I took a month off making YouTube videos, but I’m back at it. This time, I decided to compare my DIY gasification boiler to a non-gasification commercial unit. As you can imagine, the difference is night and day:
Here’s a picture of the primary combustion chamber:
I also got a picture of secondary combustion occurring, both under the grate, and along the secondary air injectors:
It shows up much better in the video. I hope this gives you some insight into the difference between gasification stoves and boilers and the older, much dirtier way of doing things.
In my latest video, I discuss some very basic stove science, the energy density of wood, and the idea of building a solar powered heater. It also showcases the latest version of my stove calculator spreadsheet.
One thing that I failed to really drive home in the video was a better propane vs. wood comparison. I gave the propane energy in BTU/gal, it converts to 21698 BTU/lb, quite a bit higher than that of wood.
A friend of mine on YouTube, boyntonstu, has a great way to illustrate the difference between heat and temperature. First, I think we all agree a lit match would have a higher temperature than our body. Now, which could melt more ice cubes? That, my friends, is the difference between heat and temperature.
I’ve worked a bit more on my stove calculator, and have added two more calculations to it. Download it here: updated stove calculator. The first new calculation figures out the thermal efficiency based off the temperature of combustion vs. the temperature of your exhaust.
The second is more useful, and figures out how efficient your stove is at converting wood BTUs into usable heat BTUs. This is where the rubber meets the road in your stove’s fuel efficiency. You can use the first calculator on the spreadsheet to figure your stove’s BTU output.
If your stove is burning smoke and odor free, you should see very high efficiencies. If your stove is smoke free, but produces a lot of soot deposition and odor, it’ll be high, but not up to its full potential. If your stove could be named Old Smokey, efficiencies will be fairly low.
So give it a try and see how your stove stacks up in the numbers. It is a very valuable tool in tweaking your stoves and measuring your progress. I hope you find these calculations as useful as I have over the years. I’ll be adding more in the near future. I’m also beginning development on a smartphone app that will allow you to take the calculator with you.
This week’s video is my live broadcast attempt #2. It went much better than the first, it’ll probably take me a few times to doing this to loosen up a bit on camera. Here’s the video in case you missed it live:
The next time I do this, I’ll announce it a week ahead of time so we can get a few people in the chat room and make it more than me rambling in front of a camera. Feel free to join in. Most of my subscribers are into wood stoves, alternative energy, electronics, and outdoor sports like hunting and fishing. If you are interesting in those kinds of things, it should be a fun way to hang out and make friends.
As I mentioned in the video, I’ve been working on a spreadsheet that does some stove / boiler calculations. Here’s the spreadsheet for you to download and try: Stove Calculator.
If you are interested in having something like this as a smartphone app, let me know in the comment section on the above YouTube video. Also, let me know if you are using Android or iOS, so I’ll know what platforms I need to be able to support.
The first week of using my boiler has been very successful. The boiler is very useable right off the bat. Here’s a video that shows some highlights and discusses some future modifications I plan to incorporate:
Since making the video, I have determined that using dry wood makes the extra heat riser pretty much unnecessary. It only required a very simple modification to the grate. Let’s take a look at the grate to understand how my modification works:
Keep in mind that there are two 1″ I.D. secondary air tubes that run in the center on the underside of the grate that extend into the entrance of the secondary combustion chamber. You’ll note that plate with holes welded to the top side but not the bottom side. I noticed that the entrance to the secondary combustion chamber was free of soot at that level, but badly covered with soot on the bottom half:
After making this observation, I added a small piece of the same metal to fit under the secondary air tubes. What was happening was the blower was injecting too much air under the fire, escaping underneath the grate, cooling the secondary combustion chamber, and starving the primary combustion.
This baffle slowed the airflow, increasing the temperature under the grate, and the backpressure gave more air to the primary burn. This resulted in an extremely clean burn as you can tell from this photo:
This has resulted in a very clean burn within the first 5 to 10 minutes of start up, which continues on as long as the boiler is running with a good bed of coals. Another great thing about this design has been the complete lack of sparks and ash escaping the stovepipe. I think the exhaust is some of the cleanest that I have produced.
In my next post, we’ll discuss my decision to insulate the outer body of the stove and lower pipe to further increase efficiency as well as delve into some of the calculations that brought me there. In my next video, I plan to show me building a fire and demonstrating how quickly it burns clean.
I wasn’t able to get any footage of installing the exhaust to water heat exchanger, but I did manage to take a picture of what the first two stages look like inside of some uninsulated stovepipe. Note how the stages offset:
The offsets make the exhaust snake through the stovepipe, further aiding in efficient heat transfer. This video shows how I insulated the stovepipe as well as how the plumbing system will work:
I have test fired it to be sure the downdraft works. The first run was very successful in spite of having fairly wet, punky wood. It did take about 30 minutes before it ran smokeless, but I’m hoping that adding a tiny bit more of primary air and having better fuel will shorten that time dramatically.
Once it reached operating temperature, the exhaust ran clear and odorless. I recorded a maximum of almost 80k BTU of actual heat being transferred to the water. When I have good wood to work with, I’ll be able to calculate how many BTU of wood is being burned and get a good idea of overall efficiency.
On a huge positive note, at that peak BTU production, I only measured the exhaust to be 145*F, meaning I’m pulling the vast majority of the heat out of the exhaust. I do wonder if having potentially condensing exhaust could become a problem. Time will tell.
Not much is left to do on this project. I need to install a rope gasket on the door, build a shed around the stove, and insulate it with mineral wool for maximum efficiency.
Tomorrow, I’ll release a video showing how I purge the air out of the plumbing system.
In my previous video, I had a bit of a disaster that really got me behind. Instead of building a small fire to cure the rigidizer, I’d recommend using a small amount of coals, a heat gun, or a propane torch. I ended up using a propane torch. Here’s the disaster aftermath:
This week, I’ve got the firebox completed, including fixing the damage to the top and insulating the door. Here’s my latest video that shows the repair (including extra insulation at the top of the boiler), illustrates how well my homemade rigidizer works, and how I’m beginning the hot gas to water heat exchanger:
As I mentioned in the video, in the interest of saving time, I’m using high temperature silicone adhesive instead of welding the pipes. I’ve tested it under several heating/rapid cooling conditions under direct flame, and it performs flawlessly. It also will give me the option of changing it in the future if I want to add more pipe. Here’s a view of my progress on the exchanger, I’ll have to buy a couple more pieces to complete it:
In order to seal in the dangerous fibers of the ceramic blanket and to add a hard wearing surface, I coated the blanket with a homemade rigidizer. It is made with roughly equal parts in volume of furnace cement and aluminum oxide:
I then add just enough sodium silicate to give it a smooth paste like consistency:
To apply it, I simply used a dollar store paint brush. Apply a thin coat and let it dry a couple hours between coats. Four coats seems to make a good rigid surface.
To cure it, a small fire will need to be built. It is important to slowly bring the temperature up to prevent bubbles from forming. When it is cured, it forms a hard wearing, durable surface.
I’ve been able to make a good deal of progress this week on the boiler. Next week, I should be able to build a small fire to cure everything. Then it’ll be off to the plumbing side of things. Here’s a video documenting my progress and revealing a quick peek at the hot gas to water exchanger:
Since making that video, I’ve gotten the top part of the grate constructed. It still needs the support structure to keep it from bending under heat.
Note all the holes. This is the same kind of material I used on my concrete block rocket stove and it works great.
As you can tell from the above photo, the easiest way for the gases to make it to the secondary combustion chamber is to travel down through the grate and out the rear. Using the manifold I showed in the video, most of the air will be directed under the grate to encourage good secondary combustion and to superheat the tiny coals that drop through. This will create a burn that produces very little ash. The ash that is produced is light and fluffy and is easily scraped out between loadings.
Hopefully the weather will hold next week. On my list of things to get accomplished is to finish the support system for the grate, install the secondary air injectors, finish the air inlet manifold, and insulating the door.
Learning from my mistakes in my initial build, as well as wanting to try new ideas, I’ve torn down the wood boiler and began to modify it. I also am using higher end materials instead of homemade concoctions. Here’s my progress so far:
Now I will have double the firebox space. To control combustion, I’m making a partition in the rear of the stove where secondary combustion will take place. The entry to this partition will be low and fairly small. This should also help increase burn time and prevent runaway combustion. Here’s a picture showing the partition construction from the primary burn chamber:
I’ll fill in the gaps with ceramic fiber insulation and coat the whole face with furnace cement. I still haven’t figured out exactly how I’m going to inject secondary air, but I have a few ideas. The firebrick will heat up and help maintain the temperatures necessary for secondary combustion to occur.
Here’s a view of the actual chamber itself:
Note how it has a small entry, but then rapidly opens up into a fairly decent sized chamber. I’m hoping that this will promote turbulence and encourage mixing with secondary air for a more complete combustion before it goes into the stovepipe.
Before I do the final installation of the partition, the ceramic fiber blanket will get a rigidizer applied to seal in the fibers and provide a hard wearing surface.
Next week, I’ll show how I plan to insulate the stovepipe and add my hot gas to water heat exchanger inside.