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.