outdoor wood burner who has built one

[TWD]

Hi TWD,

You have several options, which one is best depends upon how you use your shop. If you use the shop frequently (every day, for example), heat in the floor is VERY nice. Infrequent use, then perhaps a coil with a blower. Radiators are another option but i doubt there are many shop arrangements that these would make sense for.

An OWB is nice for heating a shop if you are also using it to heat your house or if your shop is large and you are using it every day. It would normally be a bad solution if the situation was that OWB was used only for the shop which was occupied one day per week.

Feel free to PM or give more details/questions here if that is not considered thread hijacking.

Ken

Hi Ken, great information.

Right now the shop would be used only a couple times per-week for hobby usage. But in the next couple years I plan to move my office from the house to the upstairs of the garage, and heating that daily would be awesome :thumbsup: and probably required in winter

We also only have a wood stove for our house, so having the OWB to replace that or ??? would be great too. We have a full basement so plumbing most anything is very simple. We also have an on-demand propane water-heater... replacing that or additional heat/optional with an OSB would be great too.

I may just have to do an OSB as a project ocne I get my shop back to fully functioning after the rebuild.

Do you have any suggested resources?

 

[yomax4]

Most regular home type wood stoves have the pipe nearly flush with the top of the stove. Most all of the heat and smoke goes right out the pipe. With the OWB many builders extend the pipe well down into the fire box so the smoke has a hard time exiting the stove. While it swirls around it gets re-burned. This is what these guys call secondary combustion. To me it creates creosote but the creosote burns too making a very hot fire. If you decide on an OWB, Remember, It is at it's best when it is active ie: Draft Open, Pump running and the fire burning. If you have long lapses in calling for heat it will not be that efficient and it will smoke a lot. There are some very good plans for building a simple OWB on e-bay for $30.00 just search "outdoor wood furnace"
I have a life supply of hardwood and a friend with a sawmill who gives me as many 10x10x6 oak rejects as I can haul. If you have to buy wood, I would skip the Boiler. My boiler uses a simple waterheater thermostat to tell the draft fan when to kick on. You can use an aquastat too but they are $70.00. If you build, I would recomend and ash pan area below the grate. Mine blows air up into the fire box via the ash pan area.. OWB's are cool to build and save a ton of cash...I noted that I could build an 8000sqft OWB for $1000 or I could buy one for $7000.00.

 

[badbowtie]

Most regular home type wood stoves have the pipe nearly flush with the top of the stove. Most all of the heat and smoke goes right out the pipe. With the OWB many builders extend the pipe well down into the fire box so the smoke has a hard time exiting the stove. While it swirls around it gets re-burned. This is what these guys call secondary combustion. To me it creates creosote but the creosote burns too making a very hot fire. If you decide on an OWB, Remember, It is at it's best when it is active ie: Draft Open, Pump running and the fire burning. If you have long lapses in calling for heat it will not be that efficient and it will smoke a lot. There are some very good plans for building a simple OWB on e-bay for $30.00 just search "outdoor wood furnace"
I have a life supply of hardwood and a friend with a sawmill who gives me as many 10x10x6 oak rejects as I can haul. If you have to buy wood, I would skip the Boiler. My boiler uses a simple waterheater thermostat to tell the draft fan when to kick on. You can use an aquastat too but they are $70.00. If you build, I would recomend and ash pan area below the grate. Mine blows air up into the fire box via the ash pan area.. OWB's are cool to build and save a ton of cash...I noted that I could build an 8000sqft OWB for $1000 or I could buy one for $7000.00.

Can you give some more clues on how you can build one that cheep I am looking and figure I am going to have 1400 hundred in just steel. How thick are you using I could do it if I used 1/8 for the comlete job.

 

[yomax4]

My figures on cost are my situation. I have friends with a machine shop who rolled me a 36"IDx 54"Long X 3/8" thick cyllinder for my fire box for $80.00. The water jacket is 5/32" and it is square. Other than that all of the Suppport Angle iron was 1/4" and Gussets were 1/8. Then I had about 20' of 1" x 1/8" square tube. The stove pipe was a piece of 6' x 6" that was $8.00 at a recycle center. If you can buy your steel at a scrapyard,You can save 1/2.. I think my cost on the structure was about $750.00.. Anyway I used a blower from Grainger and a water heater thermostat. I bought a Taco 007 pump to pump the water to the house. I also ran an extra length of 3/4" pex to a coil of copper tube that is siliconed into my water jacket.( i can explain ) I hooked the return to a check valve and a ball valve so when it's time to add water ( which is evey 4 days ) I only have to flip the ball valve to fill. Plus I am using soft water to fill my stove. Anyway, I have 2 pumps now. 1 to pump water into my shop and 1 for the house heat. Sounds simple but I have done a lot of work to get here, Let me know if you have any questions..

:thumbsup:

 

[SpringHollow]

You have to add water every 4 days? wow. I have an open system and only have to add a couple of times per season, a few gallons each time. I wonder what the difference is.

Ken

 

[Egon]

[QUOTI wonder what the difference is.
E][/QUOTE]

Temperature and volume if it is an open to air system with no leaks on the distribution side.

 

[yomax4]

I just turn the valve for a few seconds every 4-7 days to make sure it is toped off. It has an overflow and i like to keep it full to prevent rust as long as I can. I also run mine at 180-190 degrees in the cold part of the Minnesota winter and that is hot enough to evaporate a little water. Im sure I have no leaks. I have had every problem under the sun working out the bugs but this is my second year with no troubles. The bigest problem I had was with using "Shark Bite" fittings. Not long after install, They leaked. I ended up removing a lot of plumbing and re-did it the old fashioned way. That was only one of many minor troubles that had to be worked on out in the cold.

 

[SpringHollow]

I have used shark bites in lots of situations including my boilers and my family's and friends boilers with no problems. Did you have them pushed in all the way - it can be hard sometimes with the stress on the pipe. My friend did install one that leaked but when i came over to look, i saw that although he thought it was pushed all of the way in, it was not. I have used them on pex, copper, and polybutylene with no problems so far. I have not tried some of the other brands.

Keeping the boiler completely full of water for rust prevention is a very good thing.

Ken

 

[yomax4]

Yeah, I didn't know much about shark bites and I may have tried to tighten them too tight. It would leak a little, I would tighten a little, Leak, Tighten. Break.. It was cold out and I just wanted to get the leaks done. They are a cool concept and I would try them again.

 

[smiley]

I was thinking about installing a plate steel stove in a cheap tin shed. Then ducting the shed air into the basement and using floor grills to let the heat rise. My lot slopes down favorably on the side where I'd do it so blowers might not be necessary with a big enough duct.

I've seen 3 built this way. 2 in garages 1 in a house. 2 were old wood furnaces in old insulated truck closed van bodies, the other in a steel shed. All were forced air though. My friend who heats his garage this way hasn't had any problems. It's about 8-10 ft from the garage and isn't pretty, but he has insulated ductwork both for heat and return air.

 

[jimgerken]

Yomax, why do you recommend building one with as much water volume as possible? It seems to me that makes it inefficient. The 400 gallons of water out in the yard surrounding the burner is doing nothing to heat my shop or house, its just loosing heat continuously. Why wouldnt say 50 gallons surrounding the burner work just as well? I'm not saying I know enough to argue with you, just curious. Thanks.

 

[SpringHollow]

If the water volume is too small (and i would say 50 gallons is for most fireboxes), your boiler keeps cycling - just gets burning and you shut it off. It also makes it easier for the boiler to overheat (boil over) when you no longer need heat. There is still a lot of residual heat in the coals etc.

If the water volume were way too large, the cycle times could be so long that the fire would go out on a well made boiler. The volume would have to be very large for this to occur.

Ken

 

[chickenman]

why not put the water where you want to heat and just run tubbing through the furnace?

 

[SpringHollow]

If no water reservoir, you waste a lot of the heat in your coals. Also, there is a slight chance you would overpressurize the closed loop to the house. A very acceptable design is to have a smaller water volume at the boiler and an extremely large water storage mass located elsewhere. In this design, typically a new fire is started each day in the boiler. Then the boiler burns continuously until the storage water is brought to temperature at which point the boiler shuts off for the day. Personally, i like starting only one fire per season instead of every day.

Wood boilers are not like a gas/propane boiler which cycle instantly and have little thermal mass in the combustion chamber.

Ken

 

[yomax4]

I have sold equipment to all of the major OWB manufacturers, Central Boiler, Wood Dr. Taylor, Heatmor etc. It seems like between 250 and 350 glns is what they have found (with the research dollars they have spent) to be most efficient. That way, You can have your OWB over 100' from the house and pump hot water there and back without worring about it getting too cold. My water jacket heats a copper coil that I run my potable hot water through for free hot water that never ends. In most winter cases at least where I live, In the winter time your furnace will cycle and call for heat often enough that your fire will never go out. As soon as the water temp drops a few degrees the fan kicks on and fires everything back up. I start 1 fire in Sept. to heat hot water and a little house heat but it never goes out until May. :thumbsup:

 

[SpringHollow]

My boiler is about 145' from my house. I only lose at most a couple of degrees in temperature over that distance since i have reasonably well insulated pipes. I added thermometers before and after heat exchangers etc because i like to see what is happening. You can get a crude idea with an IR thermometer which are pretty cheap at places like Harbor Freight.

Some boilers have as little as 130 gallons, a few even less. Lots of factors come into play - size of firebox, heat demand of the house, how efficient the boiler transfers its heat to the water, how air tight the combustion chamber is, etc.

Ken

 

[yomax4]

That is correct. The sticker is when you want to heat more than 1 building. I heat a 4500 sq ft house and a 1000 sqft shop. My stove works it's butt off to do that even with a large water tank. The house is a heat exchanger in the plenum and a closed loop floor heat in the basement. Same with the shop. Closed loop floor heat. Water heater is just a hot water storage tank as it has a pump hooked to an aquastat set at 140 degrees. Pumps a loop from the boiler back to the waterheater. From all of the plans and boilers I have looked at it seems that the larger the heat requirement, The larger the firebox and water jacket. I suppose there are some stoves out there that work just fine on less water but I have no complaints about mine that's why I bring up the water capacity. If you build one, Do the research 1st and enjoy..

 

[SpringHollow]

I heat my house (heat in the floor and radiators upstairs), domestic water, ice melt system, and barn/shop (heat in the concrete slab) with the OWB. They are all isolated from the boiler by two heat exchangers. The barn/ice melt loops are filled with antifreeze. For burn times, the size of the firebox is more important than the volume of water assuming the water volume is reasonable. The firebox volume along with your heat load and the efficiency of the stove basically determine the burn time you will get.

But i agree, there is not much advantage to having a small water volume for most systems.

Ken

 

[yomax4]

I think my firebox is 38" x 54".x 3/8" thick cyllinder shaped. Seems to do the job but I wish I would have made my door a little larger. Mine is 18" square and that seems like a big door but when I throw in 12 - 14" round logs, Gotta watch the fingers.
I like the ice melt program. I wish I would have done that. I have a 14' apron in front of my shop that could use a loop of heat. What type antifreeze did you go with? I think I could have used Ethylene Glycol like the autos use for my shop floor but I was talked into Propylene Glycol at triple the cost.

 

[SpringHollow]

My ice melt system is in the gravel walkway down to the house (reasonably steep). I added it when i had to dig a trench in that path anyways.

I used heating system antifreeze which is the non-toxic propylene glycol with corrosion inhibitors, etc. It was not that much more expensive at a heating supply company. It does not take much ethylene glycol to kill a dog so i think it is worth it.

Ken