Outside furnace

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I am building a furnace to heat a house that is outside going to burn coal and wood. The main box is going to be made out of 3/8 plate 24" wide 24" tall and 36" long the outer skin is going to be 14 gauge sheet it will have 2 blowers on it one to blow in the furnace and one to blow the heat in the house I think I gotta good plan on this build but any advise would help thanks
Reply:This ought to be good.  You didn't build that.'85 Miller AEAD-200LE
Reply:They are sold commercially around here. The brand name is "Wood Doctor".shaped like a small building and last for years.Brian
Reply:Originally Posted by BrianCThey are sold commercially around here. The brand name is "Wood Doctor".shaped like a small building and last for years.Brian
Reply:I've NEVER seen a commercially produced outdoor forced air wood furnace.  Only wood boilers for hydronic heating or a heat exchanger in a standard furnace plenum.You didn't build that.'85 Miller AEAD-200LE
Reply:My plan is to push the air from the box into the house then have it pushed back into the box so it will have two air ducts on it one out and one return Just got done cutting the 3/8 plateMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:just got done cutting the plate Attached ImagesMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:Originally Posted by beck549My plan is to push the air from the box into the house then have it pushed back into the box so it will have two air ducts on it one out and one return Just got done cutting the 3/8 plate
Reply:Originally Posted by anickodeyou should probably plan for pressure vessel quality welds on that firebox...  A carbon monoxide leak into the air jacket could possibly result in a very bad winter.
Reply:Originally Posted by AndyABlow air into the building so that it's very slightly pressurized.  Duct the firebox air inlet to the outside of the building.  The firebox exhaust should be connected to a chimney.  This way the firebox is slightly lower pressure than the building.  Any leaks (or rust holes later on) will push air into the firebox rather than leak smoke or carbon monoxide.
Reply:The moment you start DIY messing with cross flow heat exchangers using air as the heating medium, you invalidate your insurance policy.All of the hot air gas heaters in OZ that use the principle of a two layer hot box design have an air sensor that senses for any exhaust fumes from burnt gas should the fire box develop a hole and leak fumes to the incoming air.The sensor cuts the gas off and locks out the controls and gives a LED flashing warning code on the control board to indicate the fault present.My first Vulcan gas heater firebox developed a hole and had to be replaced, luckily withing the 3 year warranty period, but it did the same again 4 years later....exhaust fume sensor locked the system out.Ian.
Reply:You have internet but no natural gas?Welding/Fab Pics: www.UtahWeld.com
Reply:I have internet, but no natural gas. Well... there is natural gas, but right now it's locked in some rock some 8000' below my farm. Hopefully I'll be able to heat with gas in a few years.  Until then, I'm still splitting piles of wood.
Reply:No real need for 3/8 plate fire box in a hot air system. That being said it can't hurt.I converted a Fawcett Hot air wood furnace to an outside unit to heat my garage, works excellent, no blower for the fire, just for the air. The fire box is only like 16 gauge.Not to be a downer but check with your home owners ins. IF I was going to have it heat my house, I would install some fire dampers in the heat ducts.Insulation will be a key factor in keeping the fire burning for longer times.One thing to remember is you can't store air, if the temp warms up out, the blower will still have to cycle on as the fire continues to burn. A good dampening control is key to slow the fire down. The less bends in the duct the better, the insulation can be marginal as the air doesn't stay in the duct long enough to have adverse affects. My ducts are insulated triple wall pipe with an inside diameter of 10".I insulated my chimney stack to help cut down on creosote, works pretty well.Here are a couple of pics of my setup.I used an inner and an outer layer of a product called ReflectexGood luck and keep us posted!
Reply:Originally Posted by anickodeI've NEVER seen a commercially produced outdoor forced air wood furnace.  Only wood boilers for hydronic heating or a heat exchanger in a standard furnace plenum.
Reply:Originally Posted by anickodeTheoretically, yes, unless you stick a blower on the combustion air inlet to get a rip-roaring blast furnace flame going in there, like he's planning to do...
Reply:Have you talked to your insurance company about this? You best! My insurance company has strict guidelines when installing one of these units on your rural property.There are many of those outdoor stoves in my rural area but they are hot water stoves with a circulating system on them. They burn wood and lots of it. They can also be used to heat your domestic hot water and save electricity.There are many different brands but the Central Boiler systems are one of the more popular units.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Going with 3/8 plate because it will mostly be burning coal. It will have a automatic damper on it. I am still debating on the blower in to the firebox don't think it needs it. The exhaust pipe will be about 6 inches into the box to keep the heat in longer I don't know about that partBut this is basically my plane Bear Cub 305-FA$2495.00Perfect for smaller homes, mobiles, modulars, shops, etc. this forced-air furnace is built tough and made to last just like our other wood furnaces.Door - 20" x 20" H.D. barrel hinged, double safety latch with handleFirebox - 3/8" ThickWood Area - 30" l x 30" hBTU - 140,000 approx.*Insulation - 1200 degree and the finest in the industry20" x 20" Wood Door w/ NO Ash Door or Grate SystemFramework - 14 gauge steelHot air chamber - 3/8" Thick Firebox surrounded by 16 gauge Air ChamberForced Air Front Door Damper System - activated by your thermostat in the house, it "fires up" your furnace when called for otherwise shutting air flow off saving you wood*Based on Maximum Capacity, Calculated w/ Dry Oak WoodMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:here is what i am talking about with the pipe Attached ImagesMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:I know a guy that did this with a Cramer woodstove. He buried the supply and return ducts. I think he put blue board  around them and coated them with tar to water proof them. Its his only source of heat so I guess it works pretty good. I think with your flue being that deep down in your fire box, you'll probably need a combustion blower.Safety 3rdGump
Reply:I was thinking the same thing with the blowerMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:definitely use water as a heat transfer medium. you really don't want to be blowing exhaust fumes into you house.all you'd need is some insulated PEX, a radiator and a fan.
Reply:Are you planning on lining the fire chamber with fire brick. I would think a red hot coal fire would reach forging temps on the bottom and sides of the fire chamber. I build a wood stove 30 years or so ago and used fire brick to line up to about 12 inches high. Helped to hold the heat and also kept the coals from melting the bottom of the fire chamber. I used it for about 3 years until the kids allergies visits to doctors cost more than I saved on burning wood.  I built it as a match to the Fisher Papa Bear stove, all 1/4 inch plate, stick welded then. Worked great just too much mold/smoke in house for allergies. I did use the ones called half brick they were about 1" thick  instead of 2.5" inches thick.
Reply:yes planning on having fire bricks on the insideMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:some progress Attached ImagesMiller 250 bobcat Miller super 32pEsab PCM 875Am curious as to what type of coal you plan on burning, anthracite or bituminous? And what are you planing on for the grates? Coal pretty much mandates cast iron and you'll need some kind of shaker setup to shake it down. As a side note-coal burns best in a Round fire box with straight walled sides.
Reply:The grate is going to be one inch rebar and for the coal I believe is Bituminous from Easter ky And the coal will be mainly to burn thru the night so the fire will still be there in the morningMiller 250 bobcat Miller super 32pEsab PCM 875
Reply:If the coal is from Eastern KY it is definitely bituminous. I have seen several home brew designs that used rebar for the grate- it will not last as long as cast iron, tends to warp and as I said you need to have a means to shake it down.  It appears from your comments you have never burned coal? it is not just 'toss some in' and it will keep the fire going until morning. Coal takes longer than wood to 'take off' and burn. You need more air UNDER the bed of coal than over top of it- about a 90/10 ratio with the 90 being from underneath. It also requires a chimney with a good draft, typically at least .06" on a manometer otherwise it will smother and not last thru the nite and to get it thru the nite you need to bank it properly. Not trying to insult you or your abilities, just trying to give you a heads up so you aren't disappointed. Biggest thing is make sure you have lots of air from under to feed the fire you may need to add an induction blower for the fire.
Reply:Originally Posted by beck549The grate is going to be one inch rebar and for the coal I believe is Bituminous from Easter ky And the coal will be mainly to burn thru the night so the fire will still be there in the morning
Reply:From coal country burned it all my life a large piece of coal will burn all nightI am not talking about burn small pieces of coal it will be 12x12 or bigger with wood in it to It won't be all coal about 75 wood 25 coal or whatever is in the yard at the time.Last edited by beck549; 07-28-2012 at 11:29 PM.Miller 250 bobcat Miller super 32pEsab PCM 875
Reply:I have a ''Fire Chief" outdoor wood furnace , forced air that is awesome , cool project!