Derrick – 8″ Rocket Masonry Heater – Part 1 Description

8" Dragon Masonry Heater - Rocket Heater for Greenhouses, Shops and Barns

8″ Dragon Masonry Heater – The Derrick

The Derrick is designed for larger spaces where looks are not a criteria, such as greenhouses, barns, and shops. Like the Castle Build, all the heat is stored into thermal mass (firebricks). Exit temperatures did not exceed 170°F. Its main features are:

            • It can be easily assembled and disassembled
            • It uses steel drums and firebricks rather than chimney flue liners for construction
            • Less expensive materials than the Castle Build
            • The heaviest individual components are the steel drums
            • It has a small foot print
            • It stores 50K-60K BTUs per hour of burning
            • It radiates about 18K – 20K BTUs an hour
            • Maintains lower surface temperature at the height of people, than a rocket stove barrel.  Temperatures are more similar to radiators rather than cast iron stoves, for safer and more even heating


This build is similar to the Castle build, except there is only one bell or chamber. The two black barrels house the Dragon Heater Core; we refer to the stack as the “Heat Riser Tower”. The set of 2 red drums and 1 black is the “Bell Tower” where the heat is captured. The connecting passage between these two towers is called the “Exhaust Collar”.

The wood is loaded vertically into the 8″ rocket heater core (brown box) where it is burned horizontally through the burn tunnel and then up the heat riser. The exhaust is routed via the collar to the Bell Tower. Inside the bell, hot gases naturally rise and the cooler ones sink and exit the Bell Tower at the bottom via the chimney pipe.  Although the gases can be over 800° at the top of the bell tower, the chimney exit temperature did not exceed 170°F.

Heat Riser Tower (Black Drums)

Dragon Rocket Heater 8" Core in Hardiboard Container

Dragon Rocket Heater 8″ Core in Hardie Board Container

As in the Castle Build, the Derrick’s 8″ heat riser is insulated on all sides. The sides of the barrel are lined with ceramic fiber blanket for insulation. This way,  more of the heat goes into the Bell tower and is not lost through radiation.

Dragon Heater Derrick Heat riser top view

Exhaust Collar

You can see the collar at the top of the Heat Riser Tower provides a path for exhaust into the Bell Tower.

Dragon Heater Derick Collar Side View

Closeup of collar from the side

View from Heat Riser to Bell Tower before adding exhaust collar

View from Heat Riser to Bell Tower before adding exhaust collar






Dragon Heater Derick exhaust collar viewed from Bell Tower

Dragon Heater Derick exhaust collar viewed from Bell Tower

Rocket Heater Masonry Build using Firebricks

Top view of the inside of the Bell Tower


Bell Tower

The Bell Tower shown in the images with the 2 red drums and 1 black one, is filled with stacked firebrick. There are openings at the bottom for the chimney exhaust and on one side to connect to the Heat Riser Tower. Otherwise, the entire height of 3 barrels is filled with firebrick.

55 gallon Drum Barrel Cap for Rocket Heaters

55 gallon Drum Barrel Cap

Barrel Caps

At the top of each tower we have replaced the metal lids of the barrels with caps  made from 3,000°F heat-absorbing refractory. These refractory caps serve two purposes.

First, the caps store heat; when firing, they get to be over 600°.

Secondly, since the air temperature at the top of the heat riser tower can be ~1,200°F for extended periods, the caps will handle the heat better than steel during repeated firings.

Without these caps, the underside of the steel tops should be insulated with ceramic fiber  blanket, particularly in the heat riser tower.

Next post will be the data logs from our three hour test fire.


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