Permsteading.com

I used 3/8" particle board for the inside form of my core. Now I'm working on the heat riser. I formed a cylinder 31" high with a diameter of 19" out of sheet metal to give the supposedly ideal 1.5" clearance around the sides of a barrel with 22" ID (due to lack of appropriately sized barrel hanging around here). Then I went to get a smaller piece of sheet metal to form the 8 inch inside pipe, and I realized that the rest of my metal is rolled up in a fairly big roll left over from doing my standing seam roof. Being lazy to unroll and cut, I got to thinking:
What's wrong with a making a 7.25" square inside heat riser form from particle board?

It isn't a hypothetical question-- I made it, but then my wife needed help with the kids and now its late, so I'll see tomorrow when I make the heat riser...

Nothing wrong with it at all. In fact, that's what I do. I find that it's easier to repair a square riser than a round one.

So far so good. Now I've got a barrel inverted over the whole heat riser (outside) to help speed up the drying out. At first, before I put the barrel, I was standing around kind of bored tending to the fire. I had noticed that dropping paper down the heat riser gives nice bursts of flame, so being a pyro I did that. Apparently, the heat had been pyrolysing the MDF form but not igniting it, because immediately I got not a small flame out, but a five foot high flame shooting out as the MDF burned while at the same time drying further into the MDF and releasing more gases-- 3 whole minutes. It was awesome. I need to make some more heat risers so I can enjoy that effect more.