kitchen range, cooking stove
灶 centers on a heat source for cooking: a kitchen range or cooking stove, where fire meets a solid base.
灶 combines 火 (fire) and 土 (earth), suggesting a cooking stove made of earth or clay where fire is built.
Fire 火 on the left and earth 土 on the right: picture a traditional earthen stove with a fire burning inside, used as a kitchen range.
For ソウ, imagine the soul of the kitchen—the stove—warming the house: soul -> ソウ, and the fire on the earthen stove is its heart.