ὑπό-καυσις · hypo-kausis — LSJ
burning underneath, Dieuch. ap. Orib. 4.5.2.
burning of bricks, ὑ. τῆς ὀπτῆς (sc. πλίνθου) POxy. 2153.12 (iii A. D.).
the fire of the hypocaust, Vitr. 5.10.1, Plu. QConv. 2.658e; heating by this means, IGRom. 4.1210 (Thyatira); βαλανείου POxy. 2127.8 (ii A. D.).