brick kiln, furnace, coal mine pit
窰 centers on an enclosed space for intense heat: a brick kiln, a furnace, or a coal mine pit where fire and earth meet.
窰 combines 穴 (hole, cavity) with 䍃, which likely contributes the sound and relates to earthenware or a pit. The character represents a kiln or furnace as a cavity in the ground.
The top 穴 is a cave or hole, and the bottom 䍃 looks like a container with fire inside. Picture a cave-like brick kiln where flames heat the earth.
For ヨウ, imagine a glowing kiln that looks like a bright yellow sun: yellow -> ヨウ, and the kiln radiates heat.