# How to build a outdoor wood boiler



## cowboyup05

Any one have any plans on building a outdoor wood boiler? Any help would be great.


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## ericjeeper

you need to build a water heater that is not pressurized. Do a search on the net.. The trick is to make it efficient.. That is the hard part.. Anyone can weld up a firebox within a large tank of water.


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## MN Mom

Another idea is what are you going to do when the electicity goes out? unless you have a battery backup 12v. pump you are going to get cold.


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## MN Mom

Layed in bed this morning and thought about this (raining outside).

55 gal barrel on its side. Pipes running through the top of the barrel in a loop pattern. insulate the outside of the barrel. pump water through the pipe system.

problems though are you only get a 10" x 10" door and the build up on the pipes might be a problem.

If you are going to use a boiler system you might want to put in a infloor heat cement floor. Have heard they stay warm fo up to 3 days with the heat shut off.

Just a thought.


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## Ross

There have been several articles in Farm Show magazine about people building thier own. They have a website but I've never found it easy to search. http://www.farmshow.com/


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## agmantoo

I have been disappointed with the design where the stove fits in the storage tank. IF I ever have another outdoor wood fired boiler it will be two components. A firebox and a storage tank and they will be separate. I have spent time studing the various designs on the market and the ones I have seen are too short lived for the investment. The best idea that I have come across is to duplicate the method that is used to heat scalding tanks in slaughter houses. The slaughter house units are fired with natural or propane but a wood fired heater should be feasible. The technique is to heat a series of pipes and using the temperature differential to create a thermosyphon flow of hot water to the non pressured storage tank. This setup circulates the hottest water from the heater to the tank and from the tank the cooler water returns. A coil of copper tubing could be submersed in the storage tank for potable hot water. A design of this type would permit the storage tank and domestic water heater to last and the wood fired heater could be serviced or replaced as needed. The storage tank could be remotely located if desired by using a small fractional horsepower pump to circulate the water between the tank and the heater.


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## PyroDon

agmantoo
The idea is sound though you wont be able to thermosyphon on a remore tank.
Putting the tank in the basement with an outside vent would make it work a bit better . You will still need the circulation pump .
for the fire box I would suggest stainless pipe inbedded in sand and make the fire box as large as possible . as to allow large chunks of wood (less splitting longer burn time) . Once the sand is up to temp it wont take much to keep it there. such a system can easily be augmented with solar as well.


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## agmantoo

PyroDon, thanks for the sand suggestion! That is a great idea. My house is on a small hill and I think that if I were to elevate the storage tank in the basement I could achieve the thermosyphon. I have a level walkout basement door and I could put the heater farther downhill. With my previous boiler I would heat the water by burning the stove real hot until the water reached around 190 degrees F then I would let the fire die until the next firing. In so doing, don't you think the temperature would achieve enough temperature difference to create the flow? I live in a fairly mild climate (zone 7) and firing the stove in this manner seemed more efficient and the burn was a lot cleaner (less smoke). The old system had a large storage capacity so the heated stored water would last a minimum of 12 hours. I am currently heating with a geothermal heatpump that uses well water. The price of electricity will mandate the direction I take.


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## PyroDon

My main problem with the thermosyphon is pssible vapor bubbles in the coils. 
you could still have the force air in the fire chamber .
Im working on a design myself with a limited budget '.
I'd like to get a few cast iron radiators to use in the fire chamber for heating the water . Stainless is beyond my budget at the moment. 
I'll have to have something before winter hits even if its just a fireplace insert .
I have a nice one of those built already and have used it as a stnd alone stove in the work shop.


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## dennisjp

Dont have any plans drawn, but am thinking about the same thing Cowboy.
I have an idea that could be tossed around here.
A BTU is the amount of energy that it takes to raise or lower a pound (LB.) of water one degree. A gallon of fresh water weighes 8.34 lbs.
If one were to bury an old 20,000 gal. fuel tank, that "CAN BE FOUND FOR HAULING COST" and hooked it to a solar panel so that the water was heated during the summer to a temp of 200 degrees or so, there would be a lot of stored heat in that tank. The right solar panels heat water to a point of creating steam, so 200 deg. is reasonable.
OK, a 20,000 gal. tank x 8.34 x 70 degrees of useable heat would be nearly 12 million BTU's of nearly free heat. It could thermosyphon during the summer and you wouldn't need a pump until you needed the heat. 
I don't understand why someone doesn't do this. A simple to make solar panel would do the heating, and they are digging up old gas tanks every time they move a gas station. They have to pay to get rid of them and all it would take is a tank full of water and a cart full of GAIN washing powder to clean them enough to use.
The sun would even be heating the water during the fall and even the winter on sunny days. It would be atleast a couple of months before you ever needed to fire up the boiler, and even then, the sun would be helping on the sunny days. 
Any ideas out there????????
It just seems like a good idea to me.
Well, it was just an idea. One that I intend on proving, as soon as I can aford to, lol.


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## rambler

Interesting.

What do you do about heat loss? Earth temp is about 55 degrees, with the tank in the ground, on the surface area of a 20,000 tank, and you collect heat 1/3 of the time in summer, you lose heat to earth 3/3 of the time, you might have a hard time gaining any btu's at all in the water?

--->Paul


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## dennisjp

rambler said:


> Interesting.
> 
> What do you do about heat loss? Earth temp is about 55 degrees, with the tank in the ground, on the surface area of a 20,000 tank, and you collect heat 1/3 of the time in summer, you lose heat to earth 3/3 of the time, you might have a hard time gaining any btu's at all in the water?
> 
> --->Paul


I'm sure you would loose a lot of heat at the begining but it seems to me that long before the summer was out, the ground would warm up so the losses wouldn't be all that bad. Earth is also an insulator. Like a brick wall in dirrect sunlight heats up and store the heat for a period of time. Just thinking. LOL


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## michiganfarmer

Ive built 2 of them. One for me, and one for my dad. Here are some pictures. If you have any questions feel free to call me at my business. 1-866-941-8003.





The burn chamber is a 500 gallon propane tank I bought used from Ferrel gas. It cost $50. The water jacket is 1/4" plate I welded together. I hade the bottom half rolled, and I used plate for the rest of the sides and top. The whole thing with pumps, tubing, and the coil that goes in my existing forced air furnace cost about $3000.


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## ericjeeper

The sun will only heat so many gallons of water a day. I have six panels. they are 3x16 feet/ They will just make 500 gallons of hot water a day here in Indiana..so basically 20,000 gallons is wayout of reach. That would be like trying to heat a swimming pool with a candle.


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## rambler

dennisjp said:


> I'm sure you would loose a lot of heat at the begining but it seems to me that long before the summer was out, the ground would warm up so the losses wouldn't be all that bad. Earth is also an insulator. Like a brick wall in dirrect sunlight heats up and store the heat for a period of time. Just thinking. LOL


I think you are vastly underestamating the heat loss. The earth will radiate the heat away to the 55 degree soil around it. You may wish to look into earth tube heat pumps (ait tubes below the frost line to heat a house over winter, drawing heat from the 55 degree earth).

As well, you would need a massively huge solar array to collect enough heat to collect those kinds of BTUs. Might wish to look into the solar radiation available in your area, & the efficiencies of collecting it.

Not trying to end your project: just want you to see the realities of it before buying materials. 

--->Paul


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## CatsPaw

Had this discussion with a friend about a week ago. I second the propane tank as a boiler.

I would re-think the sand. I haven't resolved this myself, but, here's what I understand.

Sand is basically glass, an insulator. What do you want to do? Insulate the box, or do you want a thermal mass to store heat. Sand won't work as a thermal mass. Then again, as an insulator, wouldn't "all" the heat go into a coil wrapped around a boiler insulated by sand?

I'm not stating an answer, I'm trying to understand what would be better in regards to an outdoor furnace.


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## Ross

An insulator needs to trap air, compacted sand has little trapped air so the silica should be a good thermal mass should it not? Never heard glass called an insulator (except in electricity) it has absolutly no trapped air space, and conducts heat very well. Or at least our glass cooking pots do.


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## rambler

Glass is a wonderful electrical insulator, but a very, very poor thermal insulator.

Sand stores a load of heat - if you insulate it.

--->Paul


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## Ed K

ericjeeper said:


> The trick is to make it efficient.. That is the hard part.. Anyone can weld up a firebox within a large tank of water.


I agree with this comment. When I was young we heated our garage with a 2 55 gallon drum woodburner kit. Worked great.

We decided to make a woodburning stove. We built a big one and even lined it with firebrick like a commercial woodburner we had in the house. You could feed a log into it bigger than you could easily lift but it didn't put as much heat in the building in the garage as the two barrel stove kit did.

If you plan to do it I hope you find some proven plans.


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## MELOC

just wondering...wouldn't any thermal bank like heated sand, etc. that is buried lose heat if the ground becomes wet?


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## CatsPaw

I think that the fact that (as a window would) glass would transfer heat from the boiler to whatever is around it, like, outside. Water is also and excellent thermal conductor. Just as cold water will put you into thermal shock very quickly.

I was reading up on bread ovens. The document from an apparent authority said specifically not to use sand. I think the nail was hit squarely here. I think sand (glass) is a thermal conductor, not insulator. That would explain why deserts can be freezing at night. None of that sand is retaining the heat.

I'm thinking rocks are good. Meaning limestome [dust], granite, sandstone, something without the silica or quartz. Clay makes a good wood fired oven.

How about this. A propane tank with the end cut off. Fire door welded to it, nice and big for loading. Wrap coils of copper (IF you can afford it now) or other heat proof tubing. Coat with refractory mortar to stabilized the tubing around the tank. Encase with a TBD thermal mass...(TBD = corporate lingo for To Be Determined.)

I might be concerned about thermal expansion effects on mortaring the tubing to the tank, though. Yeah, bad idea.


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## dennisjp

cowboyup05 said:


> Any one have any plans on building a outdoor wood boiler? Any help would be great.


Looks to me like you should call michiganfarmer. Looks like he has got it going on. 

michigan, do you install this in any type of a shed or encloser, like the ones in ads you see, and what do you insulate it with??
Looks like a fine job from the pictures. Also, how long will a load of wood burn on say a 30 degree day. Do you have any type of draft controller on it?

Another question, is couldn't you get different sizes of tanks at that price so that one would fit into another one instead of having to pay the $$$$$$$$$$ for the 1/4" plate metal. I know that ate a hole in the pocket. I just bought some tubing and a little plate and it was well over a hundred dollars. 
And what kind of pump did you use and where did you get the pump from ? locally or did you order it?
Again, It looks like a dang nice job. You should think about selling plans for it. That would be easy money, if there is such a monster. LOL.


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## michiganfarmer

dennisjp said:


> Looks to me like you should call michiganfarmer. Looks like he has got it going on.
> 
> michigan, do you install this in any type of a shed or encloser, like the ones in ads you see, and what do you insulate it with??
> Looks like a fine job from the pictures. Also, how long will a load of wood burn on say a 30 degree day. Do you have any type of draft controller on it?
> 
> Another question, is couldn't you get different sizes of tanks at that price so that one would fit into another one instead of having to pay the $$$$$$$$$$ for the 1/4" plate metal. I know that ate a hole in the pocket. I just bought some tubing and a little plate and it was well over a hundred dollars.
> And what kind of pump did you use and where did you get the pump from ? locally or did you order it?
> Again, It looks like a dang nice job. You should think about selling plans for it. That would be easy money, if there is such a monster. LOL.


I poured a concrete slab 10' by 10', set the furnace on it, and built a shed arount it. I insulated the ceiling with some blown insulation I got for free. I didint insulate the sides, but my dad got ahold of a bunch of batt insulation for free, and he is going to dive me some so I will insulate the walls before this winter.

The burn chamber is 40 inches in diameter. If I fill it with 2' logs it will hold a fire 24 hours in 20 degree weather. In 30-50 degree weather it will hold a fire 2 days, and the hot water will continue heating the house for another day. It holds about 280 gallons.

I cut a 4" square hole in the back of the burn chamber, and welded a 1' piece of 4" square pipe in it, cut and bent, and rewelded the pipe so it points straight up after it comes out of the back. I welded a small bracket on the top of the pipe, mounted a 115 volt solonoid to it. I laid a piece of 1/8" plate on top of the pipe, and attached it to the solonoid. I installed a thermostat(aquastat) in the waterjacket. I wired the thermostat to the solonoid. When the water temp gets down to 150 the thermostat send power to the solonoid witch pulls the plate off the pipe to let the fire breath. When the water gets to 190 the thermostat shuts the solonoid off. 

The water jacket cost me about $800. I thought about buying 2 different size propane tanks, but the 500 gallon tank I bought was the biggest there was except for the huge 10' diameter bulk tanks. I couldnt find the size I wanted for a water jacket so I built it. I bought the pump from the local outdoor wood furnace dealer. Its a grundfost, or something like that. It cost about $75.


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## dennisjp

Don't tell michiganfarmer you can't do something. You got it going on, sir. 
I like the draft control you have and will be getting back to you because I think I will build a smaller unit to put in the basement. I am an electrician, but the selonoid thing is beyond by abilities of figureing out what I would need by myself. Thanks for the ideas. 
I already have a water tank that is 28" in dia. and about 60" tall. My sister has an old water heater in her basement that I think will give enough room for a water jacket around it. It will just hold a small fire but I am just getting over a fall I took a couple of years ago and will be down in the basement working alot this winter, so I can keep it stoked pretty good. 
I am think of using a car heater coil in the livung room and my daughters bedroom with a small electric fan all built in a metal box. Any ideas how big a pump I would need???????
Another question. The large tank is galvanized. I have been sick from welding the stuff before, and trust me, I know to keep my nose out of the fumes when welding it as best you can and I know to drink a lot of milk while doing so, but I was wondering what you thought. Will the water jacket get hot enough to put off fumes when you light a fire in the burner????????? 
It is an old tank and the gal. is thick. I don't think I could grind it off in a year and you know how the [email protected]#$ sticks to grinding wheels. 
Thanks again for the pictures and info. 
Dennis


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## michiganfarmer

dennisjp said:


> Don't tell michiganfarmer you can't do something. You got it going on, sir.
> I like the draft control you have and will be getting back to you because I think I will build a smaller unit to put in the basement. I am an electrician, but the selonoid thing is beyond by abilities of figureing out what I would need by myself. Thanks for the ideas.
> I already have a water tank that is 28" in dia. and about 60" tall. My sister has an old water heater in her basement that I think will give enough room for a water jacket around it. It will just hold a small fire but I am just getting over a fall I took a couple of years ago and will be down in the basement working alot this winter, so I can keep it stoked pretty good.
> I am think of using a car heater coil in the livung room and my daughters bedroom with a small electric fan all built in a metal box. Any ideas how big a pump I would need???????
> Another question. The large tank is galvanized. I have been sick from welding the stuff before, and trust me, I know to keep my nose out of the fumes when welding it as best you can and I know to drink a lot of milk while doing so, but I was wondering what you thought. Will the water jacket get hot enough to put off fumes when you light a fire in the burner?????????
> It is an old tank and the gal. is thick. I don't think I could grind it off in a year and you know how the [email protected]#$ sticks to grinding wheels.
> Thanks again for the pictures and info.
> Dennis


Id like to have mine in the basement so whatever heat bleeds off the furnace will stay in the house, but the reason I built it was to get away from putting wood in the basement.
This is the pump I use.
http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?
ItemId=1611762357

When Im welding galvanised, I put a fan near my head, and turn it on. Ive never gotten sick, but everyone is different too.

The water jacket only gets up to 212 degrees. Im sure galvanise wont burn off at 212.


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## tiogacounty

CatsPaw said:


> Had this discussion with a friend about a week ago. I second the propane tank as a boiler.
> 
> I would re-think the sand. I haven't resolved this myself, but, here's what I understand.
> 
> Sand is basically glass, an insulator. What do you want to do? Insulate the box, or do you want a thermal mass to store heat. Sand won't work as a thermal mass. Then again, as an insulator, wouldn't "all" the heat go into a coil wrapped around a boiler insulated by sand?
> 
> I'm not stating an answer, I'm trying to understand what would be better in regards to an outdoor furnace.


 Actually, sand is an excellent storage media for this application. Decades ago there was an alternative heating sytem that involved building a small shed out of block and using it as the outside shell of the boiler. IIRC the building was roughly 8' square and 8' tall. It had aluminum siding and a gable roof with shingles. It looked like a giant dog house. The boiler heated a network of pipes that were buried in tons of sand. The sand retained enormous amounts of heat and the boiler could maintain heat with quick small fires. My buddies parents had one on their farm when I was a kid. The only things I recall is that is was called a "Hasha" or something similar and it was advertized in the Mother Earth News.


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