6″ Dragon Burner masonry heater using chimney flues – Part 1

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.

6" Rocket Heater Built with Flue Pipe - Barreless Rocket Heater

6″ Rocket Heater Built with Flue Pipe and Dragon Burner – (click to enlarge)

Specs

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.

Rocket Heater Burn Tunnel inside Flue Pipe

Top View of Burn Tunnel in flue pipe

Rocket Heater shippable core inside chimney flue pipe

Complete Dragon Burner – Ready for insulation (click to enlarge)

rocket heater shippable core with insulation and ash plate

Insulation installed and ash top plate in position (click to enlarge)

Rocket heater masonry bell build joint view

Joint between 1st and 2nd bell, just above ash plate (click to enlarge)

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.

Charts

Here is a chart of the 1st bell.

Rocket Heater temperature profile for 1st test bell

Temperatures for 1st Bell for 1st part of test (click to enlarge)

Here is a chart of the 2nd bell

Masonry heater with j-tube, temperature readings

Temperatures for 2nd Bell (click to enlarge)

Here is the combined chart

Masonry heater built with dragon burner j-tube temperature readings

Both 1st and 2nd bell temperature readings combined (click to enlarge)

Testo Graph

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.

Testo 330 analyzer chart of 6" dragon burner with masonry bells from chimney flues

Testo 330 gas analyzer chart of “a lot” of the burn (click to enlarge)

As you see the stack exit temperature stayed pretty much around the 200F target until the end of the fire when they climbed.

 

 

 

 

 

Click here for Part 2 

 

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Comments

  1. oboblomov says:

    Hi Sandy! This is very encouraging, as is the thread (http://donkey32.proboards.com/thread/829), which I refrain from posting to until I have something more substantial than dreams to contribute. The flue bell system you have pioneered here gives me some ideas which might just pry me away from all my other “pressing activities :-) ” and get cracking on a prototype bell stove using the 4″ Dragon Burner obtained from you some months back.

    Peter’s suggestion (on donkey thread) to use 13″ within 17″ flue tiles, and to slit the tiles and add a ceramic fiber gasket seems the way to go, and especially suited to the 4″ DB. Also, cutting the tiles on opposing sides seem intuitively better to me. QUESTION: Where do you buy metal (presumably stainless) strap and strapping tool? I’m very deficient on the materials/tools end, but assume the slit tiles and gasket must be held together somehow.

    Another QUESTION regards the material you have used to form the top of the 1st bell. I assume the 2nd bell cap could be a concrete paver or the like, but the first one must withstand some serious heat.

    So many good ideas! Thanks obob

    • SMathieu says:

      You do not need strapping material. The gasket is a tight enough fit.
      The caps were made from 3000F refactory material. You could use soapstone or other stone suitable to the heat, but I would recommend atleast 2″ if not 3″ for the caps.

      Thanks for the support!

  2. Ernie Nalty says:

    Sandy , I really like this flue design….do you think that you will ever offer a Front loading stove , Instead of the Top load ?

  3. William Behrendt says:

    I am sorry is the fuel wood or some other material like pellets?.

    • The fuel is cord wood in small diameters. It has to be small enough to fit at least 6 pieces of wood at a time to keep the fire hot and fast. Burning pellets efficiently would require a different design.

  4. I enjoyed reading this stunning article! Many thanks for sharing! Will be waiting for the next entry to be published.

  5. Thanasis says:

    How do you see the idea of a cooking top on first bell? And what material and thickness to use?

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