暖かい and 温かい: warm surroundings, objects, and feelings
Both words are read あたたかい. Learn their common associations with climate and surroundings or with food, touch, and kindness, without treating the spellings as completely separate in every context.
暖かい: climate and surrounding warmth
暖かい is frequent with weather, seasons, and rooms that feel comfortably warm. 今日は風がなくて暖かいです。 and この部屋は日当たりがよくて暖かいです。 describe warmth in the air and the surrounding space.
It can also describe an item that creates a warm environment around the body. 暖かい毛布に包まれて眠りました。 emphasizes the comfort provided by a warm blanket. A rule that every physical object must take 温かい would therefore be too strict.
温かい: food, touch, and human warmth
温かい is common for food and drink at a pleasantly warm temperature. 寒い朝に温かいお茶を飲みました。 and 温かいスープを用意しました。 focus on the temperature of something consumed.
It is also widely used for kindness in 温かい言葉 and 温かい心. 皆が温かい言葉で励ましてくれました。 describes caring words rather than measurable heat.
Overlap and hiragana spelling
The spellings can overlap according to context and editorial style. Hands, clothing, and sunlight can be viewed either as individual sources of warmth or as part of a surrounding atmosphere, so writers may choose different emphases.
Everyday writing may use あたたかい in hiragana without showing the distinction. Use 暖かい部屋 and 温かいお茶 as helpful representative combinations, but do not declare every other spelling wrong without context.
Quick check: What kinds of warmth does 温かい express in 温かいスープ and 温かい言葉?
Show the answer and why
The first refers to the pleasant temperature of soup, while the second refers to kind and caring words. Both are representative uses of 温かい.