At the KM2 and KM3 sites, Schmidt tested the hypothesis that the high combustion temperature of furnaces, discovered to be between 1,350–1,400 °C (2,460–2,550 °F), was caused by the preheating of air blasts.

Preheating has been suggested to be a distinct feature of African Early Iron Age smelting techniques by ethnographic observations of the Haya people of northwestern Tanzania.

It was discovered during a village survey by a Tanzanian surveyor, who observed furnace bricks on a main path bisecting the site.

[5] In KM2, large amounts of industrial debris and domestic pottery were dumped into a refuse pit alongside discarded furnace bricks, slag, tuyères, iron fragments, and charcoal.

[3] Preheating of air blasts allowed the furnaces to achieve higher combustion temperatures, which dramatically improved fuel efficiency in the iron production process.

Peter Schmidt observed that the Haya in northwestern Tanzania employed the practice of preheating by placing tuyères inside their furnaces, which results in hot air blast.

[2] The study of KM2 and KM3 sites allowed for the collection of more definitive evidence for prehistoric tuyères, in order to discern how and when preheated iron technology developed in Africa.

The majority of tuyère fragments show convincing evidence in their colors to indicate that they were inside the prehistoric smelting furnaces of KM2.

[3] The hypothesis that preheating had developed at least by the 400 AD in Africa has been confirmed by the discovery of a 36 cm (14 in) whole or long section of tuyère uncovered in furnace 9 of KM3.

[4] Ethnographic evidence suggests that iron smelters excavated holes in their furnaces in order to place in it magical devices or ritual medicine.