Chris Burge

Bruce, I'm trying to understand what it is that you are trying to accomplish.

Do you intend to insulate the J-tube? If this design gets up to temp, that metal is going to spall like crazy. However, I wonder how it will draft-- the riser looks terribly short for such a long burn tunnel. Will it vent through a mass? Do you have a sketch of the final intended layout?

Hey Kevin,

Give these two threads a read:

experimentation

implementation

This system:

-I built into an existing fireplace
-has a 4.5in CSA
-has a cast riser with an iron liner
-burns wood, pellets, or both
-was temporary...I used clay slip...the fireplace has been restored to a Rumford configuration

I wouldn't say that this design is a viable solution for your particular situation, but it might give you a few more ideas.

Jacob,

Thanks.

The feeder is just a couple of pieces of 3in exhaust pipe-- an 18in straight piece and a bent slant tip. I made a couple of cuts on the end of the tip and bent the center piece into a crude peg shape.

The bottom of the pellet feeder is an iron trivet with three 1in bolts as legs.

The peg rests in one of the holes in the trivet. The edge of the feed tube helps control the flow of pellets.
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The stove's outstanding draw prevents the feeder from backdrafting.

The barrel is a 7 gallon steel heavy gauge with a ring clamp lid. I picked it up at a local salvage yard.

I'm about to experiment with insulating the feed tube on this one-- I've got some ceramic wool and S/S band clamps that should do the trick. With the pellet feeder, it's not an issue, but when I burn it with just wood, the tremendous heat ignites all of the fuel in the feed tube all at once and causes the system choke itself down with embers.

I haven't used a stove like this for an extended period of time, and this one is only a couple of months old, but I know that the stovepipe doesn't hold up very well at the bottom edge of the feed tube where temps are highest. The barrel, however, is far more durable. Using the pellet feeder exclusively would make a system such as this last much longer-- the feeder setup keeps the fire in the center of the barrel and maintains a consistent burn rate. Although it remains to be seen, I suspect that the feed tube will hold up a bit longer when insulated.

This little stove just has a chimney, not a heat riser, and insulating it would defeat the purpose since a lot of radiant heat is emitted from the chimney itself.

I would not consider ones of these stoves to be as efficient or hold more wood than a "conventional" RMH, but they do produce high enough temps to result in a very clean burn.


Check out this thread to see the small format RMH I built that includes a pellet feeder.

https://permies.com/t/22486/rocket-stoves/mini-rocket-mass-heater

Just made a pellet feeder for the pocket rocket!

Al,

The evidence is clear, look at the chart, insulating bricks insulate. Their rate of thermal conductivity is determined by their composition, not their mass.

You're creating an issue where there is none and hence, creating confusion.

Fire brick, wood stove splits, smelter brick, kiln liner, foundry brick, all have very similar composition... So similar, in fact, that they have been given one category and have been assigned one value on the chart.

You're splitting hairs on a bald head... A red herring... There is no cheese down this tunnel.

Al, it seems to me that you may be misinterpreting the data...

The chart to which you are referring reads as follows:

Brick dense 1.31
Brick, insulating 0.15
Brickwork, common 0.6 -1.0
Brickwork, dense 1.6

The only differentiation between types of brick are "dense" and "insulating". These are obviously two highly generalized categories, but it's safe to assume that all types of fire/kiln/smelter/foundry brick have been lumped into the "insulating" category, regardless of of size, density or application. Therefore, all other types of non-insulating bricks have been categorized as "dense". The values for each are what we would expect-- bricks that are intended to insulate do so, and all the rest do not-- or at least, not as well. These two values also coincide with my qualitative analysis.

The next two lines in the chart are referring to "brickwork", which we can only assume to mean some form of brick and mortar construction, be it a wall, column, etc. The differentiation of these two categories, "common" and "dense", is between the types of work, not the types of brick.

On this point, Al, I beg to differ.

Red brick, old or new, is full of iron oxide and will conduct heat faster than any fire brick. In all of my experimentation with building and burning cores, I found that red brick, no matter what variety, did not preform as well as fire brick. Out was hard to achieve high temps and I had several bricks fracture from the heat stress.

The fact of the matter is that all fire brick is mainly composed of paloma grit which is mostly alumina and silicon dioxide. It's this specific composition that gives fire brick its ability to withstand higher temperatures and conduct heat at a slower rate. The slow transfer rate is essential within an RMH core where higher temperatures are desired. I built two cores using foundry bricks (the "heavy" kind) and not only did they perform beautifully, the bricks showed no sign of fracturing or surface breakdown.

Tom: The gap at the bottom of the feed tube is 2" and, yes, the wood rests directly on the bottom.

Al: I've found it's best to put these on top of three fire bricks to help prevent asphalt combustion