JZ, Did you do this in Fort Collins? I have a stump I need to remove and this sounds like a good approach.
Nope. Colorado is not a 'right to burn' state.
Burning "Yard waste" which I interpret stumps to fall into, is prohibited by city/county/Poudre Fire codes. In fact all open burns are.
However, 'contained' recreational and cooking fires are acceptable. Perhaps, you could scrape around the stump to bare soil, put some rocks or blocks around the edges and set a metal BBQ screen on top of the stump.
:)
I would not recommend this approach however. I know others have done it, but roots (given their interface with the soil) have higher moisture content than dead and downed wood. That means, the stump could smolder for a long time and the coarse root channels as well. Believe me, I have mopped up stump holes in wildland fires. That involves digging a 10' wide pit, three' down and mixing mud to extinguish coarse rots.
Even if you wait until a day before the snow flies to light the stump, smoldering roots (and the surrounding soil) can hold heat through the winter.