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We plan to use a wood fired boiler to heat a radiant heated floor system. I am interested in real-life experience with these, both inside and outside types. Specifically I would like to know which of the many outdoor types you feel is the best to get and why. And what is the downside to using this type of boiler, other than the obvious of the hand work involved in dealing with wood. Sacie
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Replies
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Sacie: One possible mismatch could occur if the wood-fired "boiler" is designed to actually boil water or to produce high temp (180F) water. One of the advantages of radiant floor heating is that you use low temp water (80-110F) and therefore get a higher efficiency out of your water heater, if it is one that can handle the lower temperatures. You can avoid problems with the readiant slab being too hot (hear about those problems in Rick L's post about cracking gypcrete) by using a mixing valve to mixi hot boiler water with colder water returning from the slab.
But if you operate any heater colder than it wants to be, you can get flue gasses condensing in the flue pipe. -David
It can be tempting to get a big firebox (save a lot of work sawing if your wood-burner takes 5-foot logs) but in a modern, insulated house, it's easy to have too much stove
*Sacie, To add to what David said, One of the problems you have with wood fired boilers is that you really don't have much control over the water temperature or heat output like you do in a gas or oil fired unit. Therefore you have to provide one circuit that can run "wild" and dump heat all the time. You can't just stop the flow of water through the unit because it will immediately boil. What we do in our shops is use the mixing valves as David suggests to allow lower temperature water to flow to the floor tubing and then dump the rest into regular heaters in other areas where an exact temperature is not important. You can't run low temperature water through the boiler because creosote condensation will form on the water jacket right inside the boiler. Unless you can pay a lot of attention to this system, I would try another source of heat for home heating purposes.
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Interesting the suggestion that wood fired boilers could send out water too hot; however the half dozen I am looking at all say they are suitable for this purpose. We like the idea of using this heat source because we have nearly 80 acres of woods. We're building a tight, well insulated house BTW and a free heat source, (in addition to the sun)is my idea of a perfect combination. We in a 5000 degree heating day here which I'm told is too warm for a masonry stove, another consideration. Sacie
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Sacie, It's 10 below zero outside and I'm sitting in front of my big, south facing picture window after throwing another log on the fire....so I know what you're saying! I'm just trying to point out that these systems are tricky to use for home heating. They require a lot of planning and attention if they are to work right. Any wood boiler can do what you want to do if set up properly, but you will probably experience more temperature variations in the home than you would with a gas or oil fired system. There are also many different types of boilers, so do your homework before jumping in! Good Luck.......
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Sacie,
We have used a wood-fired boiler in conjunction with our oil-fired boiler for about 5 years and are very happy with it. We have no radiant floor heat, just regular old radiators.
Our boiler set-up is simple: the wood-fired boiler heats water in it's jacket and sends it in a loop to the oil furnace. The oil-furnace circulators are responsible for sending heat to the house. THe wood-fired system creates a larger reserve. Domestic hot water is REALLY HOT, and since the wood-stove circulator going all the time, some hot water is forced through the rest of the system resulting in radiators that are always just a little bit warm. THe house is always more comfortable and temperature fluctuations are smaller.
We also have a source of 'free' wood that we wanted to be able to use. THe whole set up could use some improvements, but it works well enough just the way it is that we haven't felt compelled to mess with it yet.
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Bill: If the REALLY HOT Domestic hot water bothers you (scald hazard, little kids around, hard to adjust showers and sinks to the desired temperature) you can install a mixing (or "tempering") valve before the DHW leaves the water heater and heads for the plumbing fixtures. They're about $40-65 and are adjustable form 105-140F. In a conventional water heater setup, they can be used to maintain safety and convenience in the house while cranking the water heater set point up to create more capacity. -David
*Sacie,Richards Heating and Cooling in Hardy, Arkansas is a dealer for the Taylor Hot Water Furnace and I think they may have been a Hardy dealer at one time. I know that they sell and install a lot of these kind of out side wood burning units. Their number is (870) 856-3853. Possible source of information.
*FredL, did you know Monitor makes a hot water heater. wonder how it would work with radiant heat????.
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Much as I very much appreciate the conradictory advice I read on this subject, I remain interested in seeing something from folks who have a wood-fired boiler AND are using it for a radiant floor. And Fred, wouldn't that mixing valve solve over heating problems? I didn't think 5000HDD was 'mild' either. After all this is Kansas and the wind is blowing to -40 tonight. Sacie
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Sacie: That mixing valve would solve the overheating problem as far as the slab is concerned. When the thermostat didn't want any more heat, the pump or control valve for that zone would turn off and the slab would not get any more heat.
But if you've got a firebox full of wood at that time, where is the heat going to go? Into the water jacket of the wood-fired heater until the pressure/temperature safety valve blows hot water out somewhere. So you will want to configure it so that the floors do continue to take heat from the wood-fired heater or have another place to dump heat (automotive radiator and fan in the garage?) that has a lower priority than the house. (i.e. when the house wants heat, it gets it. But when the house is happy and the heater is still putting out, heat dumps to the garage.)
I'm putting a radiant slab into my house in Kenai, Alaska (9,000 HDD, so Kansas sounds mild to me, but it's all relative). I first thought, "Well of course we'll heat primarily with wood - we're on 13 wooded acres and there's lots of beetle-killed spruce that's a fire hazard and needs to be gotten rid of anyway. But our heating bill on natural gas would only be about $300/year (at $0.38/therm) and then the $3,000 cost of wood stove, chimney, hearth, etc. doesn't have a great payback. We'll still do it as a focus to the living room and because in a radiant slab heated house there's no very warm place to go when you get chilled outside. But I better enjoy the chainsawing and splitting because I won't be "earning" much per cord. -David
*David, That is an excellent overall explanation of how this all works and the cost/benefit aspect of it. I have a hunch some people still will have to find this out for themselves though ! By the way, we use the commercial version of your fan and radiator system ( Modine) hanging radiators. I can usually find them when they are tearing down an old commercial building somewhere and they make excellent heaters to hang in the garage or shop. We have very warm cars and trucks around here.........
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David, your explanation makes eminent sense to me. Now, before I completely abandon my idea for 'free' heat, I am wondering if there isn't some way this could be worked out scientifically, or engineeringly. We do have a large workshop that will need to be heated. Surely there is a way to figure out if a wood fired boiler would blow the system or not? ie a good analysis of heating needs such as HVAC folks are supposed to do, but rarely do? (And I wish that we had access to inexpensive natural gas too; our best alternative is propane that has ranged in price between $1.20/gal to the current .60/gal) Many thanks for all of your replies. Just help me with this last one. Sacie
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My understanding is that "water stoves" use a sealed combustion chamber. The fire "idles" until a call for heat is sent by the thermostat. At that time a blower engages and the fire is brought up to heat the water. When the water is hot (not necessarily boiling) a circulation pump comes on. I would not worry about wasted fuel or BTUs being pumped out. Not an issue. I would not be concerned about tempering the water temperature. It will circulate at whatever temerature is set for the system. Closed loop. Most systems transfer heat via a water to air "radiator" in the HVAC system. However, it should work just fine in a radiant floor. You can use a tank and coil style water to water heat exchanger for domestic hot water. Suggest you contact dealers and manufactures for contacts to people who have the kind of application you are planning. Don't give up just yet.
*Be careful that the water you send to the radiant floor tubing doesn't exceed its tolerances (150-180F, depending on type). -David
*G. LaLonde: I'd love to score a few of those fan-equipped radiatiors - really handy for large spaces. (And we have unmetered city water at 40F so we have free AC for those few hot days each year).On an environmental engineering project, someone had spec'd a 200,000 BTU/hour heat exchanger with one-off drawings and an attached bid from a fab shop for $5,000. I went to Pick Your Part "Auto recycling center" a.k.a. junkyard and bought a 4-core Cadillac radiator for $25.99. Worked great (good to more than 240F and 15 psig). Handled up to 600,000 BTU/hour. It's had to beat Detriot for cheap mass production. -David
*Sacie: I'm agonizing over that same point - free wood and how can I make use of it in a way that makes sense. It will probably be a longer term project - need to get the house finished first. But I'm dreaming of a LARGE garage/wood shop/ boat house/ project test bed building. I know several home sales here in Alaska made on the basis of the great shop, screw the house.This is still very preliminary in my head but something like: Large wood-burning furace maybe made from an old oil or propane tank to take 5 to 6-foot logs. Huge water tank (5,000 gallons) to hold the heat from a 500-pound charge of wood. Fire it once, capture 4,000,000 BTUs and then circulate that water for the house, shop or (and this is cool) radiant driveway snow melting. Should last for days. Gives me a place to get rid of that beetle-killed spruce and there's minimal cutting and splitting.For cheap water tanks: surplus PE agricultural tanks; site-built circular plywood with 16-inch center insulated stud wall; or sub-surface. Dig a 100-cubic yard hole, line it with 80-mil PE, fill it with sand, and rely on the 30% porsity to provide the storage of 5,000 gallons of water. -David
*Steve, I believe the closest anyone came to making a system that functioned as you describe was the pellet stove. They used a manufactured wood pellet with uniform moisture and burning characteristics. They quit making them some time ago because they were troublesome and not very cost effective.They want to use home grown firewood which, as we all know, is not very consistent in its burning qualities. I have seen many variations of automatic fans and draft doors. They certainly can make a fire throw more heat but they aren't good at making it "idle" (smolder) If you have an aquastat that turns on a pump when the boiler heats up....then what happens?? Does it send out water at 120-140-160-180-200 degrees?? If you have a radiant floor heating system, this is certainly something to be concerned about. Very hot water not only makes the slab very uncomfortable, it also will damage the tubing and possibly the concrete. You have a very small amount of water involved in a home heating system and it doesn't take much to heat it. Then what happens when the room thermostat shuts your pump off and the fire has not "idled" down completely? Does it blow the P/R valve on the boiler like a steam whistle? Gas or oil fired systems may not run for hours after the slab is warmed. Do you have any ideas for making a fire "idle" for hours without causing problems?David gave a very good explanation of how to hook a system up. You do not need to worry about blasting hot water out of your boiler as long as you have a zone where you can dump excess hot water and you can keep your garage or shop or whatever warm at the same time........
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Steve, thanks for your encouragement and I wonder if there might be a misunderstanding about what we are talking about here, so since this horse isn't yet dead I want to keep on beating it a bit. Do those of you who have suggested this isn't a good idea understand that I'm not talking about making this boiler myself? I have literature from a bunch of sources (Wood Master, Central Boiler, Heatmor, Homestead, Hardy, Lynndale and the cadillac of them all, Tarm --which is indoor and the most expensive by nearly twice). ALL of them claim use for a radiant floor system. The stoves range in BTU output and have pressure releasing valves. I asked this list about this system simply because I have too many choices. I have yet to talk to anyone who actually uses one and though I suppose I can get the various brands to put me in touch with folks who use the boilers, I thought you all would be more objective and might give me better advice. Armed now with questions I will approach the suppliers. All of which is NOT to say that I am yet sold on wood fired boilers. I want a good system that works.
*Sacie, My final thought on this is that....We are more objective and we did give you better advice!
*Sacie,Do you currently have any other unit in your your house supplying hot water? One reason our system works is that there was an existing oil-fired unit and radiators in place. I have never had our wood-fired boiler overheat, probably since the oil furnace and radiators are always available to absorb excess heat. There is a thermostat on the wood unit that will start the circulators and dump hot water to the radiators if the wood boiler overheats, but so far, it has never happened. I still imagine that you would need something to prevent overheated water from circulating to your floor, or you would burn your feet as Fred points out.
*Bill, We don't have anything yet. This is for new construction. There is an existing large new garage on the property that I plan to convert to a workshop and which will need heat. I figure I can pipe to that and install radiators or some such thing there. Also will use boiler for heating DHW. Our floor plan is for a long, but not big house, with a totally sep. bedroom. I could pipe to that small building too. Seems that if I size the boiler right I should be able to cover all these areas and get what I need and not overheat. Again these things have pressure valves on them and heat regulators AND I could add an outdoor Japanese style tub too. Still, I will talk to the folks who make these and see what is what. thanks for your interest. Sacie
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Maybe I am misreading at the HS Tarm Website. As I understand it, their boilers are "wood gasification" boilers. This is significant in that tye gasification and burning are in two seperate areas. In an open fire the gasification and combustion happen all at once. Anyways, they say they start and stop the combustion. It is specifically mentioned in the verbage.
I was considering an outdoor (or in an outbuilding) application to heat three buildings on our property, to keep the mess outside.
-Rob
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Rob, I think you have to follow the whole line of thinking here from the original question down. The original question was about heating a radiant floor slab (ONLY) . Later information revealed this to be a modest home in Kansas.
Unless you are a real nature buff and love cutting wood, feeding a wood stove and hauling ashes etc. this does not make any sense. I live in a 5200 sq. ft. home up North with a combination slab/radiator natural gas hydronic system and I've never paid more than $450.00 a year in heating bills. I have installed dozens of these systems since the early 1970'S and the only people who haven't converted over to gas or oil are the sawmills or loggers who are trying to get rid of wood.
I don't believe ANY type of wood boiler ,and there are many, is practical for heating just a small home. Later in the discussion the plan changed to heating several other areas, domestic hot water and (a hot tub). Now you are getting into an area where it is at least mechanically practical to use a system if your heart is really set on it and you have the time and energy to fuss with it.
I can tell you this...This whole setup will not be worth the expense or trouble if you can't find someone with a thorough knowledge of how these systems operate.
Where is all the firewood going to come from. We used at least 10-15 full cords of hardwood in a 7 month heating season. If you are new at woodcutting, this is a lot of wood to cut up and haul, and it gets old FAST.
Just a few more points to consider before you spend an extra $10,000 on something like this......
*Rob, Between what you read on this list and what you might get privately, I suggest you pursue the wood fired boiler. The outdoor types cost $3,000-$5,000 depending on the BTUs you need and many take large (4 foot logs). Some people like us like the 'work' of cutting, hauling etc. I've done it off and on for 12 years and still find it work I enjoy. I would definitely have a back up heat source though. In our area we can't get natural gas and electric is high and propane, while low just now was exactly twice the price three years ago. A more important aspect of heating any building is to build well and tight and then you won't have to use so much fuel to warm it. I would be interested in knowing what you come up with should you decide to pursue this, since I'm still in the finding out stage too. Sacie
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G. LaLonde:
Here in Virginia the stores still stock pellet stoves of the free standing or insert type and the pellets in 40# bags.
One year at our State Fair I saw a stove burning dried corn kernels.
None of these were boilers.
Frank
*Sacie, The $10,000 figure was for the boiler, new outdoor boiler house and storage, underground insulated piping , wiring etc. and then hiring someone to install all of this for you.... You could take that money and make a couple grand by throwing darts at a copy of the Wall Street Journal and picking something....Would you settle for a nice Vermont Castings stove to warm your feet?? Don't give up on woodburning...I love it! But step back and take a practical look at your home heating needs,especially if you intend to use radiant heat in the floor....
*Frank, Interesting ! We used to sell a lot of scrap wood material and low quality timber to a company that made pellet stoves and made the pellets. I always thought they were kind of neat. My father had a huge version that he made himself, and used it to boil maple sap. The market for both the stoves and pellets dried up as homes and other buildings became more energy efficient and fuel prices started to decline. I hadn't seen or heard anything about them in years. Perhaps the wood pellet market was overtaken by the corn pellet industry!
*After the first pioneers crossing the plains used up all the trees and bushes, the latter travelers used the dried cow flops from the early wagon trains for their cooking fires. -David
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G La Monde, As a newcomer to this list I know I'm sticking my foot in my mouth and asking for it but I can't help but reply again. FYI, wood fired boilers come with their own little house, some are stainless steel. 'Plumbing' these is not terribly expensive and yes I want a 'real' wood stove too. That plus we do a whole lot of our own work when we build,--- and I take the Wall St J. for other reasons. (ie still pursuing the possibility and I'll let you know a year or two from now how it all works out). Sacie
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We plan to use a wood fired boiler to heat a radiant heated floor system. I am interested in real-life experience with these, both inside and outside types. Specifically I would like to know which of the many outdoor types you feel is the best to get and why. And what is the downside to using this type of boiler, other than the obvious of the hand work involved in dealing with wood. Sacie
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Sacie,
I too enjoy the "work" of cutting wood, and I actually miss it. I also miss bailing hay too so perhaps I am strange.
I have heard all kinds of arguments to not burning wood because it is "such a lot of work." These statements usually come from people who by my estimation are lazy.
I like the argument that instead of cutting and splitting wood "you should just get a part time job and use that money to pay your gas bill." My answer is that I will take any job that allows me to work in my spare time, has no boss, does not deal with people, allows my children to work with me, and counts as quality time with loved ones because I can them to work with me and converse about whatever I like.
Has anyone ever considered the therapeutic effects of this type of activity? How many people pay thousands each year to run in place on a treadmill or endlessly climb steps without getting anywhere? All of this to try and counter the effects of their otherwise sedentary lives.
Aside from the free heat, why shouldn't I use the deadfall wood from the 500+ acres behind my house? I already have the saws the hammers, the tractor, the loader, the trailer, etc. This wood will otherwise rot, get washed into the stream, and end up as sediment in Lake Ontario.
I guess what it comes down to is I enjoy being outdoors, regardless of the weather, and maybe that id why it seems rational to me.
-Rob