board in position.
The floor also needs protection. The easiest way is probably a sheet of steel. We went with another sheet of cement board, which is harder because it's brittle. Julie did her first tile work ever on this cement board, and it looks quite nice. Once that cured, we hefted the woodstove in to place. The clearances are tight, as the woodstove is 2' wide and requires 6" of floor protection on each side, and the cement board is 3' wide. If you get it there and decide to shift things over an inch, you have to remove the stove (it weighs hundreds of pounds!), shift the cement board, and move the stove back it to place (it still weighs hundreds of pounds!). Instead, we used some adjustable elbows on the smoke pipe to get everything to come together. It looks a little sloppy, but I'm still happy with it:
The vertical smoke pipe goes in to a flue collar on the stove:
The pipe is not perfectly round, so there's a gap at the seam. I wasn't sure how to seal it up. Also, if the smoke pipe was just left resting loosely in the flue collar, it seemed like there was a risk of it getting knocked out, or at least breaking the seal. I asked DIY Stack Exchange, but got no answers. I asked at the hardware store, andn they had a bunch of ideas, but nothing that really came together. Then I noticed 2 small holes on the side of the flue collar for screws. I slathered the crimped end of smoke pipe with fire cement, attached it with screws, and then caulked the seam with more fire cement, same as caulking a bathtub.
After a couple days of curing time, we were ready for our first fire. I collected some scraps and downed branches. I don't have full-size dry logs, so I also bought a 6-pack of pressed sawdust logs. We had friends come over and we enjoyed the fire together.
The yurt is all one room, with a high ceiling, so it takes a while to warm it up. But sitting around the fire is nice right away. And that's where I'm sitting to write this now.
