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 Outdoor Wood Boiler

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greenenergyexperimenter



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PostSubject: Outdoor Wood Boiler   Fri Oct 10, 2014 4:16 am

Here's a new build that I recently completed and plan to use to heat my home with this winter:



It is not a rocket stove, but does incorporate a heavily insulated burn chamber. I do plan to add a secondary air system in the near future, but it does produce pretty clean exhaust as is:



The most expensive part of this build is not the stove itself - it is hooking it up to hydronics! I'll be putting up a video on how I did that in the near future. I also plan to use the heat from the stove body (under the boiling point of water over most of it) to preheat combustion air to further increase efficiency.
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Sat Oct 11, 2014 12:58 pm

Here's the video on how the heat is brought indoors:



As you can tell, it is simple, yet effective.
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caotropheus
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PostSubject: Re: Outdoor Wood Boiler   Sat Oct 11, 2014 2:11 pm

Nice boiler. I like the idea of using expansion gaps to avoid insulation to crack. I know nothing about wood boilers, all the remarks I will make are based on my wood stove experiences. Secondary air may hopefully help you to get the boiler a bit hotter, so here comes the first question, is it possible to make a baffle of some sort between the water container and the chimney exit to keep the heat a bit longer inside the stove? I think that if hot secondary air is inserted into the stove just underneath the baffle, it will allow you to save fuel and increase temperatures. I think that using your current configuration, some heat will escape up the chimney. Probably you may even recuperate some of this heat...
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Sun Oct 12, 2014 1:22 am

caotropheus wrote:
Nice boiler. I like the idea of using expansion gaps to avoid insulation to crack. I know nothing about wood boilers, all the remarks I will make are based on my wood stove experiences. Secondary air may hopefully help you to get the boiler a bit hotter, so here comes the first question, is it possible to make a baffle of some sort between the water container and the chimney exit to keep the heat a bit longer inside the stove? I think that if hot secondary air is inserted into the stove just underneath the baffle, it will allow you to save fuel and increase temperatures. I think that using your current configuration, some heat will escape up the chimney. Probably you may even recuperate some of this heat...

Thanks! I am working on installing a baffle, as more heat is escaping than I like. I've also been experimenting with secondary air injection, similar to what I did with my cinderblock stove. I also plan to make a heat reclaimer to preheat combustion air with the heat that comes off the body of the stove.

Here's some temperature data that I've gathered so far. After running the stove all day, the hottest measured point on the body of the stove is 250 *F, with the average top temperature being 190 and the bottom 120. The hottest measured internal temperature was 1246 *F and rising (my thermocouple is only good to 1400). The hottest exhaust is 343 *F.

I'm hoping to get the exhaust down to 275 *F.

BTU and efficiency calculations are still a work in progress, since it hasn't been too cold.
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JeffJetisoned



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PostSubject: Re: Outdoor Wood Boiler   Mon Oct 13, 2014 2:01 pm

Good one. I would like to hear more from ya and see the whole set up in diagram form if nothing else. I've thought about building something like this stove placing the water tank inside the flue pipe instead of in the fire chamber, vortexing and using secondary air to entrance of flue pipe. Your positioning of tank might be better...don't know...but think it harder to take advantage of rocket stove technology and secondary air. Thanks for posting and this definately give me something to think about.
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Hitchhiker



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PostSubject: Re: Outdoor Wood Boiler   Tue Oct 14, 2014 5:09 pm

That is cool, green.
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Tue Oct 14, 2014 5:19 pm

JeffJetisoned wrote:
Good one.  I would like to hear more from ya and see the whole set up in diagram form if nothing else.  I've thought about building something like this stove placing the water tank inside the flue pipe instead of in the fire chamber, vortexing and using secondary air to entrance of flue pipe.  Your positioning of tank might be better...don't know...but think it harder to take advantage of rocket stove technology and secondary air.  Thanks for posting and this definately give me something to think about.

Thanks, guys!

I'll try to get some more details on it soon for you. I, too, was concerned about what putting the tank inside the fire chamber would do. It does soot the tank a bit. Right behind the tank, there is a small dark circle on the insulation. The rest of the insulation is soot free.

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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Thu Oct 16, 2014 5:02 am

Ok, I apologize for the childlike drawing, but here is a cross section of my boiler for you, JeffJetisoned:



This shows the new baffle system that I'm experimenting with. Yesterday, I put in the baffle on the top left and have observed a average 22 *F drop in exhaust temperature. This morning, I installed the bottom baffle, but it is too hot to run the stove today, so testing will have to continue at a later time.

The area between the grate and the lower baffle is where I plan to put in a secondary air injection system. The air will preheat from the coals on the grate.
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gadily
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PostSubject: Re: Outdoor Wood Boiler   Thu Oct 16, 2014 10:08 am

also with exhaust been too high if you vortex it and run a preheat pipe before the main heat of the boiler you wouldnt be taking much heat out and you would warm the water much quicker from the excess heat in the exhaust pipe therefore cooling the exhaust system

its why they use pre heating in different stages before the main heat of the boiler is used
a 2 stage heating system is better than one and a 3 stage heating system is better still also works if creating a steam system
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caotropheus
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PostSubject: Re: Outdoor Wood Boiler   Thu Oct 16, 2014 2:04 pm

Green,

Looking forward to see a video of the new improvements you made, including the secondary air...
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Thebigflyin

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PostSubject: Re: Outdoor Wood Boiler   Fri Oct 17, 2014 12:33 am

looking good
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Fri Oct 17, 2014 4:47 am

gadily wrote:
also with exhaust been too high if you vortex it and run a preheat pipe before the main heat of the boiler you wouldnt be taking much heat out and you would warm the water much quicker from the excess heat in the exhaust pipe therefore cooling the exhaust system

its why they use pre heating in different stages before the main heat of the boiler is used
a 2 stage heating system is better than one and a 3 stage heating system is better still also works if creating a steam system

Great idea! I have 60' of 3/8" coiled copper pipe from my old rocket stove boiler that I could place in the flue pipe to preheat the water.

It looks like I've got a couple days of nice weather ahead of me to make the modifications cheers

caotropheus - I'll be sure to get video footage of the improvements I make
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JeffJetisoned



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PostSubject: Re: Outdoor Wood Boiler   Mon Oct 20, 2014 1:23 am

After giving this project some thought, I don't know if having a tank inside the fire chamber or flue pipe would be better than the copper coil inside the flue and holding tank inside the house. The cool down times in between burns might be less efficient than the temp difference by have it in a heated house, not to mention the mass heat that escapes the tank and if hooked up properly, could have a fan behind it or a section of it for humidity control. I've seen these humidifiers that have a float sytem and heating element in them with a temp controlled fan. It obviously takes longer to boil cold water than warm water. What happens when water freezes from not having the fire going, unless your using anti-freesze and heating condenser, and then that eliminates the hot water heater. It may or may not be a problem, depending on where you live and how often you are able to feed the fire. At any rate, I like the project because it is made from re-claimed materals and like I always say, nothing wrong with free. Hot water heaters are one of the most expensive appliances in a house to run. Thanks again for posting and look forward to everyone's ideas and input.
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Mon Oct 20, 2014 3:12 am

Thank you, it is hard to beat nearly free! I use antifreeze, I tried a system without and paid dearly for it with burst pipes.

Storing the excess heat would have many benefits and that is something that could be done with a discarded hot water tank in good condition. Having a temperature controlled bypass valve would allow you to choose heating the house first, then heating the storage water.

I think having coils in the flue plus a tank in the box would be the ideal setup. I've built systems with coils in the flue and now the one with a small tank in the firebox. The advantage of the coils in the flue is it really cools the exhaust. Once there is no active fire, the advantage disappears. They fail to extract heat from the coals.

The boiler tank lets a lot of heat go up the flue when the fire is really active. The rest of the time, it does a great job of extracting heat.

Combining the two like gadily suggested would give you the best of both worlds.
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gadily
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PostSubject: Re: Outdoor Wood Boiler   Tue Oct 21, 2014 10:19 am

it does more than that it gives higher btu,s of heat flowing to your heating system

http://homerepair.about.com/od/heatingcoolingrepair/ss/Anatomy-Of-A-High-Efficiency-Condensing-Furnace_5.htm

this is a 3 pass system can be incorporated into wood burners in the same way

http://www.madehow.com/Volume-7/Furnace.html

remember each pass makes higher btu output of your system in the above its 25,000btu primary
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Fri Oct 31, 2014 12:53 pm

Gadily, you have created a beast cheers

I added 40' of 3/8" OD copper tubing to the black stovepipe. This preheats the water going into the boiler tank as you suggested. The water is fed top down. Here's how it looks:



Two stages are almost too effective. I built the fire with too much kindling, resulting in a boil over. Fortunately, the vent system works well, preventing any damage. Feeding it with big hunks of wood prevents boiling.

I've also added a damper that reduces the amount of air going in. It is not air tight, and it still burns clear and odorless.

The stovepipe temperature right after the coils now is always under 250*F. I really can't ask for more than insulating everything.

I'll put up a video soon on the modifications I've made. Thanks again for all the suggestions, it has made a huge difference!
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gadily
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PostSubject: Re: Outdoor Wood Boiler   Sat Nov 01, 2014 6:58 am

if you want to improve it even more use a mono block/back boiler at top of chimney before a final exit to outside this will reduce the temperature even more on exit gasses

if you decide to add another stage you need something like this

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gadily
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PostSubject: Re: Outdoor Wood Boiler   Mon Nov 17, 2014 11:28 am

i found your vid lol



with your chimney condensating what I believe is happening is that your water in the return is too cold on a closed loop system or gravity fed system it will disapear if not you must allow some heat to return back through the preheating coil

this way can also damage your piping and cause the system to rust out by condensating at the boiler



though ive got to ask is how much wood does it use by a cord of wood per day
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greenenergyexperimenter



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PostSubject: Re: Outdoor Wood Boiler   Tue Nov 18, 2014 6:40 am

I've got the condensating problem fixed with a digital temperature controller. Talk about better than a snap switch!



We've had a really cold snap, with overnight lows in the single digits (*F) and daytime highs in the 20's. At these temperatures, I'll go through a cord of green wood in 22 days. I'm unfortunately having to burn green wood. If the flame hits the copper coils, I get flash steam and everything grinds to a halt.

This forces me to choose between constantly tending a small fire of seasoned wood, or going with a longer burn with green wood. With these temperatures, I'm going with the green wood. The good news is it burns smokeless even with the green wood.

I'm building a new exchanger that should avoid the flash steam problem and will install it as soon as the cold breaks. I'm also building a forced air induction system that will give me even better temperature control.
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gadily
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PostSubject: Re: Outdoor Wood Boiler   Tue Nov 18, 2014 9:47 am

as im not sure of your setup

are you getting flash steam on the coils when its not on a circulating system or on a circulating system

as i believe once you put a pump on it the flash steam should stop on a circulating system the other side is just used via a filling tank pumping into a backup tank or in some cases a central heating system using the method of a plate exchanger on the closed loop system of central heating you also need to put a pump on the central heating side where the plate exchanger is which then can be controlled by another method not by using the boiler pump
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Rebootag



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PostSubject: Re: Outdoor Wood Boiler   Fri Dec 12, 2014 7:24 pm

My furnaces burn green wood smokeless also... i have used it to quelsh temps myself...  I have a boiler in planning stages... welll really waiting for material money.  Mine will use exhaust heat from the in-ground rocket furnace that heats my house with forced air via convection (2 4" ducts) and also circulate to the storage tank via convection.  I'm a big fan of power independence so all my designs use convection... no fans or pumps "allowed" in my work .. :)

My greenhouse has the same furnace setup.
 I love what you're doing and nice job so far!
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