outside wood furnace hydro

[mbk]

 i been workin on an off on this and alot of other projects over this last fall and winter its a furnace to heat water for heating radiant heat and water to air heat exchangers that goes in air handlers on forced air heat it also will have a water to water heat exchanger in it so the domestic water will be heated i still like some ive got most the welding done i need to get the pumps hooked up and insulation on the water jacket then put the sheet metal on and little roof itll look like an small out building what ive done is look at a few furnaces and made this after about three different units here are some pictures of what ive got so far i tryed this earlyer but it didnt go through maybe itll work this time

[mbk]

 ok good it worked this time i prolly wasnt doing something right the last two pictures wasnt for the stove one was my windturbine the other was axles i got last fall for a 17 or 20 foot mill if their big enough ran out of time over the winter to build them yet

[fabricator]

You are going to want to make a smaller screen to go over your grate, all your hot red coals will fall through into your ash pit, you want those coals as the fire bed.

[mbk]

yes it does look a bit wide between them ill have to make it like you said it does have a forced draft blower in the bottom the pipe goes out the back lowwer end to a or what will be a blower out side of the water jacket so ill have to leave some room but not as much as is there now thank you for your response

[tecker]

I like the round fire box .Be fore you get too committed to the over all design take a look at a rocket stove . A long fire box and air entering from the bottom is a sure way to get a clean burn . I think a  support is needed for the grate it will sag and cause the burn plate to deform . Round is a perfect match for copper as the 1/2 comes in coils and will just sit tight when guided on to the form . The small stack is interesting you might get some cooling if you added another barrel to the flue and went for some exhaust gas back in the fire box .Nice ideas it would be fun to watch you heat exchange go together . Don't mind the suggestions I could ramble for days I have done nothing but ()(&) around with my stove all winter .

Good luck with your build.

[12AX7]

Hello

I've never constructed a wood burner from scratch, but I have played with a few.

I inherited a wood stove that had most of it's fire brick busted.  I thought "great, less heat will go up the stack" and I removed all the brick.

Yes!  much more heat was thrown off the stove, into the room.  However, it was a constant struggle to keep the fire burning.  Had to move around the coals, and play with the air vents.  Fire would go from cold to very hot, right back to cold.

It seemed to me that the problem was containing the heat to support the burn.

Relined the burn box with fire brick, and my self made problem was corrected.

So, with that said...   Are you planning on lining your burn chamber with fire brick?

All the outdoor wood burners I've looked at (two or three different manufactures) had some sort of liner.

The heat/water exchangers were tanks (opened, to prevent build up of pressure)on top of the burn boxes, how will your heat exchanger mount to your round burn box?

In addition, they all had a blower to control a forced draft (inter locked) to the door, you're planning the same?

I've an old cast iron bath tub that I've saved with the thoughts of using as a burn box for an outdoor wood burner, just one of a thousand shelved projects!

Looks like a good project!

ax7

Mark

[mbk]

hi tecker yes there was a few with round fire boxes i saw and i had an underground 500 gallon propane tank so i washed it out a few times with soap and water then filled with water and cut it its 42 inches long and the water jacket is 48 inches long for the heat changer im still thinkin on it for the domestic hot water to put it around the burn box or to put it on the back side between the burn box and the water jacket there is about 6 inches if i coil it and let the heated water in the jacket heat it im not sure though if it will get hot enough just settin the copper in the water tank or if i do need to wrap it around the burn box thanks for your reply

[mbk]

tecker sorry i just remembered what you said about the support for the grate i do need to put brace in it i made the grate so it can be taken in an out too so i can change them if need be to burn different types of material

[bob golding]

in my experience if you are burning ONLY wood you dont need firebars. wood stoves burn better if you just have a bed of ash. the other thing is to put a diffuser in the top of the firebox so that the smoke gets reheated on its way to the flue. i have an old railway guards van  stove that was designed to burn coal. i also have a victorian range up at the house which was also designed for coal. i have found that they both burn much better on wood with no fire bars. if you are also going to burn coal as well you do need firebars.

[mbk]

hi 12ax7 on the fire brick i was wondering the same thing being that the whole burn box is surrounded by water all except the doors their self i didnt know if the fire brick would hurt the transfer of heat or help by keeping the fire brick hotter longer an helping the water to heat better   on the water tank this one will be vented too at top so it will not build up pressure the heat exchanger will either be wraped around the burn bax or coiled up just between the burn box and the water jacket wall the water jacket should hold around 200 galons of water this water will be not domestic its for the house an shop heat it will be pumped to house an shop where another water to air exchanger will be for heat  on the draft blower itll be piped in the burn box down lower in back of burn chamber under the fire in ash pan part and out the back of water jacket with therm control aqua stat controll it

[fabricator]

That is why wood boilers are terrible smokers, they burn wood very inefficiently, because they burn cold.

Every square inch you cover with firebrick detracts from heat transfer efficiency, so it's a trade off get a more efficient burn with a brick lined pot or get more heat into the water and get a dirty, smoky burn.

[Ungrounded Lightning Rod]

Of course you could burn the wood hot on the firebrick, then cool the exhaust and heat the water with plumbing in the stack.  (Watch out for boiling - unless you WANT steam power or heat.  B-)  )

Once the fire is out the firebrick will still provide some heat for the water until it cools off.  So you don't lose your BTUs.

Downside:  You're dealing with VERY hot gas.  So you are now in "making a boiler" territory.  Tougher engineering.  Explosion risk.  Government inspection requirements.

[12AX7]

Hi

If you haven't already, I'd suggest you read through the several last threads about woodburners/ heating with wood.

Check out "Heating with wood" by Coldyny

TomW posted a good reply in another thread (thinks it was "air tight wood stove"

here is his post..

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I claim no status as an expert.

I grew up with wood heat folks heated with a coal stoker furnace and after about say 6 or 8 years old it was my chore to see the coal feeder chain was kept full of appropriate chunks.

Subsequently I heated with wood my whole adult life except a winter in a warmer climate.

After a lifetime of burning cordwood I will share with you a couple of things I believe:

To properly burn wood cleanly and get the most heat you need to let it get plenty of AIR. Choking off the air supply will indeed extend burn time but allows a lot of unburned fuel [gases] to escape to the atmosphere. This creates smoke and gunks up the chimney and has led to the demise of many inattentive would be wood heat users.

Heating with wood is NOT cheap or easy. After you put your sweat into gathering, cutting, stacking and seasoning firewood it just seems stupid to not get the heat out of it that is in  it.  

My personal wood burners have ranged from an open hearth stone fireplace [major fuel hog] to my current stove 30 years or something old and capable of being closed up enough to extinguish the fire. A couple stoves I used leaked so much air they lit the room at night through the cracks. That type never needed a chimney cleaning because they supplied enough [too much] air to the fire so it burned clean and hot. These required a flue damper to control the air going through the system. I also think it helps retain some heat that would otherwise go up the flue. This heat retention is obvious if you stand there and go from damped to open with a well burning fire.

I still use the flue damper on the current stove that is more or less "air tight" it vents to a Class A clay lined masonry chimney. I find this same heat retention seems to be there. If I am not careful this stove is prone to gunk up the chimney if you pinch off the combustion air too far with a load of even bone dry wood. We use hardwoods like Elm, Oak, Hickory, Hackberry and Cherry exclusively cut and dried at least a year in the open shed so it is dry.

If I were to build a stove it would include an afterburner air inlet to assure full combustion in a smoke chamber at the top of stove. Or just go for a down drafter that draws flue gases through the coal bed before it exits.

But, the very best way would be a massive built in unit with multiple small flues like 3" pipe running through a mass of material to  the flue. Burned hot and fast I believe this would be the very best method for a ground up heating system for solid fuel.

Well, there it is, rambling but my thoughts. Likely not what everyone believes but there you have it.

I do like heating with wood. Do not be fooled into thinking it is a free heat source.

We own and maintain 2 Stihl Chain saws, [a 16" and a 20"], a pickup, an ATV and trailer, a wood splitter. As well as consume a fair bit of fuel, oil and chains. All for the "free" heat from our "free" 400+ acre timber.  Takes a good few hours of real work to do, also but I wouldn't do it any other way, as long as I am capable.

Tom

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He pretty much says it all.

Remember third grade science.  Fire needs three things.  Fuel  O2 (oxygen) and HEAT.

If you take the heat away before the burn is complete your fire goes out!

I've got a nice LONG story about being a "fireman"  running two VERY large boilers in a furniture factory in WI.  Buildings were pre-1900 Lots and Lots of windows, everyone single pane, took up two/three city blocks and not ONE OUNCE of insulation.  gas fired, but also equipped  with the org. sawdust feeders.  

But like I said..  it's a long story!

Keep that fire HOT!

ax7

Mark

[tecker]

My stove is on the website I don't have the insert for the Stove up yet but Click on the pic and there's some of the original videos I have been setting up a rocket grate that I 'll rush up and get the project page up    www.rspc.info    I'd like to do some finish stoves from other folks if your amind .

[BigBreaker]

Taking heat out of the fire box is not the way to go, IMHO.  You want the fuel gases to get hot and stay hot for as long as possible before liberating their heat.  That means an insulated fire box and a long, heat retaining flue before doing the heat exchange.  Some of the gasifier burners have ceramic lined passageways to let the gases burn as much as possible, as hot as possible before heating/boiling water.

Always have a pressure relief valve in your hot water system.

[WoodstoveWizard]

Hi mbk,

looks like you have put a lot of good work into this project. I wish I was as confident with my welder - it would make planning bigger projects much easier.

As other people have mentioned, extracting heat directly from the burn chamber isn't a brilliant idea. To burn cleanly all of the fuel and wood gases need to get really really hot. This helps split the gases down to the absolute simplest molecules (carbon monoxide etc...) that then finish burning cleanly once the temperature drops.

If you can't maintain high temperatures for at least the first stage of the burn process I suspect that you will struggle to get a stable and clean burn.

If you can, I'd investigate ways to extract the heat after the gases leave the main burn chamber. At this stage the combustion is much less temperature dependent and you can safely extract as much heat as you want, especially as you are using forced air so are not dependent on flue draft to maintain the drag through the fire.

I'd consider routing your flue pipe down again and jacketing it with an outer sleeve of water for your heat exchanger.  The main burn chamber I would line with firebrick or dry sand and then insulate around the outside with a big load of perlite or vermiculite.

It is a bit hard to tell from your photos, but you say you are trying to make it look like a small outbuilding? If you gave it a pitched roof your heat exchanger, to remove heat from the flue gases, could be tucked into the roof itself. I'm still thinking how best to do that - perhaps a copper coil inside the length of flue itself? You would want to figure out some way to remove the coil for occassional cleaning, and to put in plenty of pressure release valves!

I hope you don't feel this is too negative on your current designs, but problems of combustion efficiency have been plaguing wood boilers, especially outdoor ones,  for year. With just a little more thought and work you could have one that runs with fewer problems, less smoke and more efficiently.

All the best

Mike

[JW]

Hi Mbk,

 Nice welding by the way. One thing to consider, is somesort combustion air preheater. This will solve the smoking problem instantly. You mentioned a draft booster fan, this can make it easy to do. Run a section of auto exhaust pipe into a hot part of the combustion chamber then feed air to the burner, using that heated air pipe.

JW

[REdiculous]

That seems totally counter-intuitive to me.

I can see how warm air might be less of a shock to a small/cold fire but other than that I can't imagine how it could be better. Cold air is denser and the more air you feed a fire the better (within reason)...

So how does heating the air help exactly? I don't get it.

[JW]

Hi,

check this link.

http://www.energysc.org/downloadables/preheat_combustion_air.pdf

do a search for "preheat combustion air" and you will get more info on this, the heat can be derived from the exhaust stack, or alternatly directly from the combustion chamber.

With internal combustion the use of intercoolers is benificial. But with external combustion things are a bit different.

JW

[KilroyOdin]

Greetings, nice work. have thought about building a down draft gasifier. Burns clean and uses less wood for the same heat.