G. Karl Marcus

Danette,

Any relation to Wayne, from Camus Prairie?  Old friend from a previous life.

As I see the situation, you're planning to tunnel into alluvium.  Sounds like a mining venture.  You might want to consider how to stabilize the seven feet of overburden during construction.  As for protecting foundation walls from frost heave, the two side walls and rear wall should be sufficiently buried to prevent any disturbance from frost.  Only the base of the front wall, and perhaps a short return on the side walls will be close enough to the surface to be vulnerable.  If you go up Valley Creek a short ways and walk up the steep slope to the north, you'll find an old homestead.  Look for the lilacs.  Northwest of the house foundation you'll find a root cellar with a barrel-vault concrete roof.  It's pretty cool.  Are the rocks on your property predominately red?

I grew up in Arkport, N.Y., but currently live in southwestern Montana. You could try growing catnip, interplanted with borage and hollyhocks. The flowers will draw pollinators, and the catnip will seed everywhere. It'll drive the whackos bonkers.

I'm planning to pre-cast a heat riser using Mizzou and perlite mix. I want to use a six inch dia. sonotube inside a ten-inch dia. sonotube to form the riser. This will give me an insulated, hard-faced riser with a six inch interior dimension, a wall thickness of about 1 3/4 inches and an outside diameter of 10 3/8ths inches. I have a 16" diameter water tank to drop over the heat riser. My question is, if I cut the tank so that the riser is two inches shorter than the tank, how tall a riser is optimal? The tank is presently forty-six inches long. Sonotubes are 48 inches, so I have options. Just wondering if there are optimal dimesions and proportions, before I go to cutting things up. Also, heater will be used to heat a greenhouse space, if that makes a difference.

I'm using Mizzou and perlite because they're both white and my theory is that the color will help to keep temps a little higher. Also, has anybody played with injecting secondary air at the base of the heat riser, specifically at tangents to the riser diameter in order to spin the flame and create an elongated flame front? Any feed-back would be most appreciated.

-rockpicker

Ernie; The stove featured in the article found here: http://www.finehomebuilding.com/how-to-articles/kang-masonry-stove.aspx?ac=ts&ra=fp
was built by me in Missoula, Montana, in 1986. As you can see, the k'ang had a fairly large secondary burn chamber, about 40 feet of horizontal flue separated by firebrick walls and a cement block/clay liner, 8x12 chimney that stood in the corner of the room and was about 15 ft. in height. Flue runs were nine inches by approximately fifteen inches tall. Eventually, the firebox was fitted with an airtight steel door. As reported above, the stove burned vigorously, producing little smoke and no creosote. Primary and secondary pre-heated air was supplied through the door arrangement. Adding the door made the stove burn hotter and cleaner, as it offered control over excess air rushing through the system, and it allowed for some pre-heating of combustion air.

Cleanliness was never a problem, and it ate like a bird. One problem that did arise was perplexing. After a string of bad-air days, when the stove was cold, closing the door on a vigorously burning fire caused asphyxiation, and smoke problems. After repeated attempts, I finally reasoned that the bricks inside the stove, (probably 400 or so), were so cold they were absorbing all the heat from the flue gas before it got to the chimney. If the flue gas didn't rise up the chimney, fresh air would not be pulled in through the door frame. So, to solve the problem, I began burning the first fire after cold snaps with the door open. Problem solved.

Clean-out door at chimney-base offers a simple way to remedy any back-draft problems. If the stove is cold, a small wad of newspaper, or a weed burner, will easily and quickly reverse the flow. Typically what came up the chimney was clean, moist exhaust cool enough to put your face in, and a little fly ash.

The function of the steel drum and heat riser is purely for immediate heat, either as a space heater or for cooking. A good chimney placed at the end of masonry flue runs, with no heat riser post-firebox, will burn just fine. It won't boil a teapot, though, unless a special cook top is designed in. So, it's important to examine your needs. If you want the barrel for quick space heating and cooking, by all means, go for it. But if long term thermal storage, with slow release, is the goal, I would dispense with the heat riser and barrel. It's simply not necessary. Access to the chimney base will allow you to establish draft enough to light the main fire. Once it starts, you always have a positive draft. That was my experience.

I would love to see some follow-up on this. Specifically, how critical is the immediate heat element to overall design function? Does the barrel overheat the air space? Is there too little mass storage being effectively charged?

Years ago I built an under-floor heater in Missoula. An article about it appeared in Fine Homebuilding magazine in the 80's. If you go to the link below, you can see a photo and drawing which, together, give a good idea of the lay-out. The system had about 40 feet of horizontal flue in five runs with four 180 degree bends, (ie. significant drag,) yet it drew and burned well. The masonry chimney, which stood in the corner of the room, was, in essence, the stove's "heat riser." I always felt, had the floor been supported by columns, rather than flue tunnels, the decreased inherent drag would have allowed for increase in overall stove size with no loss of efficiency or function.

http://www.finehomebuilding.com/how-to-articles/kang-masonry-stove.aspx?ac=ts&ra=fp

Anybody here thought of making the heat riser throat a water jacket, instead of wrapping the outside of the barrel?

During initial start-up there will be a certain amount of unburned hydrocarbons, smoke, in the flue gas. As the fire progresses and firebox temperatures increase, the amount of unburned hydrocarbons will diminish to negligible. I believe there is always some CO present in the flue gas until the active burning phase is complete. Rule of thumb among the masonry stove builders has been to assume CO presence until the flame disappears and all you have left is glowing coals, at which point it is safe to close the damper at the stove/chimney juncture.

Oroborus; Did you get a chance to open the link to the Fine Homebuilding article? I built that stove under a greenhouse/atrium space attached to a residence in Missoula, Mont. in the 80's. It had approximately 40 ft. of horizontal flue run in five runs with four 180 -degree turns, and it drew like the space shuttle taking off. Draft in these devices is rarely a problem, and it is a problem easily alleviated. Notice the cast iron clean-out door at the chimney base, above the floor, in the left side illustration? That's critical for cold weather operation. If the stove is not kept warm and the inner bricks are allowed to 'get cold', the stove will draft backwards upon firing, with quite unpleasant results. The clean-out door at the chimney base allows you to establish a positive draft in the stove BEFORE lighting a fire in the firebox. Once draft is established in the right direction, the main fire can be lit and will draw properly until the fuel load is consumed.

Cobb is a cheap alternative to high-quality refractory materials. In the primary and secondary combustion zones, I would suggest spending the extra bucks for top notch high temp materials. Downstream, I would be more apt to switch to cheaper materials, as anticipated temperatures should not require expensive refractory to guarantee component longevity.

Secondary combustion air is certainly a design requirement, and has been handled by other designers in a variety of ways. Pre-heated, secondary air, applied strategically to the flue gas stream where it passes from the firebox proper into the secondary combustion chamber is the ideal location. This delivery system might be constructed of stainless pipe exposed to the fire and connected to and pulling its air through a hollow door frame.

One design element missing in most of the talk I've read about rocket stoves is the relationship of excess air control to maximizing combustion. What I found in operating the k'ang in Missoula was that, prior to having an air-tight door in place, the stove would roar away with itself, taking in all the air it wanted and sending a great yellow flame all the way down the first flue run, and presumably, beyond for who knows how far? Yet, there was always some smoke associated with this type burn.

When the door/ air control was installed, turbulence was minimized, the yellow 'thrusters' turned blue and shortened, with the result being much more heat was dumped into the floor over the expansion chamber/first flue run than had been the case previously. Essentially, their is an optimum balance to be achieved through carburetion and an air-tight door, with controls, allows one to experiment with settings until a satisfactory balance is attained.

Oroborus; Just a quick response. I haven't been around gassification much, so I don't know if this is practical, but what if one were to build a masonry firebox, such as is shown in this photo from Fine Homebuilding?

http://www.finehomebuilding.com/how-to-articles/kang-masonry-stove.aspx?ac=ts&ra=fp

Then, beyond the firebox, you lay out two walls of firebrick, or other suitable high-temp material, say 8-12 feet long, maybe 18 inches wide, or so. Lets say three bricks high, or 7 1/2" high. For the roof of this expansion chamber, instead of refractory slabs, you build a steel box the width of the two walls and, say 24 inches deep, with a hinged lid. This box, you fill with a mixture of dried animal manure and wood pulp. Then you plumb the box so that gasses driven off are returned to the firebox. All this is assumed to be outside the greenhouse, and heat derived from the process is vented through masonry channels or steel duct beneath the greenhouse floor, to the north wall, which might be baffled and masonry doing double duty as a chargeable trombe wall, atop which sits the chimney exit.

Any safety risks in any of this so far?