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home made outdoor wood furnace... moved from wrong category Options
ajila ama farms
#1 Posted : Sunday, December 27, 2009 11:39:07 PM
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Posts: 134,494

Update on heater unit... It's still operating wonderfully, I couldn't be happier.  I did have an epiphany today though, I was thinking about my clothes dryer sucking air in from the house and spilling it back out again, at the moment I have the dyer exhaust run underneath the trailer (5-7ft of insulated underpinning).  I know moisture isn't good for under the house, but it's a cheap trailer and we'll be out of it in a couple more years of building on the house...

anyhow onto the new idea, I was thinking about how the dyer sucks air out of my house that has to be replaced with cold air seeping in from outside, this is a massive amount of air, and the dryer uses alot of electricity, since I now have a surplus of hot air coming from my new heater I thought of running a dedicated line from the heater to the air intake on the dryer, that way all i've got to run is the motor that turns the drum, installation of another damper to switch the dryer back and forth between regular use and wood heater use should be no problem, as well as a switch to turn off the dryer fan and heating element.  

I think this sounds like a real winner, just make the intake on your dryer so it sucks air from outside, under your home, or your attic during normal dryer operation with a damper to force air into it using your forced air wood furnace.  Think of all the power you would save as a dryer not only uses power itself, but also sucks cold air into your house thus lowering any home heater's efforts.   

I need to take my dryer in to my shop and pull it apart so I can make an intake for the air going into the dryer, It shouldn't be that hard to fashion some type of sheet metal box - to - 6 inch ducting so I can get started with this.   Seems like even without using the wood heater having your dyer suck air from someplace other than your living quarters would be a big help, and if the air is too cold going into your dryer then you could have the dryer exhaust be a 10 inch pipe with your six inch intake inside it, that way your dryer exhaust would pre-heat the air coming into it via conduction.  

Does anyone know of someone who has attempted such a system before?  any advice, comments, ideas on the subject?

davisonh
#2 Posted : Tuesday, December 29, 2009 2:05:46 AM
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Posts: 134,494

I know of a kit that is available whereas you take the gas burner or disconnect the electric elements of a clothes dryer and replace them with a hot water coil.Such a unit would be perfect for a wood boiler setup and I may be doing this this year so long as propane prices increase.Indeed I know the feeling ajila ;it is grand to be 'sticking it to the man'. I have owned my wood boiler for 6 years now and  would not be without it . I do not think I would be living here if I did not have it,my house would be foreclosed.One suggestion I have for your furnace is to automate the air intake system for combustion.You loads of wood'll last far longer when you dont need the heat.One washing machine (pull) solenoid,a spring and a hinged door iinstalled on the firebox door is all you need.Wire the solenoid to a disc thermostat or a remote bulb thermostat installed in your plenum to the house,or wire a relay to the solenoid and run the relay on a separate house thermostat.Wire the fan into that also,so the fan turns on when the solenoid opens the damper door.See the one reason I dont use more wood than I do is because when the water hits 190 degrees the damper shuts 'off' the fire,in other words the fire consumes all the oxygen in the firebox and it essentially becomes a vacuum in the firebox.Hot coals are still there,everything is still over 700-1000 degrees in there but there's no combustion.Man once that air hits it when the damper opens up it whooshes right back up again.

ajila ama farms
#3 Posted : Sunday, January 03, 2010 9:30:06 PM
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Posts: 134,494

very good idea davisonh, as I don't have a boiler it wouldn't quite suit me, but i'm sure someone checking out this thread will find a great use for it.  

as per your automated damper, that sounds nice, I need to do something to that effect, like I said earlier with my forced air furnace it gets too hot in the house and I have to send the heat under the house so I'm not sweating and miserable.  an automated damper would alleviate my problem of the fire staying hot all the time, but not completely smothering it.  

Update on the furnace 1-3-10...  I am having some welds pop loose on the exterior (air box), but it's no big deal as long as no welds on the firebox start coming loose.  I had thought about building one over the summer that is larger anyhow so that will definitely be  done now.  I don't think my small air leaks are worth dragging the welder to the stove or the stove to the welder so as long as they stay like they are it will be no big deal.   I kinda thought this one looked poorly made, but it still does it's purpose.  A person could spend 200-250 on steel (new price) and make a comparable stove to this one but much better if they were any good at welding.  

Wood usage...  I have been running this heater for about a month now, I have probably used 1 full cord of wood, but it has mostly been pine and poplar that has been laying around dead, so I am very happy with the wood usage.  I do have a face cord of unseasoned split oak that I use just before I go to bed at night, but it is lasting a very long time, there is hardly a dent in it.  I burn my trash wood all day and most of the evening, try to get a good bed of coals, then jam it full of the unseasoned oak.  The oak isn't completely green but it is far from dry.  Seems to be working out great for me.  Now I am in the "south" so it doesn't get as cold here as it would in say, minnesota, but last night it got down to 10 degrees (F) and it was 84 inside my house, so that's pretty good.  I would think this exact same unit in a very well insulated house would easily heat 2,000-2,500 sq. ft.  and be very comfortable.  As mentioned before this trailer I am in now is roughly 1,000 sq. ft. (a little less) but is an old trailer with very little insulation.

Anyone thinking of doing an outdoor system should do it!!!!  A forced air system is very simple and very easy to make yourself with a small amount of tools and knowhow.  The boiler type as they are better heaters seem alot harder to safely make yourself and cost alot if bought new, but if you have the skills or the money to buy one go for it, you won't be dissapointed.  Sure you have to go outside to feed it, but you have to go outside to get wood for your wood stove anyhow, plus even at 10 degrees it's very refreshing and a nice break to go outside to feed it.  We both smoke, but don't smoke in the house, so I go outside periodically anyhow.   All in all it is a win-win.  The best part is I just got my power bill, I am using less than half of the electricity that I did last year at this time, and my power bill was only $118!!!!  That is including heating!!!   Last year it was nearly $400!!!  

sorry if I seem a little long winded but I really want to see more of these systems in the south, they are pretty common in the north, but I get alot of my neighbors coming around asking me what the big smoking box is...  I wish they would all install them ( of course then I wouldn't be able to cut their dead pines for my fire).  

do yourself a favor and get one of these systems going!!!

ajila ama farms
#4 Posted : Sunday, January 03, 2010 9:30:06 PM
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Posts: 134,494

Ok, so here goes, this will be a rather long post I believe...


First off let me start by saying this is my first post to mother earth news, I'm sure there are other articles that involve outdoor wood furnaces, but after much searching before building mine, I feel that I need to add a bit of truth to the whole area from someone who built one himself.  A heater of this type would not be very economical if you were having to buy your wood, so if you are lazy, live in the suburbs, or just don't have a way to get the wood yourself, stay with something commercial like oil, gas, or electric heating.  For those of us "modern homesteaders" this is a great way to heat your house for virtually nothing.


Why Am I doing this?  well for one, our electric furnace made our heating bills hit 400 dollars and up last winter, that will not be happening again.  Also I have lots of standing beetle killed pine on my property so with an outdoor unit the whole flue fire issue is completely nill.  With these units you can burn things that you would not want to burn in a heater inside your house, burning pine will make too much creosote build up in your chimney and can be very dangerous (I have survived 2 chimney fires when I was young), plus you can really burn anything.  If a person so chose to they could burn tires, shingles, whatever but without a catalytic converter stove that would be a big no no for the environment.  The only electricity that I am using is a small fan that uses 240 watts on it's highest setting, of course you could easily use some type of 12 volt fan and run the system off of batteries charged by a bank of solar collectors and have central heating with zero utility bills.  So in actual money out of pocket for bills I'm heating my house with roughly 2 lightbulbs.  That's pretty cool!!!  I hope this writeup will help someone like me who was just swamped by too much info (most of it bad) and getting the head spins by the high prices of buying one of these things.  If I had the money to spend I would love to have bought a nice ready made unit, but hey I spent 10% of what the cheapest unit cost, and I couldn't imagine it making my house any warmer...


I encountered so many "experts" on the subject telling me this and that and how I needed to do it and blah blah blah that i got completely fed up and went with my own design and trashed every bit of info that I was told.  I grew up with wood heat so that coupled with the fact that I am a home mechanic and have a degree in radiation physics should qualify me to be an "expert"... (sorry, that last bit was for all the nay sayers that will inevitably come along to say that I don't know what i'm doing)...  I was told that heating air is terribly inefficient, and basically that I was a fool for not making a boiler type heater...  Well, those sounded like way too much trouble and expense for the net gain over what I wanted to build, so I ignored all the "advice" that I had gotten and just did this whole thing myself...


All you have to have to get started with this project is a double walled wood stove, I found one on internet classifieds for $200 bucks, it was a rusty hulk out in a junked up yard but it works just fine.  You can easily make one if you have a welder and some metal, but I would suggest looking in the classifieds first.  This one has an ash drawer which is pretty nice but is not at all necessary.  For simplicity sake, lets call the "firebox" where the fire is, and the "airbox" where your air circulates for heating.  The key is you want the firebox to be totally sealed off from an outer metal box, the front and rear of my heater are single walled and the flue exits the back.  The bottom, top and sides are all double walled with about 2 inches between the inner and outer walls.  There is a hole in the bottom (for forced air intake) and a hole at the top (for forced air exhaust).  What you want to happen is to circulate the air around a fire box, with absolutely no way of smoke getting in your heating air.  If I had built this myself, or if I decide to make another one I will add heat sinks along the outside of the firebox, but inside of the airbox. Just to maximize heat transfer (although it isn't really needed).  


So we've covered the actual wood heater, any kind would work as long as you can have 2 chambers, one for fire, wood, smoke; and the other for "clean" heated air.  Of course the more efficient heater you have the better off you would be.  One word of advice is to get the largest heater you can find, larger firebox = less trips outside to fill it.  


Next I made a small building to put the stove in, this is not completely necessary but I did not want to waste my heat by heating nature.  The whole building started with a skid.  I love making buildings on skids, that way you can move them where they are needed.  The other reason for a skid mount is just in case something went wrong, I can hitch up to it via a cable and jerk it away from the house...  The skid size will depend on your stove size, mine is rather small so a 4' x 4' was perfect to give me about 8 inches on any side of the stove, and about 5' tall.  I made the skid rails with 8" x 8" pressure treated beams.  All the walls and interior ceiling were covered in 1/2" tile backer board (durock).  I did not want any exposed wood inside the heater building.  After you're done you should have a completely fireproof surface inside the building.  Of course you could just as easily buy one of the cheap $300 dollar metal lawn mower sheds from lowe's.  For siding I will be using roofing metal because I want this building to be made from as little combustible material as possible.  The siding is not on the building yet as I have wanted to experiment with it in all possible situations before I cover the 2x4 studs.   On the exit hole of my flue pipe I put several layers of metal flashing in concentric circles around the pipe so that there is not a direct line for the heat to get to the studs on the back wall, if yours exits the ceiling try and do the same to protect the rafters.  


The whole front wall of my building is removable with 4 screws, but there is a 2'x2' door that gives me access for adding wood and using the ash drawer.  The door is also covered in backer board.  Again I wanted no exposed combustible material at all.  


Now for the air circulation system.  On the exit of your heater the air will be very hot, I used metal duct work wrapped in fiberglass insulation so it would not melt, After about 5 feet of that I went to regular insulated ducting (plastic and fiberglass wrapped in shiny mylar).  You will want to push the air through your "airbox" not pull it.  If you pull it it will overheat your fan (unless you have a nice high heat fan).  You also want a "closed loop" for the air in your house, meaning the air you are pushing into the airbox is supplied via an air return from the house.  Basically all you have to do is cut a hole someplace where you would like it to be, and run your ducting from there to your fan.  Here is a line of how it should go  cold air return--->  duct work --->fan----> more ductwork --->airbox of heater ---> ductwork----> house...  I already had central heating so I hooked up the duct work to the existing vents that go all through my house.  You will want a damper between the heater and your house so if you use your central unit it won't waste by blowing into the unused wood heater.  This can be easily done by a piece of flashing attached only by the top so it will lay down when your wood heater is not in use and block off the ducting, but when you start your wood heat fan it will blow it open.  The closed loop is essential here, you don't want to heat cold outside air and then blow that in your house, and you definitely don't want to be sucking air from your heater building as that will suck smoke out of your firebox and blow it in your house.  Something else that is nice is my heater has thermostats mounted on the body of the heater, when they get hot they complete the circuit and allow the fan to turn on, when the fire goes out, the fan turns off so you aren't blowing cold air into your house (like early in the morning if the fire goes out).  It took a minimal amount of wiring to get this to work properly, and is a highly reccomended part of the system.  


That's it...  so lets do a quick recap, there is a double walled heater inside a  box to insulate it from the cold outside air.  I then have a closed loop of duct work to keep the air circulating in my house.  voila, you have nearly free heat.  It cost me about $500 bucks total to build everything, and that is buying the wood stove, if you can make one with scrap metal that's great, just make sure it's heavy enough to withstand the fire, you don't want a hole burning in it and blowing fire into your house.   Now how does it work...  well, I am living in a 1,000 sq ft. mobile home while building our house, as I type it is 88 degrees inside the house, and 30 outside.  The mobile home is an old one (1980's) with the old 2x3 walls ( not 2x4) and very little insulation.  We have the front door open right now to let out the excess heat.  The only modification I'll be making is a manual damper so when it gets really hot like it is now, I can blow the heat under the house rather than totally wasting it.  I have roughly a 13" high, 20" deep and 13" wide firebox, after I get a good coal bed I only have to load it 3-5 times a day and find myself putting lots of green wood in it so slow it down some.  Before bed I load it up with unseasoned wood and still have plenty of coals left even if I sleep in in the morning.  This thing is great, I love it and will never have a house without one.  


What else can be done with it?  well since we own a farm we grow lots of herbs, so in the summer it should be very nice to have a source of smoke free heat to dry veggies and herbs with.  It would also be very easy to heat water with the system, just run some pipes through it, although I would not reccomend doing this in the winter, you have a greater chance of freezing pipes then.  A larger unit could easily heat a much bigger house and an outbuilding or two.  Just remember you want to be heating air that is already warm (like what's in your house as opposed to outside air), and use insulated ducting to pipe the heat wherever you want it to be.  This heater should pay for itself in 2 months, and since I didn't remove my existing electric furnace I've still got the thermostat on the wall that I can turn up if i'm feeling too poorly to mess with a fire.  


I'd be more than happy to help anyone with the building of their unit, and would much rather see people using these and "giving the finger" to utility companies.  Our local utility company was indicted for price gouging last winter (yahooooo) so nothing pleases me more than to pay them less 

Of course something else that needs mentioned is that any wood heat is dangerous, smoke detectors and good fire extinguishers are a sound investment, however this unit should be much much safer than an in house wood heater.  I guess the safest would be a non-pressurized boiler, but as I mentioned earlier I did not feel that the net gain would be worth it to build or buy one of those.

conact ajila ama farms at....   blackbirdphotography2@gmail.com

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