outdoor wood burner who has built one

[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