6” Dragon Burner masonry heater using chimney flues - Part 2

Posted by Sandy Mathieu on 3rd Aug 2013

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.


Foundation for Rocket Heater Double Bell Masonry Build with Chimney Flues

Foundation for Bells, 1st Bell is to the right. opening on the left is for ash clean out, the opening at the bottom is for a 12″ x 4″ to 6″ chimney adapter
(Click to Enlarge)

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.

Rocket Heater Masonry Build using Chimney Flue Pipe - Inner Flue

This shows the liner put into the 1st bell. (click to enlarge)

The 2nd bell does not need a liner. Bottom right square. (Click to enlarge)

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.


Double wall flue liner bell for rocket heater made with dragon burner

Here you can see the ceramic fiber in the side of the inside flue liner.

 Rocket Heater Heat riser opening on Dragon Heater Masonry Build

This shows the top piece of the heat riser section, where the exhaust will enter the 1st bell. Notice the liner flues in the 1st bell. (click to enlarge)
(click to enlarge)

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.

The inside flue liner has fireclay on it and is ready for the next layer.

Notice the next layer has a slit with ceramic fiber in it on the opposite side and a huge cut to let the gases into the second bell.

Inside the bell on the left is another piece of 13” x 13” x 2’ flue liner with a slit and ceramic fiber tape. The 17” x 17” x 1’ pieces on the outside are not cut.

Inside the bell on the left is another piece of 13” x 13” x 2’ flue liner with a slit and ceramic fiber tape. The 17” x 17” x 1’ pieces on the outside are not cut.

Fireclay 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).

These 2×4 studs support the OSB on which the fireclay bricks rest.

Several more bricks have been added to the inside of the flue liner. The ones at the top of the image handle the transition to the first bell.

The leaning board is supporting the fireclay bricks which are lining the opening to the first bell.

The heat riser is shown in this image. As you can see with the fireclay brick on all sides, it’s a tight fit.

Now the temporary scaffolding is gone and the perlite has been added for more insulation around the heat riser. The white string is actually a thermocouple.