heat
烔 centers on heat, specifically the heat produced by fire.
烔 combines 火 (fire) with 同, which likely contributes the sound. The exact historical development is uncertain, but the modern form clearly links fire to heat.
Fire 火 on the left and 同 on the right: picture a fire that makes everything the same temperature—hot. 烔 means heat.
For トウ, imagine touching a hot stove: the 'tow' sound of touching something hot cues トウ, and the fire 火 on the left reinforces the heat.