Our redesign on the masonry heater using chimney flues included two major changes. As you may recall from the end of Part 1, we were thinking of lining the first bell with fire clay brick in order to store the heat and keep the flue liner from cracking. Peter van den Berg suggested that we put a smaller flue liner into the larger one instead. Each piece of the smaller flue liner was also split on one side to allow for thermal expansion without cracking. We cut the smaller flue liner vertically using a diamond blade in an angle grinder and then inserted a ceramic fiber gasket into the cut. No strapping was used to hold the piece together.
Although the firebrick approach would probably perform a bit better, it would be a great deal more time consuming and expensive to do. Our goal is to design a heater which delivers most of the performance of a full masonry heater, but can be built quickly and inexpensively. The performance data of this build are very good and are covered in part 3.
Like the first build, the tallest bell is 7’. The second bell is 6’. These two bells are 17” x 17” on the outside. The 13” x 17” flue containing the heat riser is 4’ 8” tall. The burn tunnel flue liner has been reused from the 1st build and is 14¼” tall.
Notice that the opening between the first and second bells is one foot tall here at the bottom of the heater. So, the gases go up the first bell to the top, cool and fall down, then do the same in the second bell before exiting to the chimney.
Below is the burn tunnel-heat riser stack. The 17″ long side of the heat riser flue lines up with the first bell. (The burn tunnel is off-center; it will be fixed later.) Premixed fireclay has been used to seal the openings between these two pieces of flue liner.
Heat Riser Exhaust
In the first bell, both the inside and outside flue liners are cut at the same level. We need plenty of space for the gasses to flow from the heat riser into the bell.
Fire clay Brick
So, now most of the main structure is done. The goal of the next steps was to keep the
the temperature of the flue liner outside of the heat riser cool enough that tile could be adhered to the outside for decoration. In order to do this, we lined it with fire clay brick. As you can see in this image, a small platform was temporarily constructed inside the heat riser flue. The bottom of the bricks has to be below the top of the vermiculite boards of the heat riser (when in place).