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Post by peterberg on Jun 26, 2014 10:55:32 GMT -8
Batch box door on the right, and a cleanout door for the riser just to it's left. Skip the cleanout door for the riser, in a well-built stove there won't be any ash at the riser floor. Besides that, it's dead easy to reach the riser by hand or with a small brush. On the other hand, a clean-out door for the bell floor would be handy. Fly ash will be accumulating there so probably cleaning once in one or two years would be adequate. On the topic of insulation: It's much better not to fill the entire space around the firebox but make a steel sheet around it and fill that with insulation material. As an alternative: only insulate the riser that would work nearly as well. Any heat coming through the firebox walls will end up in the bell so is not lost.
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Post by peterberg on Jun 26, 2014 11:01:20 GMT -8
@jlr, Looking at your drawing, there are two pipes from the floor of the fireplace up to the throat of the former hearth.
Better to use just one, gives less friction than two of the same accumulated CSA. And insulate that duct, otherwise the pipe itself will loose heat by conduction through the metal and heat up the exhaust gases again.
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Post by satamax on Jun 26, 2014 13:25:11 GMT -8
As i've said many times, retrofiting a fireplace and chimney, with a rocket is doable, using the chimney as a bell, with a plunger tube, and blocking the chimney at a proper height to accomodate for a 6m² isa. See my sketchup drawings.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jun 26, 2014 18:32:02 GMT -8
As i've said many times, retrofiting a fireplace and chimney, with a rocket is doable, using the chimney as a bell, with a plunger tube, and blocking the chimney at a proper height to accomodate for a 6m² isa. See my sketchup drawings. Sorry Satamax, just working out the details and trying to innovate a little around my constraints. The second plunger tube is assuming I can't fit a 7" stove pipe in the space provided, or through the damper plate. Despite others telling me it will work, it is still a financially risky endeavor, compared to simply buying a fireplace insert. I need to validate various aspects of the system with all you experts before I take the plunge, pun intended.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jun 27, 2014 11:01:28 GMT -8
Batch box door on the right, and a cleanout door for the riser just to it's left. Skip the cleanout door for the riser, in a well-built stove there won't be any ash at the riser floor. Besides that, it's dead easy to reach the riser by hand or with a small brush. On the other hand, a clean-out door for the bell floor would be handy. Fly ash will be accumulating there so probably cleaning once in one or two years would be adequate. On the topic of insulation: It's much better not to fill the entire space around the firebox but make a steel sheet around it and fill that with insulation material. As an alternative: only insulate the riser that would work nearly as well. Any heat coming through the firebox walls will end up in the bell so is not lost. What about an ash cleanout door below the door to the burn tunnel? Isn't ash a perpetual issue in the burn tunnel? If the center (between the two 45 degree walls) of the burn tunnel was a cast iron grate with some void space below it, you could do something like this with a cleanout drawer.
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Post by satamax on Jun 27, 2014 12:36:21 GMT -8
Don't bother. IIRC, it proved to be bad for the burn. Plus, if your firebox is well insulated, it won't be that much of a problem. Cleaning may be once a week. just raking the ashes into a bucket or tray under the firebox end.
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Post by DCish on Jun 27, 2014 12:59:29 GMT -8
jrl, regarding the 7" "plunger" flue, many threads have referenced using a slightly smaller flue than is used as the system size in the core. This is because of the loss of volume as the combustion gasses cool. So if you are going for a 7" core you could be able to get away with a 6" flue. If your core is 6" you would be certainly be able to stay with a 6" flue -- others may be able to comment if 5" would be sufficient.
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Post by satamax on Jun 27, 2014 13:58:02 GMT -8
I'm using 6 into 4 ish 111mm
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jrl
Junior Member
Posts: 101
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Post by jrl on Jun 27, 2014 17:09:12 GMT -8
jrl, regarding the 7" "plunger flue, many threads have referenced using a slightly smaller flue than is used as the system size in the core. This is because of the loss of volume as the combustion gasses cool. So if you are going for a 7" core you could be able to get away with a 6" flue. If your core is 6" you would be certainly be able to stay with a 6" flue -- others may be able to comment if 5" would be sufficient. I would have thought the plunger should be >= the csa of the riser. You're saying it should be smaller than the system size?
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Post by DCish on Jun 27, 2014 20:19:50 GMT -8
Chimney performance is related to height, temperature differential, and resistance. Gasses shrink as they cool, so a smaller flue can carry the gasses at the same speed without added resistance. A taller chimney will give you more draft ("pressure"), a larger diameter chimney will not. Indeed, increasing the diameter of the chimney beyond what is needed to ensure minimal resistance (system size or slightly smaller) could make it perform more poorly as the slower-moving gasses have more time to cool before exiting at the top. Thus you would need to expend more heat to drive a larger than necessary chimney to compensate for the heat loss and attain the same amount of draft as a properly sized chimney.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jun 29, 2014 19:11:38 GMT -8
Further inspection and measurement of my chimney reveals a large, cast iron, angled bulkhead/frame and a cast iron damper plate. Positioning of the riser would leave the super heated exhaust beating on the frame and damper. Also the brick up there is not firebrick and refractory in the last 12 inches before the damper. I'm concerned about long term damage to the cast iron and mortar up there.
Couple questions:
Should I place a sacrificial steel plate (got 3/16" laying around) some inches just above the riser? Will this interfere w/the rocketiness of the system? It would be like putting a chimney cap on the riser.
As was suggested, I plan to insulate the backer plate that will replace the damper, and the plunger tube, and the riser & firebox. I've ordered a roll of ceramic fiber blanket (I have a respirator) rated to 2300 degrees. Can that material alone take the beating of the immediate exhaust?
Regarding wrapping the riser in that stuff, is there a need to have an outer shell, or can that material be tied with wire or mesh to the riser and left exposed? Aside from getting dirty, is there any risk of degradation in its insulating properties?
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Post by satamax on Jun 29, 2014 20:42:14 GMT -8
I wouldn't use a steel plate to protect the top myself, mind you, it could reduce the violent movement of gases and help stratify.
With the damper plate open, you have enough space to fit the plunger tube? What is your planned ISA? Remember, around the plunger tube, use insulation to block the chimney off, at the right height for the required isa. May be use a steel plate or something to hold the insulation. It all depends on what you use.
The usual way to hold cerablanket around a riser, is chicken wire. You can use thin sheet metal also. It shouldn't degrade, it's ceramic, nor it's insulation properties.
IIRC, i've read few here and elsewhere who stated that inside the bell the temps were in the range of 400C° to 600C°, not realy refractory land. May be the mortar will need replacing in ten years, on the outer surface, but i doubt heat damage will go far in between firebricks.
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Post by DCish on Jun 30, 2014 2:51:27 GMT -8
Regarding the "sacrificial" nature of the steel plate: in by-the-book construction there is a steel barrel directly atop the riser, and it lives a long and healthy life. The reason given for this, I think in Ianto's book, is that by the time the gasses exit the riser the oxygen has largely been consumed, leaving little remaining to carry out oxidation.
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jrl
Junior Member
Posts: 101
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Post by jrl on Jun 30, 2014 6:20:57 GMT -8
I wouldn't use a steel plate to protect the top myself, mind you, it could reduce the violent movement of gases and help stratify. With the damper plate open, you have enough space to fit the plunger tube? What is your planned ISA? Remember, around the plunger tube, use insulation to block the chimney off, at the right height for the required isa. May be use a steel plate or something to hold the insulation. It all depends on what you use. The usual way to hold cerablanket around a riser, is chicken wire. You can use thin sheet metal also. It shouldn't degrade, it's ceramic, nor it's insulation properties. IIRC, i've read few here and elsewhere who stated that inside the bell the temps were in the range of 400C° to 600C°, not realy refractory land. May be the mortar will need replacing in ten years, on the outer surface, but i doubt heat damage will go far in between firebricks. Chicken wire, that's a good tip, thanks. I have a roll of heavy gauge chicken wire stuff laying around (it'll stop everything short of a bear from eating your chickens). I bet the thick wire mesh would work to jam insulation up in the cavity just before the damper frame/plate. That'd stop the cast iron and old masonry from taking the beating. Plus, if what DCish said hold, then oxidation isn't a real issue anyway. The ISA is something a little less than 3m^2. 75% of it is fire brick walls. 25% of it is the steel facing that will radiate to the living space. Everything surrounding the fireplace is old cape-cod looking red brick. It's just the size limitation of the fireplace that drives the small ISA. I've reduced the planned CSA of the system to 5" and batch box dimensions following Peterburg's formula. The firebox will extend out onto the hearth 2-3". The door to the firebox would be build with steel flats, probably 1/8" or 3/16", whatever I use for frame of the steel facing. I'm hoping to put some fireglass on the door as well. I imagine the door and facing is going to get really, really, hot because it's the only easy conduction of heat before exiting up the chimney. As for the plunger tube, my plan is to build a boot (like a duct boot) to fit 1/3 of where the damper is. Opening is maybe 5" x 24" (guessing, haven't measured the damper yet). The remainder of the opening would be plated off with steel. BTW, the chimney is a US standard masonry chimney, big 12" clay flue tiles mortared within an old red brick chimney, exiting a several feet above the highest point of the roof line. There's a stone slab cap on the chimney. The duct would transition to 5" round black stove pipe (5" round < 5" square csa). Is galvanized ok? It would be cheaper. I'll have a couple adjustable elbows in there to manuever around things down to 3" or so above the floor as you had suggested. If everything, including the plunger is wrapped in ceramic blanket and chicken wire, do you see any other glaring issues with this design? And, a picture is worth a thousand. Here is a rough mockup setting in the fireplace: Keep in mind, this is not intended to be some super-efficient masonry or mass heater. There's no mud slopped cob bench or anything. My goal is provide space heating in my living room by burning wood in a more efficient and less smokey manner than simplying lighting up logs in the fireplace. I want to burn scrap and tree branches and thinly split firewood. And, only in the spring and fall on cool nights. Get home, start it up, and let it run for bit. Then, I'm hoping the heat built up in the firebrick and hearth will radiate for a while until we go to bed. I burned 4800 LB of anthacite coal last winter in a freestanding stove that sits on a bigger hearth directly below this one, and there are floor vents that allow convection to the upstairs. Coal stoves are one of those things you fire up and run 24/7 for months on end. It's not easy to clean out and start up frequently. Thus, it's not very good in the fringe months when it's warm outside during the day, but cold at night. Now, when the day's high is 12F and -3F at night, my house is toasty warm with the coal stove. So just keep the purpose of this rocket in mind. It's intended to be glorified space heater for my living room. Duct boot example:
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Post by satamax on Jun 30, 2014 12:15:00 GMT -8
JRL, you say 12" tiles in the chimney? So is it 12x12? if yes, i would block the chimney further up, to increase the isa a bit. If you go 1m up in the chimney, you'd have gained 1.2m²Leave the damper plate fully open, or even, borrow a plasma cutter, and cut it off. Insulating the plunger is a good idea. Mind you, for this, rockwool is suficient, no need for fancy and expensive cerablanket. Instead of elbows and a boot, i would just slide a piece of cut tube either inside or outside, that you can bring up or down, and rivet in place when you've found the right spot.
If i was doing something like this for myself, i would push the heat riser all the way to the left, and make the batch box cental.
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