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I have noticed that all of the double
and triple wall fireplace flue pipes that I have seen are stainless steel on the center piece of pipe. I know that stainless steel is a much harder and more durable material than regular flue
pipe, such as the piece that runs from the woodburner to the wall or cieling but I wonder why and if the inner piece
of the flue pipe has to be stainless steel?
And while I am wondering about fireplace and wood heating things, I am thinking about the feasibility of putting a woodburning stove in an attached outbuilding just large enough
to get setbacks for combustible surfaces and drawing cool air through
a return duct and forcing hot air from the woodburner into the crawl space for a radiant or warm floor system in my
93 year old victorian btu eating home.
Replies
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Brisketbean, I think you answered the first part of your question....Regular metal pipe just doesn't hold up. I have taken to scrounging 6" & 8" stainless chemical transport pipe out of paper mills or chemical plants. It makes a great pipe to go from your stove to the chimney. I think triple wall chimneys are borderline dangerous (as fire hazards).
*Mr. Bean, may I call you Brisket? - I'm not aware of a code requirement for stainless in the flue pipe - just the double wall as insulation from combustible materials in the walls/roof. But stainless is good because of the corrosive natural of flue gases. Not down near the stove where the flue gases are hot. Acidic vapors, surprisingly, are not that bad for metal. But when they condense - that's bad for mild steel. So if your flue gases cool to 212F and water vapor condenses, then you have liquid acid inside the flue pipe. That's why you want stainless. Stove efficiency is a tricky thing. More is better, to a point. That point is when condensing acid fumes and condensing cresote cause an undesirable amount of corrosion and chimney cleaning costs. A longer chimney pipe gives you a better draft (a good thing) but loses more heat over its length and ought to be operated a bit hotter.Boy, that's a interesting concept - running the really hot air from the little room into the crawl space. Save all that duct work and registers and take advantage of the chimney effect within the old house to draw that air up through the floors. It would work, but. . . efficiency would be less than a stove within the house proper, tending the stove is a frequent thing (but you say the outbuilding is attached). That outbuilding is going to really hot and all combustibles will be very dry within it. (It'll dry towels quicker than your Maytag). I'd go gonzo on the firewall/heat shields. At least one layer of sheetrock on the walls and ceiling (and floor?), maybe two layers of 5/8" (required in all San Francisco houses). Theoretically, if the stove room is below, or at the bottom of, the main house, you could thermosiphon the air and forego the blowers. But the return duct would need to be big. Email me with house dimensions if that's appealing, I could do rough calculations on the duct sizing. -David
*G: You must be some kind of scavanger extraordinarie. If you can score stainless pipe with so many people paying money for scrap stainless just by the pound. What's your concern about triple-wall pipe? I haven't thought about the pros and cons of double- versus triple-wall before. -David
*Brisketbean?I don't think you will be very happy with your proposed stove-in-a-shed. Assuming you have the bucks I would consider an outside wood fired "water stove." Taylor and Hardy are two brand names. There are others. These systems generate hot water that can be pumped to a radiator type water to air heat exchanger in your HVAC system or to some kind of radiant heating system. There are a series of posts somewhere on this page pertaining to these kinds of systems. Some folks think they are good and some are not convinced. Check around and make up your own mind.One thing to remember about wood heat in any form. First you have to find the wood, then you have to cut it, then you have to split it, then you have to load it, then you have to unload it, then you have to stack it, and then, at the worst possible time you have to get up and go out to load up the boiler. You can, of course, buy the wood and pay to have it stacked by your boiler but this is not going to be cheap over time and it will not eliminate those dead of night and middle of the storm trips outside. The only way to make wood heat pay off is to find it, cut it, ------. Good luck!!
*How about pellets?
*G, You're getting a reputation as a scavenger....is it well deserved? I'll have to re-read some of your posts on other threads. On the subject of the stainless steel pipe from the industrial sources: what are the typical thicknesses that you manage to acquire? Can you put a painted finish onto the stainless material? Does anyone know if the galvanized pipe used for agricultural irrigation can be painted so-as to handle a high-temp (900 degree F) application?IMHO, this forum/thread has some real possibilities. I've read some threads in other forums regarding wood-burning topics....not too much thinking or imagination. Let's keep this one going.Brian
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David, I admit it....I'm a notorious scrounger. Kind of a phobia. It takes years and lots of friends and relatives to develop a good network. I get a vision of my next project every time I'm in a salvage yard. The real secret is......Almost all of these facilities sell salvage (usually left over) materials from jobs to their employees first and then to scrapyards etc. You would not believe what you can get for next to nothing at these places. These big mills are in a constant state of repair/replace/re-model...The material is already written off as a job cost. They just want it off the property as soon as possible. Basically, the salvage yards wind up with the cutoffs and other stuff you can throw in a big dumpster.............As for the triple wall pipe, it just gets too hot for my liking. Too close to the limit for starting a fire. I just prefer masonry chimneys for wood burning appliances.
*Brian, This pipe is heavy and tough. The walls are about 1/8" thick. I have made all kinds of things out of it. I don't know why you couldn't sand it and try hi-temp exhaust paint for a custom effect. The pipe is dull and not real smooth, so I don't see why paint wouldn't stick to it. Let your imagination run wild!
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Brisket,
The best part of wood burning things is the radiant heat given off by the thing itself. I think you would be very happy coming home from a 10 degree day to your Vermont Castings stove. I know I have been for the last 15 years. There is nothing better than the quiet warmth of a wood stove with no blower to send drafts all through the house. Have you hugged your woodstove today? I have.
*I agree.....We put one of these in a big, all log hunting lodge and it throws an incredible amount of heat without requiring fans etc. They are also very attractive and durable.
*One of the main reasons in not using mild steel for flues concerns visual inspection. If your pipe from your stove to the flue develops a hole in it,you will notice it immediately. If the inner wallof a triple wall, solid pack or reline (installed to tighter clearances) develops a hole, you will realize it when the fire trucks pull up out front. As for galvanized pipe - it is not used due to toxic outgassing involved with wood stove type temperatures. As for the deal in the shed... Put in an attractive, efficient! woodstove in your home and enjoy the darn thing. Use the shed to store junk.
*Excuse my interruption of this discourse, but when is an outbuilding actually attatched to the primary residence? In my neck of the woods, an outbuilding has always--at least tacitly--meant that other building on the property. If I were to go to the outbuilding, I'd certainly not head for the back of the house. Nay, I'd be off to the "out over there" building.I realise this is akin to picking flys--t out of the pepper: it's all in the details.
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Gentelmen;
Thanks for all of the posts, ideas,0pinions and information. The outbuilding is in the idea stage and will be attached only by ductwork and the building materials are yet to be determined also.
My idea to force hot air into my crawlspace for a radiant heat effect was borrowed from the Deafsmith county solar association, who have done a number of passive solar retroffits forcing hot air under thier crawlspaces mostly from just hotboxes attached to the south sides of thier homes. The main reason for my interest in this is for the more even distribution of heat on the first floor of my cut up
floor plan. I have six rooms and a hallway downstairs
with no room big enough or central enough to place
a woodburner where it would circulate the heat evenly. Anymore ideas on how to enhance circulation
in a cut up house without bells and whistles, I like to keep it simple.
brisketbean
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Bear,
Outgassing involved with galvanized pipe???? Just what are the gases produced???? Are we talking serious chemistry here, or is this an old-wives tale?
Brian
*The galvanizing burns off and causes lung problems. Some are immediate and temporary like shortness of breath from zincosis.-Rob
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I agree with Cavemike, we have both a woodstove and hydronic heated slate-on-slab downstairs floor that is also a passive solar thermal mass, and we have not bothered to hook up the hydronics yet as the stove is fine with no backup heat. (8600 deg/days and -40F min temp here in the Adirondacks, plus free hardwood on our property.)
BUT you might consider making your 'outbuilding' a sauna, with the option of blowing/thermosyphoning the hot air into the crawl space. If you are into saunas, then the excess heat when you and your friends are done in the sauna, can be put into the house. Several of our friends have saunas, two are attached to barns to heat the animals in the coldest weather. I however love my $100 wood-fired hot tub (180 gal stock tank, and homemade heat exchanger - but that's another story.)
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Brian: I've talked to welders (who should always grind off the zinc coated before welding) and they report health problems if they are lazy and just go ahead and weld galvinized metal. The heat vaporizes the zinc and, without excellent ventilation, they breath some in. Apparently, the consumption of milk helps the short-term health problems because the calcium combines with some of the zinc. (That treatment suggestion came from the same welders, NOT a peer-reviewed medical journal). Better yet, don't expose galvinized to high heat. -David
*Dave, Rob,Thanx for your replies, but I guess I am, indeed, looking for the definitive information regarding off-gassing involved with galvanized metal raised to a high temp. Sorry to be so skeptical, but there is a great discrepancy between welding temps (3000+ degrees) and that of a stovepipe (900 degrees, maybe). I think the removal of galvanized surface prior to welding is standard practice, anyway, so as not to contaminate the weld metal....perhaps, that is the reason welders ACTUALLY remove that finish. Do those workers that work in the zinc electroplating industry wear some kind of lung protection as they perform their job? Still looking for the the definitive answer here.Thanx,Brian
*Back in the mid-'70's I had an uninsulated studio on a farm and heated it with wood. Used a long 6" single-wall galvanized sheet metal duct snaked around with several elbows, and a little premanufactured black stove made out of sheet metal. Am not completely sure if the flue was cadmium or zinc plated, I know it didn't have the characteristic crystal pattern that zinz often has when new.The first time I lighted it up and got it real hot the shiney-coating of the flue smoked and turned a dull grey color. The smoke smelled nasty and acrid, but was able to air out the place okay, and the problem never came back. I expected the problem and stayed away the first time. Used the stove for several years. The draft was so good, you could actually gently pull the stove pipe apart 2 or three inches, and see the venturi shaped column of smoke and air go-up the pipe.The flue was never less than 30 degrees from horizontal, good clearances from combustibles were maintained and it was never inspected.The minimum (UMC) clearance from normal combustibles to an unlisted wood stove is 36", and 18" to a single-walled stove pipe if I remember correctly.
*An "outbuilding" is any building outside the main building. It could include outhouses, wood sheds, tool sheds, garden sheds, dog houses, play houses, gazebo's, pump houses, water towers, seperate root cellars, unattached greenhouses, gate houses, guard houses, kiosks, bus shelters, silos, shacks, teepees, tents, yurts, jungle jims, swing sets, watch towers, radio shacks, hen houses, lineman shacks, phone booths, shade structure etc. Whether a typical large barn is considered an outbuilding I'm not sure, I suppose it could be.In some codes, outbuildings not intended for human habitation are exempt or exempt from permit requirements if they are less than 120 square feet. The definition of how that square footage is calculated is another matter for discussion.You can connect an outbuilding with a 2x4 if you want it to be considered "attached".
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RichardB,
I'd like to hear more about the wood fired hot tub!
*There is a commercially available water-heating stove called the Chofu ($600) that can be connected by two 1-1/2" pipes to a galvanized stock tank, for a hot tub. A friend had that set up, and that is where I got the idea.For a heat exchanger I took five 2' sections of used baseboard water heat exchangers (copper with fins) and made a copper manifold of 1-1/2" pipe which connects the baseboard heaters in parallel, with their fins overlapping, in a plane. I used no-lead solder for all the joints. (It will not melt as long as there is water in the heatexchanger)I then made a firebox of 2" thick cinderblock standing on end, and a size so that the heat exchanger fits on the top. An old woodstove door with vent is mortared into the front. I then made a shroud from an old furnace plenum that fits over the heat exchanger (which is tipped up about 6" at one end for the thermosyphon), and has a 5" stovepipe that is 12 ft tall.The high end of the heat exchanger connects to a 1-1/2" automotive radiator hose that attaches to an old sink drain mounted 1/3 of the depth of the stock tank from the top on the side. The low end of the heat exchanger also has a 1-1/2" hose to a sink drain in the bottom of the stock tank, where there is also a T to a plug for draining.A 180 gal stock tank is about 6' long, 2-1/2 ft wide and deep, and about 90$. Perfect for two adults facing each other.My set up will heat the water ~10 DegF/hr if the fire is fed hourly, so it takes about 6 hours to heat up our well water (46F). We do this on the weekends while we bake bread. A piece of 2" foam makes a good cover. We use it every Sunday. I especially like it as we have 2 kids who like to take raucous baths, and they can splash, roll in the snow, and be as crazy as they like. For bathing we get out - soap up - use a pail to rinse, then get in again. We drain it after each use, thus always clean, chlorine free water.Our records - coldest air temp -26F - oldest couple 65+ - most kids at once 7 (plus 1 adult) - longest bath 2 hours 10 min - high water temp 120F (too much for me)BTW Use a thermometer, 100 is too cold for most people, 110 is on the hot side.We scrounged most of the parts, but as I said, a stove is commercially available.Enjoy!Rich
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Richard: Anyone who uses "thermosyphoning" and "homemade heat exchanger" in the same paragraph is my kind of guy. Met my wife on a gourmet backpacking trip which had three rules: formal-dress, bring gourmet food and a toy. I wore slacks, tie, and blazer; used dry ice to keep the ice cream cold; and brought a portable hot tub. Tapped a stream with 120' of garden hose to a lower point where a hole was dug and lined with 10-mil polyethylene sheeting. The water flowed through an 4-core Cadillac radiator with 6 backpacking stoves under it. The raditator was so efficient that, despite red-hot burners underneath, the top surface was cold to the touch.
Like your fin tube, it lasts as long as it has water in it. But I now use a 2-core radiator ($25 at Pick Your Part Junkyard). Maybe 85% efficient instead of 95% but you get a higher outlet temperature. In a 4-core radiator, the upper two cores get almost no heat and only pass cold water through to your pipes. I also switched from 9,000 BTU/hour white gas stoves to a 130,000 BTU/hour propane burner. It gets the snow-camping version to temperature in 45 minutes. Most people I ever got in my 6-foot diameter surplus fiberglass tank home hot tub was 17. But they were very friendly backpackers, no clothing was involved, and very little water remained when they got out.
I assume you burn the wood with excess air to prevent sooting on the fin tube. Such a set up (or a radiator) can be so efficient at recovering almost every BTU that the excess air doesn't hurt you much and excess air makes for less smoke.
Slanting the HX is an important point. It helps establish the thermosyphon in the intended direction and, if you get a little bit of boiling the fin tubes, the "perculator effect" will drive water faster around the loop (as steam bubbles rise up the pipe until they meet cooler water and recondense. Of course the lower the HX is below the hot tub, the better - more flow, more efficient HX, higher maximum fire rate. Congrats on using a long flue pipe. Gives you draft, avoids leaks of smokey air and get the smoke above people's breathing zone. A chimney can be too narrow, too wide, or too short, but never too tall.
Where'd you learn your alternative style of engineering? Drop me a line if you want, [email protected]
-David (Berkeley ChemEng)
*David, G, and Others that consider themselves creative,I've been burning wood for twelve years now, and quite frankly, I detect the wife getting a little tired of the mess that it makes in the most formal room of the house....it's our main source of heat, so there is a significant amount of wood that does enter the space. Anyway, I may be moving the wood-burning operation to a finished room in the basement...my space. I realize that I'll lose some of the heating effect, tho...oh well. I've got a brother-in-law in the logging/firewood business and he provides me with ALL the dry sawdust I could possibly want...by "dry" I mean that his equipment discharges the stuff into a covered horizontal silo and it stays outta the elements. Previously I'd add the stuff (prime hardwood sawdust) to my compost pile and/or use as a mulch in the garden. Lately, I've tried putting about it into those paper shopping bags (about 1/2 cubic foot per bag) from the grocery store and then inserting one of these "logs" into my 1980 vintage Vermont Castings Vigilant ($100 on the used market...price included ALL the dried hickory I could fit into the truck at the time of purchase) atop the other wood each time I charge the stove. They burn wonderfully but must be burned in such a manner that the stuff doesn't smother the fire, ie, I DON'T ever place a bag directly on the coal. Instead, by elevating the "log" above the coals, there is a gradual falling of the sawdust down to combustion zone. I find that what the sawdust lacks in compactness (as compared to actual firewood) it more than makes up for by it's low moisture content and cleanliness. BTW, the 1/2 cubic foot "log" can be inserted into the Vigilant from the top. Anyway, I was thinking about the move into the basement and wondering about adapting that $100 Vigilant for mechanical feeding of the sawdust much as a pellet stove feeds its fuel. I'd postion the stove so as permit a cast-iron auger to feed from a temporary hopper to an optimized combustion zone within the firebox. If this worked, I'd probably build a much larger hopper/storage area outside and make a four-inch penetration thru the rim-joist and plumb allowing for increased gravity to supply the auger. This sure would be easier than making the "logs". Anyone have any thoughts/reservations about this? Any of you scavenger/resourceful types ever come across an auger that might work?Brian
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Brian, I don't have any experience with your concept on a small scale, but I can tell you that my father had a very large sawdust burning stove much like you describe and it worked very well. The key (as you pointed out) is that the sawdust MUST be dry. He had a large hopper (funnel) over the stove and loaded it with a loader. It heated a very large building. He made the whole thing himself and modified it slightly as he used it. We are talking about (sawdust) from a big sawmill, coarse stuff, not something you would get out of your home shop.
I can see you finding an auger behind some old farm implement dealer if you have one in your area. These things come in all shapes and sizes and are used to auger corn and grain.
*Sawdust burning can work well. JK Adams, a furniture factory in Dorset, VT heats their entire set of shops burining sawdust. They are high-tech - with an auger and blower that shoots a fine stream of sawdust into the combustion chamber, kind of like a fuel injector. There is no unburned material, and it is extremely efficient. They have the advantage of fine, dry, oak and maple, saw and sanding dust from the factory. I was told that wet or too course sawdust can clog it. You might enjoy chatting with them about it. Let us know how your system evolves, and good luck!
*A portable hot tub?!?!?! Gee, sell the concept to REI and make a million! Sounds like mucho fun!We actually started with a radiator from a truck, but the fire boiled the water too easily, and eventially the solder melted out and it sprung a leak. Sounds like you have tuned your system better for radiator cores.Your point about the HX being low is critical. I think the flow-rate probably increases linearly as the distance of the HX is lowered. Our Tub is on a pallets that are on a cut on the side of a hill, with the stove below in a smaller, lower, cut.It is also important not to restrict the airflow to the fire too much as you suggest, we tried that and not only got smoke, but also at least a quart of creosote dripping out of the joints of the chimney.What kind of heating rate do you get with your setup (deg/gal/hr)?
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Richard: "Portable" in the broadest sense of the word. The set up weighs about 95 pounds so it has to split up among several hot tubs afficinodos. I've toasted a few radiators, too. They work fine with a pump or positive gravity flow, but the thermosyphon you are relying on creates very low pressures. For a 5 foot vertical run and a 70F to 120F temp rise, you'd get only 0.020 psi or 0.57 inches of water column drving force. So your fin tube (3/4"?) is the ticket. My radiator has a lot of tubes but they're only about 1/4 x 1/8 each which really stinks for handling water at a very low pumping pressure.
My 130,000 BTU/hour burner heats 140 gallons from 35F to 104F in 45 minutes. That's 108,000 BTU captured or 83% efficient, but the measurement are only approximate. I have a 1 hp gasoline-powered pump to move the water fast enough through the radiator.
Do not top off your hot tub before the soakers arrive. The parasistic way to view your guests is as 20 gallons of 98F water each. That much less water that you have to bring up to temperature.
A cheap place to get rigid foam (for insulating the top and bottom) is when docks fall apart. You can find 2 x 2 x 8' hunks of the foam on beach and harbors after a storm sometimes. Saw off the barnacles and make 2-inch planks out the rest. Reduce, reuse, recycle. -David
*Brian: Two thoughts about your proposed saw dust feeding system - one about reliable operation and the other about a labor saving approach.Operation: I'd put the hopper above the stove, if possible. Any auger that has to pull saw dust up against gravity is going to be more prone to clogs and running out of sawdust than one running with gravity. I'd put a conical bottom on a cylinderical hopper and slant a 1 or 1-1/2 inch black iron pipe down to the stove. Extend the upper end of the pipe above the bottom of the hopper. Select a auger wood bit (with a central core) that fits inside the pipe. Milwaukee sells some very substanial entensions for some of their bigger drill bits. Put a gear motor on the upper end (Graingers, 1/40 hp, about $100) to slowly turn that auger. You probably don't need the auger to extend the full length of the pipe. Once the sawdust has cleared the auger, it would slide down the pipe. (Or have the auger move the sawdust down a slope to a vertical pipe for the drop into the stove. Have a large pipe/opening between the hopper and the auger - that's where the sawdust is most likely to "bridge". Or run the auger into the bottom of the hopper itself. The hopper could have a bottom slanting towards the stove with the auger turning at the very bottom of the hopper.There are plastic hopper that hold 40 pounds of dog food and narrow down to a small chute. But metal would be nice above the stove. Having it high would aid in a final drying of the sawdust.Labor saving: I recall a couple of wood stoves in basements in New England which were installed alongside a wood or coal chute. VERY convienent. Back the pickup up to the house, toss the wood down the hole, and then you had your wood pile accessible right alongside the stove. Build a big enough hopper and you could have hundreds of pounds of sawdust and have it self load for days at a time.Let me ponder automatic controls for a bit. Maybe you ought to start a new listing on this topic. Lots of us have access to sawdust. -David
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David - I printed out yor portable-hot-tub idea and gave it to my wife. She thinks you are a genius and is even willing to go winter camping with me now if I set such a rig up. (She has never winter camped with me in 20 years!)
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We should mention that the stock tank is black plastic (not galvanized metal) and not uncomfortable to sit in. Made by Rubermaid, we have one ourselves, and fill it from a hot water bib thru the domestic hot water system, and use it in the summer. Also have washed the dog in it.
I rigged a quick outdoor wood heat system in the mid '70's. Used a recycled 40 gallon gas water heater. Welded flat steel plate over both ends of the vent chamber and attached 3/4" water pipe inlet, outlet, and tp valve fittings through the plugs. Cut a firebox (near bottom) and vent (at top) into what was the pressure vessel. Fired it up with wood scraps, and fed the water thru hoses to the tub inside the house for a temporary bath setup. The temperature/pressure valve later proved its worth when a big cloud of steam erupted from it.
With the insulation left intact it works even better, and although it looks like hell, it worked well enough.
*
I have noticed that all of the double
and triple wall fireplace flue pipes that I have seen are stainless steel on the center piece of pipe. I know that stainless steel is a much harder and more durable material than regular flue
pipe, such as the piece that runs from the woodburner to the wall or cieling but I wonder why and if the inner piece
of the flue pipe has to be stainless steel?
And while I am wondering about fireplace and wood heating things, I am thinking about the feasibility of putting a woodburning stove in an attached outbuilding just large enough
to get setbacks for combustible surfaces and drawing cool air through
a return duct and forcing hot air from the woodburner into the crawl space for a radiant or warm floor system in my
93 year old victorian btu eating home.