Derrick – 8″ Rocket Masonry Heater – Part 2 Data Log 3 Hour Burn

Here is a short video of the construction with pictures of the data logging equipment hookup.


This stove worked well and considering its output and inexpensive construction it definitely has a place. Overall efficiency was an even 90 Percent, with average CO emissions of 778 ppm. These numbers would beat almost all the commercial stoves on the market. The maximum stack temperature was 175F, which means it is doing an excellent job of heat extraction. 6 hours after the last wood was added the surface temps at the top were still over 130 and bricks over 220. The heater was sitting outside, so convection losses were probably higher than those inside a building.

This is design offers complete heat capture of a highly efficient combustion system in a small foot print which can be easily assembled and disassembled and is inexpensive.

Exit Temperatures from Masonry Rocket Heater

Exit Temperature

Exit Temperatures

As you can see it took well over an hour to reach target exit temperature of over 140F.  For the 1st hour the temps are very low. So be careful about your chimney. Low exit temperatures with a large thin walled chimney located outside, could result in stove stalling. We ran this with an 18ft insulated chimney.

8" Derrick Rocket Heater Efficiency and Emmssions

Efficiency & Emissions


Efficiency and Emissions

As you can notice the efficiency at the beginning of the burn do not seem correct. I believe this is the by product of ballast gases being flushed 1st, while the ombustion gases collect at the top of the bell. It is not until the burn is well underway that these equal out. But as you can see it burns at a very nice even high efficiency.

The spikes in the co correspond to wood loads. As the fire burns down the CO number increase until a new load of wood is applied. The emissions levels also are generally lower as the system heats up. Other than the fuel loading spikes, you can see the back end of the burn is much lower than the 1st.

Heat Capture -Temperature Logs

One of the factors that makes this such and effective design is that firebricks store heat 7 times faster and retain twice as much heat as clay flues or cob. This means we need only half as much mass and fewer hours burning to store the heat as with a cob or clay flue based approach. The logs are shown in 2 parts because the computer locked up midway.

Dragon Rocket Heater Tower Temps Air Temperatures

The most surprising number on this chart was how hot the top of the Heat Riser Tower became. The sensor was over 20 inches from the top of the heat riser. It takes about 30 min. for the temperatures to really start rising.

8" Dragon Heater Derrick Thermal Mass Log

Brick Temperatures

The thermal stratification in the system can be easily seen in the Brick temperatures. These bricks can be heated up to 2000F so they can absorb a lot of heat. As you can see the temperature increase was fairly constant at 100Degrees/hour for the middle bricks and 200 degrees/hr for the upper bricks.

8" Derrick Rocket Heater Data LogSurface

The radiating surface area of this stove is way over 80 sq. ft. The temperatures are in the range of radiators, except for the very high locations, such as the barrel caps and top barrel. The red line is about 4 ft high. These low surface temperature makes for a safer stove. The large radiating surface are provide a lot heat evenly radiated.

Dragon Heaters 8" Derrick Heat Loss 1

8" Rocket Heater Heat Loss hours 4-6

Heat Loss Temperature Log

Our design goal for this stove was to be able to radiate heat for 2x as long as the stove was burned. So we monitored heat loss for 6 hours after burning. The charts are in 2 parts because the computer locked up in this second series. So there is about 2 hours of data missing in the middle.

Notice how much quicker the heat is lost from the cap (the purple line), versus the bricks. This is probably due to the fact that the system was outside and the caps would be exposed to more wind and air movement, and thus convective heat losses. Also notice the nice even surface temperature from the barrel.

After 6 hours the system has lost a lot of heat but the top barrel is still at radiator temperatures of over 130F.


© Dragon Heaters 2013, All rights reserved.



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