We were looking for a simple way to build a bell style masonry heater. This build does not use a barrel that is commonly used in rocket heater designs with J-tube style combustion chambers. We decided to try using commonly available chimney flue pipe sizes to construct a quick and dirty masonry heater using a dragon burner as the combustion chamber.
This approach we knew would be sub-optimal due to the materials in clay flue pipe, but decided to give it a try without lining it with firebrick, just to see how it did. Below is a picture of the mostly assembled heater.
Although we will re-configure it for the 2nd round, we were overall impressed by its strong drafting through out the burn, its ability to extract most of the heat, and its dead simple build. Our target exit temperature of around 200F (to avoid condensation problems) was maintained pretty well.
The left column is 7 ft tall and the right 5. Each column is a bell, the larger bell is where the heat riser is and the is the 1st bell. Each block is a 17×17 flue pipe. The feed tube is in a 13×13 flue pipe cut down to size. Below are some pictures of the construction.
We fired the unit for 4 hours to see what kind of heat build up we would get, if the draft deteriorated and what the external temps of the pipe would be after long firing.
About an hour into the burn there were some very loud pops. Which made us more than a little nervous. After a moment we could see that the top 3 pipes had cracked. The fissure stayed pretty much the same through the rest of the burn. According to the manufacture, this is typical. Evidently 90% of the chimneys have cracks, just no one sees them since they are covered.
There are 2 ways to not have this, one is to only heat the pipes at 50 degrees an hour, or two, line the chambers with fire clay bricks. We had intended to do this anyway after the plain test, so that will be our next test. The fire clay bricks should help the unit absorb more heat quicker, so it will be interesting to compare numbers with the next build.
Here is a chart of the 1st bell.
Here is a chart of the 2nd bell
Here is the combined chart
The draft number which are recorded, but do not show up in the graph went from .004 at start to a high of .213 in H2o. Most of the run was over .1.
I think there was a problem with the pump in the testo so I took it out, as you can see. As the fire is dying the numbers are not as good, as expected. I am still learning the equipment and hope to have even better charts in the future.
As you see the stack exit temperature stayed pretty much around the 200F target until the end of the fire when they climbed.