It was discovered during excavation that the Apsidal Hall was heated by built conduits beneath its floor. Specifically, beneath the floor of the apse two pipes were found; the first followed the perimeter of the foundations of the hall’s masonry, while the second, which ran N-S, passed through about the center of the apse. The two conduits intersected in the north part of the apse.
The peripheral duct had a width of 0.035 meters and a height of 0.070 meters. One of its sidewalls was brick, while the other was formed by the inner face of the apse foundation, which was built of rubble. The lower part of the conduit, as was determined by excavation, was covered by a combustion layer of burnt wood. The central conduit had a width of 0.44 meters and a height of 0.070 meters; its sidewalls were brick, while its floor was built of coarse-grained mortar. The cover slabs of the conduits were bricks measuring 0.51 x 0.76 x 0.06 meters.
The furnace (praefurnium), in which wood charcoal was burned to produce warm air, was at about the center of the apse wall. It had a vaulted opening (stomion) (width 0.060 m.) with brick sidewalls.
Smoke was carried off through vertical ceramic conduits enclosed in two recesses built into the thickness of the walls. One was on the southwest wall of the apse, and the other on the west wall at the north end of hall B.
