This Natural Draft Furnace Gets Hot Enough to Smelt Iron

This natural draft furnace can reach temperatures of 1200 Deg C with no mechanical assistance.
Jessica Miley

If you start to watch this video without reading the description, you could be thinking that Primitive Technology host was making an old-school pizza oven. But stay with the video and you’ll see something that would turn your margherita into dust before you can say ‘mamma mia’.

What the Primitive Technology channel is actually doing in this video is testing out some theories on how to make a natural draft furnace. The aim is to try and get a heat source going that relies on a strong draft to increase the temperatures in the furnace to be able to complete some basic metal smelting. The high chimney is so efficient at creating a draft that bellows of any kind aren’t required.

The YouTuber explains on his blog that he designed the furnace based on information from the book “The Mastery and Uses of Fire in Antiquity” by J.E. Rehder. The furnace is constructed from mud and creates airspeed within the furnace of 6 m per minute which is technically enough for iron smelting. Using the observation of the incandescence of the burning materials, the Primitive Technology host estimates the internal temperature of the furnace was about 120 degrees Celsius. Definitely hot enough to smelt iron. The furnace is designed to be fuelled by charcoal, but for ease of accessibility, in this instance, it was filled with wood and some charcoal, before being lit from the top. Wood was gradually added to the furnace along with a few handfuls of roasted bog ore. After allowing the fire to burn for more than an hour, it was left to burn away.