noun, plural cal·dar·i·a [kal-dair-ee-uh] /kælˈdɛər i ə/.
Examples from the Web for caldarium
See Note 16, p. 511, for discussion of yellow and caldarium copper.
The caldarium and the side of the tepidarium next to it were provided with hollow walls; a hollow floor extended under both rooms.
A doorway led from the tepidarium into the caldarium, or vapor-bath.Museum of Antiquity|L. W. Yaggy
Coming from these two sources the caldarium must have been, indeed, impure.
At one end of the caldarium we find the bath basin, alveus; at the other is the support of the labrum, which has disappeared.