Left fire radical - pictograph of leaping flames. The indexing radical, marking
烘 as a fire/heat verb: to bake, dry by warmth, or roast gently. Same radical groups
烘 with
烧 (burn),
烤 (roast),
烫 (scald). Gentle drying heat - like an oven on low - is the precise nuance, distinguishing
烘 from violent burning.