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.
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.
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 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.
Spring is in full swing and grilling is one of my favorite outdoor pastimes. I had an old propane grill that needed a new burner assembly, but I decided instead of buying propane, why not grill with sticks from my yard?
If you have followed my blog for any length of time, you might recall my 13 block rocket stove. I decided to use this as the heart of my project. Here’s two videos that show how I got combined the rocket stove with the old propane grill and how I made the system better:
It only takes a couple of minutes to bring the grill up to temperature, so propane holds almost no advantage over wood. Nearly all the trees on my property are oak, so I have no shortage of hardwood to grill with.
A project I am currently working on is taking wood gas from the bottom of the heat riser. My plan is to use it to run the side burner with. I have successfully gotten wood gas from the inside of the stove, but not enough to sustain the burner. I’ll continue working on it. In the future, I plan to upload videos of the wood gas burner as well as some cooking videos that illustrate how well it works.
Forced air induction is a great feature to have on a wood burning device. It is like a supercharger, boosting the amount of oxygen available, increasing heat output. It also gives you greater control over the fire, which is great when you are trying to maintain a comfortable temperature indoors with a wood boiler. Here’s some details on how I added forced air induction to my DIY outdoor wood boiler:
It works by kicking the blower on and off based on the water temperature. Wood boilers are designed to run around 180*F. By setting the fan to kick off at 160*, natural induction allows it to slowly rise to the 180* mark, thus lowering BTU output and burning the wood slower. If you set the blower to kick off at 180*, BTU output is increased to 120,000 BTU per hour, taking the chill off the house rapidly, and consuming 22 pounds of wood an hour.
I have the furnace blower set to kick on at 165*. This compensates for the thermocouple having to read water temperature through the copper pipe, preventing boil overs. It turns off at 160*, allowing the water temperature to rise.
I’ve been experimenting with using an alarm to let me know when to add wood to the fire. So far, it has been a bit problematic. If I can work the bugs out, I’ll be sure to share that system.
As I mentioned in the build video, I was planning several modifications to make the stove more efficient and user friendly. Here is a video that shows what I have done so far to accomplish just that:
As you can tell, I’m bringing more heat indoors with a lot less being wasted out the flue. There are still many things I plan to do to make the stove even better and I’ll be sure to continue documenting the modifications I make.