Primitive Technology – Building A Primitive Natural Draft Furnace

SHARE

Advertisement

I built a natural draft furnace to test ideas about how hot a furnace could get without the use of bellows. Natural draft is the flow of air through a furnace due to rising hot air. The hot gasses in the fuel bed are more buoyant than the cold air outside the furnace causing them to rise.

image/text credit: Primitive Technology 

Fresh combustion air then enters the base of the furnace to replace the rising combustion gasses, keeping the fuel bed burning. These types of furnaces were once used for smelting copper and iron ores in around the world in ancient times, usually using charcoal as a fuel and in some cases wood too.

image/text credit: Primitive Technology 

The furnace was filled with wood and lit from the top. The fire burnt down the furnace producing charcoal. On reaching the tuyere the fire then started burning the charcoal. Wood was also continually added from the top along with a few small handfuls of the roasted bog ore (not shown in the video).

Advertisement

The temperature of hot objects can be visually estimated from their incandescence. After about an hour, the light coming out of the tuyere was high yellow to white hot indicating a temperature of at about 1200 c.

This experiment shows that high temperatures can be achieved without the use of bellows or charcoal, which might significantly reduce labour in the production of iron.The furnace was technically easy to build as it was a simple vertical cylinder. When running, the wood added to the top of the furnace converts to charcoal in the upper part of the stack and is consumed in the lower part. The ore I used was new to me, normally I use iron bacteria as an ore.

VIAPrimitive Technology
SHARE