Outdoor Wood Furnace Info
Outdoor Furnaces - Manufacturers with NON EPA-Certified Models Only => Home Made => Topic started by: Canuck87 on May 13, 2012, 02:45:47 PM
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Im starting off with a tank I came across for $400. Its not home yet but will be this week. I am going to copy Peatmoss's design. Next I have to go to a scrap yard and try to find the burn chamber and secondary combustion pipe. I am not quite sure how big they have to be in relation to each other. About 12" diameter I think for the secondary combustion. I also have to get some refractory material. Hopefully I will only have to burn every 2 or 3 days in the dead of winter. Heating a 1200 sqft house with basement. Furnace will be inside the shop (36'x32') and have the option to heat that also. Escaped heat will warm the shop some during the winter.... And the summer ??? Trying to decide on what to run for lines underground to the house, maybe pex wrapped in aluminized bubble wrap inside flexible tubing. I'm not sure if I want to spend the money on commercially made line.
Any advice would be appreciated
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That tank looks huge! How may gallons? Very interested in your build, hope you are able to show off your progress. Lots of knowledge on here hopefully some will be willing to share.
Just a thought for you,
I did something similar to what you are thinking with the underground pipe. It works, but some days I wish I would have used the good stuff. I am seeing some heat loss and not sure how long my homemade stuff will last. Also, there are so many variables to these systems, it would be nice know I am wasting minimal effort and expense of gathering wood to heat the the ground!
Looking forward to your progress.
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Holy crap. I can not wait to see this build. I always wanted to be able to burn a truck load of wood truck and all.
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Not sure on the exact dimensions of my tank or the volume. They said it was 5000 gallon but sitting beside a 2500 gallon tank you could tell it was way more than twice the size. I paced it out and I think it is about 24' long with a 8' diameter putting it around 9000 US gallons I will measure it when it arrives this week. Just the steel will add alot of thermal mass. This thing weighs almost 6000lbs. If I fail it will pay for itself at the scrapyard ^-^
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That's a huge project ! 9000 gal will be great. that would run me for 12-14 days. very cool. :thumbup:
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9000 gallons will net you a massive amount of thermal mass. When I finish phase 3 of my project I will be heating a 2500 sqft home and a 3500 sqft shop comfortably with only 1000 gallons. Burning 90 lbs of timber a day once a day. Insulate the hell out of everything to keep efficiency. My underground lines run in 6 inch pvc drain pipe. Pipe is surrounded by a foot of 3/4" clear wash stone buried 48" deep. The gravel prevents water from sitting around the pipes and stealing my heat. I pushed 1" pex through from the house to the burner wrapping the pex lines in those swimming pool "noodles" pushing 4 feet at a time. Tape the hell out of them with duct tape to keep them in place. I bought 100 noodles at wal-fart for $.50 each at the end of summer and figure them to be around R-12 insulation. In 150' of underground run I only lose 5-8 degrees water temp from burner to house during the deepest of frost in Wisconsin.
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Nice score for a tank like that...more like a steal. Just something to consider if you fired that thing every few days to reheat a 60-80deg differential ,hope you hav the day off from work cause it's going to take 6-8hrs to get that thing up with a roaring fire and a constant supply of wood. Myself I think I would use 2000gal of that tank and use a 3000gal insulated reserve tank.
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The heating season is about to start so i'm going to have to actually get to work on this thing. I picked up a 500 Gallon Propane tank from the scrap yard for $300, It weighs about 1200 lbs. I found a good deal on some 4" sch 10 pipe but i'm not sure if it would be thick enough. Right after the secondary combustion chamber where its hottest could be a problem? I cut the opening for the burn chamber in the end of the big tank and next ill take the end off the propane tank for a door. Im going to weld the burn chamber in last because I am planning on welding the fire tubes through the back end of the tank so they are a straight through pipe to clean. The end I plan on building a bolt on access panel where the exhaust will cross over to the tube heading back the other direction.
Part of the reason I want such a big thermal reservoir is to eventually have solar thermal panels heating the tank also. I want to be able to not touch the system for at least 6 months through summer and still have enough domestic hot water and space heating even through cloudy colder weather times.
Anyone have any problems from using thin pipe for fire tube? I'm thinking I should not cheap out and just get some sch 40. I have been researching for a while and have a few ideas/questions.
It seems pretty important to have a minimum return temperature so I plan on adding a thermal valve on the return that will add hot water if needed to keep a minimum of 140f?
I seen a few global hydronic boilers cut open, the return pipe was about 4 feet long 1" dia. drilled every 6 inches with small holes to return the water above the firebox . It was completely corroded away while most other places weren't corroded much at all. Welds looked like they took some abuse also. I may use welding rods with high nickel to make sure they don't get corroded.
What kind of water should I fill it with or does it matter as long as I add corrosion inhibitor. I have hard water at home but it may be possible to fill it only with water run through my softener. Would it be worth it to fill with reverse osmosis? I can get a 1000 gpd R.O. membrane but it would probably take at least 10 days to fill.
For my underground lines I may do the sprayfoam in place wrapped in plastic method that I have read about. I would fill around it with crush and maybe some drainpipe and crush below also. Looking at some commercial lines I realize they don't have much insulation between the pex and the soil.
The tank is 26' long and 8' diameter. I was guessing the weight based on its size but i didn't account for the ends. Lol the hiab I borrowed from work barely managed to lift it onto the trailer.
I will try and add some more pictures this weekend.
Thanks for any advice
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Sch40 would be better if you plan to leave the pipe bare, use the thickest steel plate you can work with for the first face the flame will meet also. I am only using Sch 10 pipe for the 3 I am currently making. I originally chose Sch 40 but after some calculations found that Sch 10 transfers heat much more quickly. I will be coating the front face and first few inches of the pipes with a paint on ceramic heat barrier used in kiln construction for knife making. It's kinda pricey stuff and available on any knife making supplier on the web and there are various manufactures of the product. But I feel the increase in thermal conductivity is worth the extra cost associated, and the barrier will prevent any degradation of the steel surfaces while still transmitting heat in a more controlled manner. Also keep in mind that industrial seem boilers use tubing of .120" thickness or less, which is less than Sch 10 in most cases.
Copper is usually used for a return line to the tank in large systems, especially solar. The copper takes many times longer to react and break down, and galvanic processes within the copper to steel connection also cause an anti corrosive effect.
softened water would be better than tap as it will protect your heat exchangers and lines from internal build up. If you treat the water and test it yearly it will be fine. No need for an expensive system here.
Also make sure your lines have very good drainage all around, drain tile is not necessary though. It just moves the water from one end to another.
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Holy crap with a tank that size have you priced what it is going to cost you for water treatment? My boiler holds 150 gallons and it took nearly a gallon of certified labs water treatment to get it in spec. If I do my math right you could be looking at between $2500.00-$3000.00 for water treatment alone! I would contact a garn rep since they deal with large volumes of water maybe they have a more economical route.
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Your going to do all of that work, and them skimp on line?
Most folks who try to make there own end up having 3.50-4.00/ft in it before they tear it up trying to pull it through.
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I am going to install my own line. I have seen commercially made lines that only have 2" of foam surrounding the lines. A high quality foam has abour R-5/inch which means that line is insulated to R-10 give or take. Thats far less than my house walls are rated and they don't have to retain temperatures near boiling. That is my deciding factor for installing my own. I talked to a local spray foam contractor and he has installed lines sprayed in a trench for mines around this area and apparently it works great. My plan is to have the lines buried with 6" of 2 or 3lb closed cell spray foam on all sides. Also the line will be a steady downhill to the boiler and I was considering putting corrugated drainage pipe underneath the Heat transfer lines.
I have been looking into water treatments. I was worried it was going to be expensive, One call to the local wood boiler company confirmed my suspicions. After that I found a company online that specializes in Corrosion inhibitors. My current plan is to buy boiler treatment in bulk from Accepta. I have a $330 US quote for about 60 litres which is twice what i need for the initial application. From what I have read it is made mostly out of caustic soda which is cheap. I considered just adding a bunch to the tank but that could go horribly wrong. Its not a really big expense for the peace of mind. I have read that Garn uses some sort of cleaner before they add the corrosion inhibitor but considering most people don't add it to their homebuilt boilers I don't think I need it.
I decided to go with the Sch 10 pipe for the tubing but I also got a piece of 5" Sch 40 (10 ft) that I will use immediately after the secondary chamber.
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So today I finally did some work on the boiler. Its been a busy summer but I have some much needed time to work on the boiler now.
I picked up about 80 feet of Sch 10 4" and got an old piece of 5" Sch 40 (10 ft) for the first piece connected after the secondary combustion chamber.
I decided to take the cheap deal on the banged up sch 10. After Peacmar mentioned the fact that commercial boilers use such thin pipe I think sch 10 is enough. I'm sure it will last at least a few years, if it corrodes right through eventually then I guess ill rebuild it then with some better stuff.
A copper cold return line is a very good idea, I have added that to my plan.
The only piece of pipe that I could find at the scrap yard for the secondary was 18" diameter :-\ . I plan to cast my own refractory on the inside which will reduce the ID to about 14"? maybe even 12", I have not decided exactly how thick I will make it.
I started tapering the secondary chamber down to 5" pipe size and cut some elbows to make a 180 back to the face of the boiler. Where the exhaust fan will be. I need some tips for the plasma cutter to finish getting the secondary chamber ready to weld, I am almost half done forming it down to 5". The 5" 180 bend is ready to weld but I have to pick up some 6010 to weld it.
I am anxious to test out the Synchrowave 250 that I picked up Friday.
I have been enclosing my pole barn over the summer also so I have half finished projects all over the place. Finally got a 100 amp service all hooked up so at least I have some power in there now.
Thats where im at now so hopefully i get some more work done tomorrow. Next on the list I think I will start building the fan enclosure and intake pipe. Monday will be a good day after i pick up some plasma cutter parts and welding rods.
Thanks everyone for all the info and comments :thumbup:
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I give you a lot of credit for taking on a project of this scale. Will be fun to watch it progress.
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I'll try to dig up the link to the water treatment I use, I ordered a ton of it a while ago so haven't looked for it since then. At the time it cost about $25 a gallon a one gallon treated 300. But this was based in taking a PH reading and testing nitrates. After that you just do a home test once yearly and add a small amount to adjust. There is also a boiler water treatment company of sorts right in my back yard,(or down the road) in waupaun Wisconsin. It's who Garn uses. I send them my water sample every year for $25 they send me a small concoction to poor in and I'm done. But then there is always the tried and try method that boilers have used for decades, run it to boiling and remove all absorbed oxygen, then never let it get below 140 degrees Fahrenheit. I did this my first two years running year round and the inside still looked like new. Only when the AC worked too hard to expel the hear the boiler was bringing into the house for hot water did I finally give in, treat it, and shut it down for the summer. But record summer highs will have that effect I guess....
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I have put lots of time into it this week and its coming along well. The primary and secondary are welded together and the intake and exhaust passes are welded in. I made up a fan rotor for the exhaust but it wasn't too pretty. Formed a fan enclosure and mount for the motor also. Took a while to line up the fan so the rotor didn't drag anywhere inside. I made the clearances pretty tight because I wanted it to have a good amount of suction. 10" diameter with 6 curved blades. I don't think I ended up taking a picture of it though.
The fan sucks through the burn chamber and blows out the back with a good amount of force though. I was concerned it might not be enough volume to give a strong burn. I Still have to mount and seal the door to see the true amount of air going through. It will add another 26' of 4" on the intake side. My fan only rotates at 1072 rpm though so I can change the motor if it is not enough.
The door is the next on the list and then sealing up the open ports and entry hatch on top. I am going to put a 500 gallon tank above the boiler as a separate expansion tank and am considering putting a tidy tank cap or something similar on it. would hold +2psi and -0.25psi. To try and limit the amount of oxygen entering the tank. If i can let it pressure up to 5psi and not have it vent any air i would be happy.
So far I've burned through about 15 lbs of rods. Mostly on the 1/2" fillet weld around the burn chamber. Also welding the tapered end of the secondary was a lot of work.
Won't be too long now and ill be moving it into place insulating and trenching.
I just ordered a brazed plate heat exchanger and a water to air for the furnace plenum.
The secondary I lined with a mix of furnace cement and vermiculite but i am planning on putting a layer of 1" firebrick inside of that. The vermiculite layer should give it lots of insulation, also helped make the diameter a little smaller.
I am running some tubing along the bottom of the firebox to feed air to the secondary and will put a crude gate valve to control the ratio between the primary and secondary air. Maybe later could be controlled by a servo and oxygen sensor. I will put a port in front of the secondary to give me the option to thread in a sensor also.
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I've taken a few extended weekend trips recently but have managed to get most everything wrapped up. I welded all ports on top shut except one 2" valve on one end. All the welding inside is done, I just have to weld a sealed hatch cover on top to close the 2x2 access hole. The door latch is mostly built but I still need a spring before I can bolt it on. I have door seal rope and will weld on some tubing to hold it today. (4) 5 Gallon pails of pour in place foam arrived the other day along with the heat exchanger for the plenum and a brazed plate to go on the tank. This weekend or next week I am getting a mini hoe to come do a ton of trenching. I am digging down to the footing around about 3/4 of the house basement to install foam insulation and some big-O drain tubing. Moving the tank is about as tough as expected but I think today I will have it moved into its new home in the pole barn. It has been snowing and down to -10c at night, hoping to get this all wrapped up really soon.
One last problem is trying to find large diameter pex at a reasonable price, or even at all. I am going to run a glycol loop with oxygen barrier pex but I need at least 1 1/4 to not restrict the flow over the 150' to the furnace room. I heard of some installs done with sch40 steel tubing. I can get enough 1 1/2 for $600. Thats at least half the price that smaller pex will cost me. Has anyone used or heard of doing this? If it is sealed in foam and has glycol on the inside I can't see it corroding at all really.
Pictures coming soon, been busy and not too much time to post
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If its a closed system you could use steel tubing, but if its an OPEN system which I suspect it is - you have to use Brass, Copper, PEX, Bronze or Stainless components otherwise the oxygen will go after the weakest Ferrous link and then you get to replace/replumb in a year or two..
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Here are some pictures of my recent progress. The shaft I turned is the center pin for my hinge, Its stainless steel shaft off of a boat. I Got a picture of the fan rotor I made also, I faced and rounded it off with the lathe later. It fit into the housing very nicely but I haven't started it up since the door latch and seal were added to check total airflow. I welded some 3/8 erw tubing around the firebox opening and Zipped a slit all around it. Pried it open and stuffed in some 3/4" rope seal. Seems like it should work well. The latch I put on is a toggle clamp for $12 which may be swapped out later. I added some more support on the hinge after that photo, wasn't as sturdy as I wanted. I have plans for a loading lift also but that will come after this thing is fired up.
I ended up ordering some 1 1/2 barrier pex for the loop to house, 4000km later ill have it here. At least I won't have to worry much about flow loss with some system expansion in the future. I have a big water to water heat exchanger that the tank will circulate through. After that there will be a closed 50% glycol loop run to the house Everything will be oxygen barrier. This eliminates any large volume of water from getting into the house ;) Some pictures of my foam also.
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Well I have finished up almost everything on the boiler and filled it with water. I built 2x4 walls around it and covered them with aluminized bubble wrap as a vapor barrier and radiant barrier. The wrap follows the curve of the tank underneath with a 10" space between the two that I blew in with cellulose insulation. The top of the tank isn't completely covered yet because i ran out of insulation. There was one leak in my welding coming from one of the ports on the propane tank that makes up the burn chamber. It was easy to access though and i welded it from the inside. The plumbing going into the house and underground line is all done also. Just have to bolt on the Primary circulator and solder a few copper fittings.
I started it up and found out there was not enough airflow. The fan was of poor design :bag: lol Also the motor was not fast enough. My Dad had a 3/4 hp 3450 rpm motor laying around so that is now on there and i build a much stronger fan that had some real effort put into it. I balanced it by welding on the lighter side when it was held by two bearings. Also changed from direct drive to belt drive. It is easier to remove now and I can adjust the rpm if i need to. Currently turning at about 4000 rpm.
So thats where I am currently at. once i get the tank up to temperature I will fill the loop that runs underground and through the house then turn on the pumps.
I have burned two half loads of wood in it so far though (second one is still going)
My problem now is that it continues to smoke even when the fire seems to be going well.
I am not sure if it is because the entire tank is still very cold or if there is a design flaw.
The one thing i made quite different is the secondary chamber air source.
There is 4" coming from the back of the tank to the front and it runs into an air collar that covers the bottom half of the primary. There are holes cut to let air into the front of the firebox and also a bit of a manifold that directs air through two thin wall 2" tubes that lead through the coalbed and end in front of the secondary chamber.
When I open the door the fire does pick up a bit and then i see flames being pulled through the secondary but it doesn't appear to really be burning there and it is still smoking.
The first load I tested with was mostly kiln dried wood scraps and other waste wood. I thought it was burning too fast but the current load of wood were some well seasoned big splits. I left them quite big to try and make the whole load burn slower.
It is still blowing smoke though. I can adjust the air from the primary to the secondary but it doesn't seem to make a difference.
Anyone have any ideas on what could be causing it?
I thought it could be that the intake air isn't heated enough because the whole tank is cold but i'm not sure.
When the door is open the fire seems to be burning quite cleanly but it is still pumping out smoke.
Thanks in advance for any advice :)
I will post a bunch of pictures once I get the plumbing finished and the insulation done.
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I put a few 4' 10" dia. logs in there and it started to burn really clean, also realized most of the 'smoke' coming out before was steam, Duh. There is a lot of steam though.
I haven't really seen the secondary burning itself though.
I think cold water is or was slowing it down. It is at about 80f right now, there was ice in it when i first lit it.
I think ill get the insulation finished tomorrow and cover it up in a few days.
Will be off the oil forever in a day or two ;D
I'm going to add a few links here to some info I have found helpful
Thermal mass info and cool calculator http://hillsideenergy.com/thermal_storage.htm (http://hillsideenergy.com/thermal_storage.htm)
Dew point of Flue gases. http://www.engineeringtoolbox.com/dew-point-flue-gases-d_1583.html (http://www.engineeringtoolbox.com/dew-point-flue-gases-d_1583.html)
Residential pex plumbing book Pex dimensions
Flow loss up to 2" tons of other info http://www.scribd.com/doc/50559573/21/#Table-3-1-%E2%80%93-PEX-Pipe-Dimensions (http://www.scribd.com/doc/50559573/21/#Table-3-1-%E2%80%93-PEX-Pipe-Dimensions)
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Canuck, nice build! curious how it is working on your first run?
can you explain or post a picture of how your intake air is pre heated before entering the burn chamber? I understand the garn circulates air around a collar at the front of the firebox but have never seen one in person.
Thanks
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Well I loaded it up on friday afternoon in the first pic. Refilled it around 10 a little more than the first time and let it burn out overnight. I shut the fan off around 9am and it was at 183F, the fire was still burning a little. exhaust temp at the fan was still over 200F. The highest i've seen it while burning was around 450 i think. I have been consuming around 10F every 24 hrs. temp around here has be around freezing during the day and down the -10C the coldest overnight. I wanted to put a water meter on during the fill but it never happened. I am estimating around 8500 gallons US. in the tank now. Works out to be around 30,000 btu average load. Once I get the pressure relief valve i ordered im going to bring it up to 5 or 6 psi. Water would boil at about 225F so i could possibly heat to 210. I may just leave it unpressurized though.
I have it on a on/off switch right for the blower right now so no auto shutoff. There are two pid's coming from china for me but not for a while. I've been measuring temps with my cheap IR temp gun and the temp changes on different metals, hard to get a good measurement. I have one pid to install temporary to display the tank temp as soon as i get the thermocouple in the mail.
Im going to mount the Pid's just above the indicator lights on the panel. One will read Water temp and will be the high limit control on the blower. set at 200F i think.
The second Pid will read the exhaust temp at the fan and trip a relay when it drops below set limit 250F or something. There is a green push button switch that will power a relay to turn the blower circuit on. It will power the blower until the pid sees the exhaust temp rise above my set point. The pid will turn on a relay that switches power from the green push button circuit and turns it directly to the fan. The relay holding the push button will lose power and release so when the exhaust temp drops its pid relay will switch power back to the push button which will be ready for the next "start cycle"
If anyone is interested i can draw a schematic.
I will be happy when that is all finished up. I still need to cover up all the sides of the boiler and hook up my sidearm. The basement is unfinished but I have to pry 1x6's off the ceiling to run the pex. I am planning on running a third Pid to control the zone pump to the sidearm. Hey, at 15$ a piece one day ill have those things installed everywhere. ;D
3rth pic is of a log about 24" long and more than 30" dia. that i wrestled in there.
Last pic is of my control panel. I still need a couple relays and 24vac transformer to power them. The scrapyard should have some old furnaces that may have them.
I dind't take any pictures for some reason when i insulated my line ???
I made a trench out of blue xps and laid the pex in place then poured in expanding foam to seal them. I used 8 foot pieces and left a gap between each as i went. The pex ran in one window and encased in foam ran out the back door. It was too cold for the foam outside and there was no room in the bottom of a 5' trench to work. I filled in the gaps on a warm day with a blowdrier for added heat.
The 2" foam board to enclose the lines would have worked well installing it with spray foam in a trench though.
Ill take some pictures of my inside manifold sometime here also.
It has one circulator pump and 3 zone valves. thermostat is hooked the the zone valve and an endswitch turns the circulator on.
Well, ill post some more pics and stuff as i get more completed.
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Glad to see you got it up & running looks real good. I wish i had that much storage. here's a link to the water treatment i used.
http://www.ebay.com/itm/Outdoor-Boiler-Stove-Anti-Corrosion-Chemical-Treatment-/220694191436?pt=LH_DefaultDomain_0&var=&hash=item3362661d4c (http://www.ebay.com/itm/Outdoor-Boiler-Stove-Anti-Corrosion-Chemical-Treatment-/220694191436?pt=LH_DefaultDomain_0&var=&hash=item3362661d4c)
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So today I finally did some work on the boiler. Its been a busy summer but I have some much needed time to work on the boiler now.
I picked up about 80 feet of Sch 10 4" and got an old piece of 5" Sch 40 (10 ft) for the first piece connected after the secondary combustion chamber.
I decided to take the cheap deal on the banged up sch 10. After Peacmar mentioned the fact that commercial boilers use such thin pipe I think sch 10 is enough. I'm sure it will last at least a few years, if it corrodes right through eventually then I guess ill rebuild it then with some better stuff.
A copper cold return line is a very good idea, I have added that to my plan.
The only piece of pipe that I could find at the scrap yard for the secondary was 18" diameter :-\ . I plan to cast my own refractory on the inside which will reduce the ID to about 14"? maybe even 12", I have not decided exactly how thick I will make it.
I started tapering the secondary chamber down to 5" pipe size and cut some elbows to make a 180 back to the face of the boiler. Where the exhaust fan will be. I need some tips for the plasma cutter to finish getting the secondary chamber ready to weld, I am almost half done forming it down to 5". The 5" 180 bend is ready to weld but I have to pick up some 6010 to weld it.
I am anxious to test out the Synchrowave 250 that I picked up Friday.
I have been enclosing my pole barn over the summer also so I have half finished projects all over the place. Finally got a 100 amp service all hooked up so at least I have some power in there now.
Thats where im at now so hopefully i get some more work done tomorrow. Next on the list I think I will start building the fan enclosure and intake pipe. Monday will be a good day after i pick up some plasma cutter parts and welding rods.
Thanks everyone for all the info and comments :thumbup:
What type of refactory did you use for your secondary chamber? How did it work out??
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I used super 3000 refractory cement mixed with vermiculite, it was about 2 1/2" thick. Then I lined the inside of that with firebrick to make the chamber a bit smaller and more durable.It seems to be holding together fairly well.
I kind of tried to copy the design some people have used to make forges.
If I found a place that would make a liner that I could have bought I probably would have went with that.
It was a bit of a pain to make and refractory cement isn't that cheap
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I hope that holds up for you. I've tryed castable refactory for a aluminum melting furnace and have never been impressed with the results. It seems like I'm always chasing cracks in the lining and I know curing (or driving the water out) in the key to having it come out good. Garn and most people building these style wood furnaces are buying custom premolded ceramic inserts for the secondary chamber.