暖 is a meaning-and-sound character. 日, “sun,” points toward warmth, while 爰 mainly supplies the historical sound. Related older forms for “warm” were also written with 火, “fire,” so the written family did not always use exactly the same meaning component. This seal-form-inspired sketch keeps a clear sun on the left and an open, flowing 爰 on the right; it is a guide to the components rather than a claimed oracle-bone picture.
A piece of culture
Warmth you can feel and share 暖 can describe warm weather, a warm room or the feeling of being cared for. 暖心 literally joins “warm” and “heart” for something heart-warming. 温暖 / 溫暖 is the common word “warm” or “warmth”: useful for temperature, but also for the welcoming feeling of tea, food and people gathered together.