These kilns derive their name from the fact that the heat is continuous and the kilns are kept continuously burning. Continuous kilns are very different, both in construction and working, from the other two styles, and are also very expensive to construct. There are various styles of continuous kilns, each being protected by letters patent.
The most common type is that of two parallel brick tunnels connected at the ends. The outer walls are sometimes 8 feet thick at the bottom and 4 feet thick at the top. Various flues are built in these walls. The coal in continuous kilns is put in from the top. The bricks are piled in the kilns in sections, the sections being separated by paper partitions, and each section is provided with about four openings in the top for putting in the coal. After the kiln is started one section at a time is kept burning, and the heated gases are drawn through the next section so as to dry the bricks in that section before burning. There are often twenty or more sections in one kiln, and while one section is being burnt and others dried, others are being filled and others are cooling or being emptied.
Continuous kilns require a powerful draft to make them work successfully; this draft is generally provided by a tall stack.
The principal advantages claimed for the continuous kiln are that it takes less fuel to burn the bricks, and a greater percentage of No. 1 bricks are obtained than in other kilns. The question of the kind of kiln to be used, however, is principally one of economy to the manufacturer, as it makes no particular difference to the architect in what kind of a kiln the brick are burnt.