Barrel Stove Questions

[Salmonberry]

I researched the old threads for answers, but now I have more barrel stove questions. For anyone with experience making or using a barrel woodstove, any help would be appreciated.

1) How much less efficient is a barrel stove than an EPA non-catalytic stove?
Are they like an old Franklin stove, or better than that?

2) Will stove brick in the bottom help with preventing the metal from thinning?

3) Would I be able to make the stove myself?

4) What type of tools would I need?

5) Any other problems that I don't know about?

Thank you. You guys are great.

[JAK]

1) How much less efficient is a barrel stove than an EPA non-catalytic stove?
Are they like an old Franklin stove, or better than that?
- You can make one as efficient, or more efficient, or less efficient.

2) Will stove brick in the bottom help with preventing the metal from thinning?
- Yes. It will also increase combustion temperature, but also the flue gas temperature.

3) Would I be able to make the stove myself?
- Yes. If you want to ensure high efficiency you will have to be able to measure effiency, and you will likely have to design and redesign and build and modify and rebuild and modify until you get what you are after. Some people are better at the theory. Some people are better at the craftmanship. The most important thing is passion.

4) What type of tools would I need?
What materials do you have? What tools do you have? You could do it with a welder. You could also do it with clay. There is always more than one way to skin a cat.

5) Any other problems that I don't know about?
Yes, and probably even more that I don't know about.

I would suggest you research rocket stoves as well as barrel stoves. I am not suggesting that one is better than the other but that there is really a continuum and the same principles apply to both and that ideas from one can be applied to the other. Also, as I alluded to earlier, you will need to be able to measure efficiency if you want to know that you have achieved it and see if you can improve it. Research how to measure efficiency of a stove and that will also help you build it. It's like feedback. Another suggestion would be to learn by building small 1/2 scale or 1/4 scale models, so that you will learn faster. The best design in 1/4 scale model will not be the best design for full scale, but you will learn faster.

Take the following measurements when testing your stove:
1. Use standard lumber for testing and always use the exact same weight, dimensions, and moisture content so you can measure improvement more objectively. It might be helpful to use lighter fluid or vegetable oil to start it consistently. Use it consistently.
2. Measure or estimate the moisture content of the wood. [%moisture by weight].
3. Measure or estimate the total HHV heat of combustion of your fuel. [BTU].
4. Load the fuel and starter in the same way each time, or as close to it as you can if you have changed the firebox design.
5. Record the room temperature, pressure, and humidity.
6. Record the following temperatures every 10 minutes or so:
6.1 Combustion chamber temperature
6.2 Flue entrance temperature (where it leaves the stove)
6.3 Flue exit temperature (where it leaves the stove)
7. Record the flow rate exiting the flue.

The last one will be a bit tricky and the most prone to error. Air flow rate can be measured different ways, but it is complicated because you don't want to disturb it to much, and you don't want to stick expensive instruments into hot flue gas. Rather than mess with pressure readings I would device some way of measuring velocity in the middle of the flue and then assume some sort of velocity profile, probably one for turbulent flow. This is the data you need. Actually it is not everything you need. You would also need to know how much CO and other unburned combustibles have escaped without burning. This is important, but difficult. I would suggest just making observations every 10 minutes about the colour of the smoke. Combustion temperature and flue entrance temperature will offer clues. Also, you should expect that most volatiles to escape in the first part of the burn while the fuel is heating up and the moisture is evaporating.

Calculate efficiency as follows (assuming complete combustion):
Efficiency = 100% - (Heat of Flue Gas) / (Heat of Combustion of Fuel)

You will need to do some research to determine the Heat of Flue Gas. It is based on temperature and flow rate of the flue gas at flue exit, but you also have to determine the composition, which is lots of fun actually. There will be air, mosture, carbon dioxide, and everything else which you can just call fly ash. Roughly half the moisture comes from the moisture in the wood, and the other have comes from the combustion of hydrogen in the wood, and a little comes from moisture in the air. Once you have done one calculation to estimate the efficiency as best you can, you will find that improvement come from having about 150% excess air, a combustion temperature in the combustion chamber of at least 500F, and a flue exit temperature of 180F to 225F. The flue entrance temperature can vary, but the trick is having enough firebrick insulation and baffles to get a good combustion tmperature while still getting most of your heat from the stove top. If the flue entrance temperature is high you will need a longer stovepipe in order to extract the remaining heat and get the flue exit temperature down to 225F. If the flue exit temperature is too low you will get condensing water vapor and a lot of corrosive fly ash and possibly combustible creosote with it. You probably only need to do all the calculations once, and from there just try to get the temperature and flow rates to where you think they should be. The hard part will designing a small stove to run efficiently through an entire burn cycle without requiring too much fuss and attention.

[Ole Man Legrand]

I bought a kit and made the stove myself. You will need a sawsall or a cutting torch screw driver and wrenches.I put about 4 or 5 inches of sand in the bottom to keep it from burning out.I used it a long time untill I could afford an upgrade.

[Cyngbaeld]

Never made one, but have used a few. Seems like they put out more heat than the franklin stove I had. Lots of folks in Alaska used them when I was there back in the '60s.

[HermitJohn]

Two barrel version (one barrel on top) more efficient than one barrel, but have a chimney with good draw (best with any stove). I am still using old Sotz airtight kit that I got in early 80s. I have used it on big barrels, little barrels, and at present on a rather heavy duty old water pressure tank. Lots of ways to make holes necessary. Cutting torch or ac welder with 6010 rod is nice, but sabre saw or sawsall works ok, and if all you got is a hammer and punch and sharp cold chisel, have at it. Not even that hard to make barrel stove without kit but have to be bit creative and some experience working with metal would be nice.

Oh, I never saw any reason for firebrick or sand. Just layer of ash and small homemade rake to rake coals forward before reloading.

[Salmonberry]

Thanks all for the information. Sounds like I might be able to do it if finances are tight at the end of summer (We are building this summer and you never know what might come up).

Salmonberry