This was a three and one quarter hour firing, with the object of raising the temperature of the furnace as quickly and as high as possible. We removed the pots and shelves to allow a decent draw and airflow, and started with a residual furnace temperature of 119°C.

We started with a mix of Chestnut and Sycamore for the first one and a half hours, burning 30kg at an average rate of 20kg/hr, then switching to Opepe (with its higher calorific value), burning 45kg at an average rate of 25.71kg/hr.

The rate of climb was as expected: starting fast and slowing as the temperature was raised (see graph).

It was important to keep the tunnel under the grate free of ash to allow plenty of airflow. At around 1270°C we tried to increase the burn by opening the ash hole and throwing wood into the firing chamber, but to no noticeable effect. Perhaps the intake of cold air was offsetting the heating effect of the extra wood.

We achieved a top temperature of 1283°C, and no amount of coaxing could raise the temperature any higher. Even so, this was better than the 1250°C we reached in the Pot Furnace in 2005.