Interesting, flame bring pulled under grate

[wobbletop]

https://imgur.com/a/QtxQi4i

Just noticed this interesting thing happening under the grate in my barrel evaporator. I have air being fed at the bottom through a tube with holes from a bathroom fan. The holes are squished but making do.

If I turn down the air flow, the flames stop coming down through the grate.

Thoughts? I'm thinking to share turn down the air so this doesn't happen

[maple flats]

That's likely because the wood gas is starving for oxygen. Get a bigger fan, more CFM. Most bathroom fans will be between 50 and maybe 75 cfm, you likely need a 150 cfm blower.