🏛️ Roman Hypocaust: Floor Warm-Up and Flue-Gas Heat Balance (2D cross-section)

2D cross-section of a Roman hypocaust: a furnace sends hot gas between clay pillars under a stone floor and out through a flue. Set the furnace power, gas flow, floor area and slab thickness, and watch the supply and exit gas temperatures, the heat reaching the floor and how many hours the slab takes to warm up. Same gas-side equations as the 3D page, with four in-page numerical checks.