Should it Burn?

I've heard the story about the guy who went a whole winter by just burning junk mail in his RMH. I've heard that bark doesn't burn so hot, that it leaves too much ash so isn't a great thing to fuel an RMH. Besides regular seasoned cordwood, what are some pros and cons of burning other stuff?

In a recent podcast Paul recommended burning cardboard to aid in starting and accelerating a burn. When I learned recently about the PFAS content common in cardboard these days, I had shifted my own practice to taking cardboard to the dump for recycling.

A month ago I talked to the local DNR expert on water conatination, of which PFAS is being found to be an emergent problem, and he reassured me that PFAS molocules will break down into harmless sub-particles above 1200*F. This led me to believe that there was no problem burning cardboard in an RMH as they should be running around 1800*.

But now, watching my J-tube operate and thinking back to Uncle Mud's lectures on the process, it occurs to me that something like cardboard leaves behind visible ash in the feed tube. The real heat from the rocket engine comes as gasses mix after the bend at the base of the riser.

So I am doubting the base of the feed tube gets much hotter than a regular stove, which I think is around 900*? It seems possible that what is left in the feed tube from PFAS contaminated cardboard retains the PFAS, and any ashes pulled out of there after burning cardboard shouldn't be used as an amendment?

The good news I guess is that if any PFAS is coming out of the cardboard into the gasses during the burn, it will be destroyed in the riser and not persist anywhere downstream of that.

I can't help with your question as I know nothing of the operation (yet) of a RMH.  I will be watching for the answers from the folks that may know!

Peace

Cardboard by itself may not be able to make a hot enough fire in a J-tube, but mixed in with a larger amount of firewood, even the temperatures at the base of the feed tube should disintegrate it, if not immediately, over the course of a burning session or so. I would not make cardboard the last thing you put in.

I always run my J-tube at least 3/4 covered, and the blast of air and confinement gets the bottom of the feed tube bright yellow-hot in places (sometimes purple flames, which I see at the back of a kiln firebox pushing 2000 F). I push the coals into the burn tunnel when adding logs, and everything gets incinerated without exception.