Hi Erica,
Thanks for your replies. I watched a lot of your videos when I build it and they helped me a lot! I think you're right about the space. It's very large and opens from the first floor, where I build it, right up to the second floor.
I get the smoke back only in the beginning nowadays and when I light it up and open the door to outside it keeps burning fine but if I close it it dies and I get smoke back. Rainy weather seems to make it worse. Once it's burning which takes about 30 minutes it keeps going the whole day and night without problems. If I start it up the next morning when it's still warm it will just fire straight into rocket position and burn fine but if I let it cool down it takes more attention.
The first one I build (which was the start of this thread) would start to cause problems once there was some coal building up in the burn chamber, the new one actually works better when there's some coal build up.
I filled my riser with clay and sand (no perlite) and it's much larger (thicker) than most I've seen as a compensation to my larger drum. This takes a while to heat up but gets very hot and after an hour of 2 burning can cook a complete meal (even brown rice and lentil) in about 1 and half hours or pizza in about 10 minutes. However the horizontal (not vertical!) exhaust never gets hot enough to warm a bench and the clay I put around it is not even completely dry after one month of burning!
So I have a very hot drum, that can actually cause burns when you accidentally touch it but the air is already very much cooled down when it get to the exhaust.
I like the fact that I can cook meals on it and it heats our house enough (living in Portugal, where winters are cold but nothing compared to Canada!) I'm still kind of jealous of the butt warming bench
so I'll probably build a second one with a bit more knowledge and hopefully a fully functioning bench, but I may keep this one for cooking and heat in my kitchen