A "Hoffmann kiln", "ring oven" or "ring kiln" was a massive oven in which clay was baked at a temperature of around 1,000° Celsius (1830°F) to produce bricks and tiles. It was a circular, elliptical or rectangular brickwork structure that consisted of an endless tunnel, divided into 12 to 24 chambers, all interconnected to each other and to a main flue

The Hoffmann kiln is a so-called "continuous kiln" - it burns 24 hours a day, 7 days a week, 365 days a year (except when it goes down for maintenance). Before its invention, bricks and tiles were fired in so-called "periodic kilns"