using metal in the burn tunnel and heat riser

I have a cast refractory J-tube core and perlite/clay slip riser which is quite insulative, and coals burn to ash every time. I also have a positive natural draft, so if I don't cover the feed after burning I will get constant cooling airflow. I think you may be getting too strong airflow during coaling which is stealing the heat. Wood that is not dry enough could also be an issue, though if you have the same wood you used to that becomes less likely.

Glenn Herbert wrote:I have a cast refractory J-tube core and perlite/clay slip riser which is quite insulative, and coals burn to ash every time. I also have a positive natural draft, so if I don't cover the feed after burning I will get constant cooling airflow. I think you may be getting too strong airflow during coaling which is stealing the heat. Wood that is not dry enough could also be an issue, though if you have the same wood you used to that becomes less likely.

Right. When I had the more massive perlite clay slip riser, the coals burned to ash every time, and yes, I also had to put my feed tube lid on over night to damp. I've reached the opposite conclusion now, though, on the airflow. Now the air flow seems to stop on it's own, as the riser cools so quickly after a burn. Sure the mass bench is warm, but not enough to create a draw it seems. And my water kettle cools after a few hours, too. Result of such a light weight core.  I have a small barrel on my feed tube, and I use the lid to slow air flow and usually close it off almost tight at night.
I tried an extra long, hot burn  yesterday, and also forgot to lid the feed. I had much better results. Some ash formed and it insulated the still glowing embers all night. Kettle was even slightly warm.
So my conclusion is that the 5 minute riser lets me cook more quickly, and therefore I've been able to have shorter fires and still have a hot meal and warm house. But the riser is so much less massive that in order to store enough heat to complete a fuel burn, I should keep her full throttle for at least an hour.  

Satamax Antone wrote:Laura, you might be missing some mass behind, and your draft is too strong. Maybe. Your firebox and burn tunnel still are made of bricks?

There is another thing which can do that, wet wood.

Ooo, damp fuel is a harsh teacher for sure. I have cooked and heated exclusively with wood for over 7 years now, and I'm still in love with fire. If there is one thing which I've learned:  use well-seasoned wood.  
As I write in my reply to Glenn, it appears lack of draw from too small of a burn may be my issue. Yes, the firebox and burn tunnel are brick, inside cob. Tons of mass in the bench around the exhaust. Old riser was especially massive, though, so it appears I'm just learning how to handle this lighter, more responsive one.