加熱
かねつ · kanetsu · JLPT N2 · noun
heating
🔥 加 (add) + 熱 (heat) = adding heat; 熱 is the hot character, 加 means to add or apply
加熱 breaks into 加 (add, apply) and 熱 (heat). Together they mean applying heat, as in cooking or warming something up.
加 — force 力 + mouth 口
加 is traditionally analyzed as a compound of 力 (strength) and 口 (mouth), suggesting boasting or exaggerating one's effort with words. From this it extended to the meaning 'to add' or 'increase'. Today it is used broadly for addition, both literal and figurative.