Wood burning workshop heater- ideas ??

[Renze]

Hello,

I just decided that the oil heater (burning old engine oil) has to make place for a burn-all heater. On a cold day i can burn 40 liter of old engine oil, which is 1/3 of my annual rate.
We're surrounded by forest, giving plenty of wood to burn.

Now my question is: What is an advisable firebox to start from ? I dont want to take a 208 liter oil barrel because it will fall apart from the heat.. I need to find a big pipe with a wall thickness of at least 8 mm i think...

Would the firebox pipe be put horizontal or vertical ? What's the minimal wall thickness, and how do you seal off the door, to prevent eye irritating gases to escape when you just lighted it ?

I need to haul a big load of scrap this week, so when i am at the scrapyard, what kind of tanks, barrels, boxes do i need to look for ???

 

[RonMar]

Well if you want something that will last, you will probably want 1/4" or more wall thickness. A tight Seal around doors and fittings will be good for controlling the fire and heat output. If your fluepipe is installed correctly, you should never really get any fumes in the space being heated because as soon as it starts to make heat(as soon as you light fuel in it), the flow of hot gasses up the chimney keeps the stove under constant vacume. You want the path of least resistance to be up the flue and not back out the door.

Most woodstoves use a cast iron door. On the inside of the cast door around the edge is a molded groove into which is glued (with high temp sealant/cement) a braided fiber seal cord made of high temp fiberglass. You can buy this seal material in various diameters at most places that sell wood/pellet stoves and their supplies. If I was to make a stove with a plate door, I would weld a channel around the inside face to accept such a seal and design the hinges and latch so that the seal would be held flush against the front face of the stove around the opening. To simplify fabrication I would incorporate the combustion air control into the door also. My goal would be to make it air tight. This would give me better control, even to the point of being able to put the fire out by starving it for oxygen.

If you have some heavy walled pipe to use as a body, it would probably be easiest to put the pipe parallel to the ground with plate welded onto each end to seal it. The hard part will probably be getting a heavy walled pipe of sufficient diameter. I have attached a sketch that depicts a 20" dia pipe, 35" long with a 6' flu pipe. Unless you make the door round(harder to fabricate the seal groove), you can only really fit a 12" square opening into an end and still have room for the door to seal. The legs that support it could also be incorporated into the end plates. My drawing shows flue output on the top rear with an internal baffel that holds the gasses in the stove for a little while(more complete combustion and more time for heat transfer). You could also add internal heat exchanger pipes right above the baffel that run the length of the stove. These could be fed room air with a small blower to aid in overall efficiency of heat transfer to the room. At any rate, the baffel should be removeable to clean up there as material that falls back down the flue will build up there. If you added heat exchanger pipes, they would also need to be cleaned occasionally. You also need some heavy grating or fire brick in the bottom to get the fuel up off the bottom(this will extend the life of the steel shell) and allow a space for ash to collect. Preferably something easy to clean out.

I have heated with wood for most of my life. In my current home, we use wood for about 90% of our heat. We just recently replaced our small wood stove with a pellet stove. I am getting to the point with my land that the annual supply of thinned trees and downed/blowdown wood will not supply my annual needs. So if I have to import wood, it might as well be in a form I don't have to put as much work into processing. The small woodstove is heading for the workshop garage to provide heat there. My land will supply enough wood to heat that space. It is very similar to the drawing I have attached, but square and made of 1/4" plate. It is lined on sides and bottom with firebrick and the steel is just as sound as the day it was produced. It is pretty old, one of the first stoves that Country woodstoves produced. I plan on adding heat exchanger tubes and a blower to it. You might also try looking at some of the manufacturers online for ideas.

Good Luck.

 

[bobodu]

Old air compressor tank,gas hot water heater,some scrap plate and a cut up oxygen tank.

Outside test burn to get rid of the old paint. Eats lots of wood but also doubles as a forge!! Intake air is controlled by a sliding plate under the grate.Efficiency really doesn't concern me because I have lots of wood and when it's really cold...the fire NEEDS lots of pokin' anyway...although,I'll probably add more tubes to the heat exchanger next year.She will keep the uninsulated,drafty 24 X 40 foot barn tollerable on a 0 degree day and toasty when it's 32 and above. /forums/images/graemlins/blush.gif

 

[Renze]

Ronmar, i like the idea of you baffel... I think i shouldn't be afraid of backdraft of hydrogenious gases when the exhaust gases only go upway.

In our weekend bush hut, that me and my friends use to barbeque and drink beer in the weekends, we have an old coal stove, that has a dual gas opening in the top of the heater, which attaches to a kind of air radiator, the radiator has its opening into the chimney pipe about 1-1/2 foot lower so the air has travels up to the top of the heater, then to the lowest spot of the radiator and then up again in the chimney...

This gives a good efficiency when the heater is hot, but when the chimney pipe is cold, the gases leave the heater through holes in the front door....

I was just thinking, maybe i need to make a baffel/radiator that sends the hot air down lower, before it goes into the chimney pipe, with a bypass valve that dumps the combustion gases directly into the chimney allowing the gases to travel straight upwards when there is not enough heat in the chimney to give enough draft.

How does that sound ? would it be worth doing ?


The stones for heat protection of the bottom part of the heater, could i just pour cement in it, or throw some bricks there ? Or do i need to get the special stones from the supplier of the horse shoe oven of my brother ?

Would a burn-all heater, just burn everything ? Also the general farm waste like bale plastic and feed bags or would this cause a thick sludge on the bottom of the heater, that doesnt burn away clean ?
The more fuels it can burn, the better..

Does anyone have some links to websites for me please ?

 

[RonMar]

I wouldn't reccomend concrete as it sometimes holds air pockets that wil explode when super heated. Concrete would also breakdown and turn to dust from the heat. You could make a simple base grate from say 20MM square bar stock steel that lay across the stove with a couple rails that run the length to weld them all to. Kinda like a railroad track with crossties, only turned upside down. You could space them 20-30MM apart. This would get the fire up off the bottom of the container and allow ash to fall to the bottom. Just make it easy to remove out the door so you can remove ash from the bottom of the stove from time to time. With a hot enough fire, you can burn just about anything but different combustables leave different residues. With a hot enough fire plastics burn nearly completely but the gasses produced arn't the best for the environment.

 

[Renze]

RonMar, i see what you mean... just a kind of grill roast /forums/images/graemlins/wink.gif to keep the fire off the floor, and to allow fresh combustion air to come up from under the fire...

What about the fresh air intake from outside the building ? I hear people talk about it, but does cold air intake from outside, prevent warmed air from inside the workshop being sucked via the heater, out the chimney pipe, causing the building to suck cold air in through unsealed openings in the building ?

About plastics, bale plastics, when burning hot enough, hardly gives any smoke. What they do with most waste after collecting it, is spending a lot of Diesel to drive the garbage trucks and then burn it in a waste oven in the other end of the country.... I've seen documentaries on TV about people that had sheep at around 1 km from the oven. 50% of the sheep dropped dead from the extreme concentrations of residues in the grass they ate, because of the millions of tons of waste they burn annually, at one single location...
Off course these waste ovens are environmentally friendly, our government has a scientific report from their ministry, remember ?? /forums/images/graemlins/ooo.gif

sure it will be pollutant when the fire isnt hot enough... But pollutant it will be, no matter in what oven it is burned, the only difference is the amount of diesel used to truck it 200 km away to the state certified waste ovens. /forums/images/graemlins/smirk.gif

 

[Renze]

Oh by the way: i think i can use barred panels from manure pit roasts of our old piglet barns /forums/images/graemlins/wink.gif

 

[Nomoregears]

I've built quite a few wood burners being a welder by trade. Going thicker is not always better. The expansion and contraction can kill a stove quick. My best stove was a furnace made with 1/4" steel. I made a sizeable fire box that I was able to line with firebrick. About 2" away from the wall of the stove I put another layer of sheet metal. I hooked up a squirrel cage and forced the cool air across the stove.This takes the heat away from the stove and extends it's life. I had duct work and a plenum to attach to the top of the stove. Between the fire brick and the area on the top of the stove that had sand in it, I was able to heat 2900 sq ft of house very easy. You can make this as elaborate as you want with thermostats and limit switches for the fan. Even put a hot water jacket in it for having hot water for a pressure washer.
I've been looking at big natural gas pipe for my next wood burner. A 2' dia. firebox with ends welded on should do the trick. Baffles should be loose,set on rails inside. Doors can be plate steel, thin firebrick and a heat shield. The heat shield set off the door about 1" will keep the door from warping.
As far as the cost of the stove, it depends on your ability to scavenge. Steel stoves don't last forever due to the corrosive nature of the wood smoke. Wood is a renewable source of energy.
Good luck, I like the idea of a forge in the stove.

 

[RonMar]

</font><font color="blue" class="small">( What about the fresh air intake from outside the building ? I hear people talk about it, but does cold air intake from outside, prevent warmed air from inside the workshop being sucked via the heater, out the chimney pipe, causing the building to suck cold air in through unsealed openings in the building ?)</font>

Your description is correct. Without a feed of combustion air from the outside directly to the stove, the stove will draw air from the room and exhaust it outside via the chimney. Since this lowers the pressure in the room, that air is made up from elswhere via leaks in walls and around doors and windows. If the structure is well sealed, this can even impede the stoves ability to function and be hazardous to the people inside. It is a installation code requirement in this country on pellet and wood stoves that when installed in certain types of homes that outside air be provided to feed the stove directly.

 

[jimmysisson]

If you do use the wood burner to heat water be aware of the power of steam - always have a way for the pressure to escape whether you're there or not, or using it or not.
After 30 years burning wood in the same iron stove with no damage to the inside base liner, I'd say that 3" of stove ashes will adequately protect the iron from warping or corroding. I just take the ashes out in the summer so humidity doesn't activate them at all. Then in the fall, a few small fires builds up the ash level to safe amount again. You can also use sand (not highway dep't. w/salt) which works great.
Jim