To those of you who feel I've bastardized perfectly good stoves, I'm sorry I just can't help myself.
But, I've just finished my latest and hopefully last (for this season anyway) modification to my Chubby Stove.
My master plan for burning this season is to burn wood on the fringe months when it's warm during the day, but cold at night. And, to start burning coal later in the season when that day time temps average 45 and below. It's nice to have the option of letting the fire go out during the day, which isn't much of an option with Anthracite. To accomplish this I have to have good wood burning capabilities and the chubby isn't well designed for wood, IMO.
So rather than have two stoves on the hearth, I added an upper chamber to my Chubby and some secondary air piping. The chamber serves two purposes. First, it provides added surface area and baffling to act as a heat exchanger for the hot wood flue gases. Second, it houses a SteelCat catalytic combustor to achieve near complete combustion of materials and make full use of the wood burned. There's also a little black pipe running from one of the secondary air holes up to just underneath the combustor. A catalytic thermometer is mounted on the right, just above the combustor level. The outter wall is 1/8" mild steel (thicker than the steel on the Chubby), and the baffle and shelf the combustor is on is made of 3/16" steel to take the heat (probably overkill). A steel flat rolled into a ring (just like the one in the middle covering up the upper/lower divide) is welded to the inside of the catalytic chamber wall and allows the chamber to sit down inside the chubby, while the chamber wall is exactly the width of the chubby and sits on top of it.
I didn't have to weld anything to the Chubby stove. I did have to widen the secondary air hole by 1/16" with a step bit to accomodate the black pipe, but will still function normally if I remove the pipe. Since the upper chamber is the same dimensions as the Chubby body, the top casting just sits like it normally would on top. I added tabs like the Chubby has to bolt the casting to. This was a rear venting chubby, but I covered the rear vent with a 6" stove pipe cap and put bolts in the damper holes after removing the damper. The hole in the top casting now serves as the flue vent and a piece of 6" stove pipe fits snuggly through the hole down a couple inches into the stove. A steel ring (not yet painted) sits around the stove pipe in that little lip in teh casting and pinches some 3/8" gasket to the stove pipe. It's not really needed, but I 'm paranoid about air tightness.
The couple test burns I've had so far have been successul, achieving 1000 degree output on the catalyst and no smoke from my chimney.
Now for the controversial part: Bio Bricks are the perfect wood fuel for the Chubby Stove.
I'm talking about the small ones, Bio Bricks, Hot Bricks, etc. The other compressed fuels like Envilogs and Eco Logs, etc are too big for the firepot. But the small bricks pack/stack in the firepot nicely, are so so dense that they burn for hours, and have almost no creosote. From a cost perspective, $259 for a pallet of bio bricks is equivilent to 1 cord of wood (though I think it's actually more than a cord in BTU and efficiency). Seasoned cordwood in my area is $200/cord give or take. Sometimes you find cheaper, but it's usually pretty green when you see it in person. So while it's more expensive than cordwood, for me, it beats splitting and stacking and of course chopping down to fit the Chubby's small firebox.
Love'em or hate'em, brio bricks kick butt in a Chubby Stove. And, with the SteelCat installed, I can turn the stove down low and get overnight burn times with the cat cranking out 1000 degrees temps. The automatic draft damper I installed helps a lot with that, though with wood I've had to cover up half the opening inside the draft box with a steel plate to get the wood fire down to a low/slow burn. I don't need much intake with wood compared to coal it seems.
Here are the outter pics. I will take some pictures of the inside tonight.