热 (traditional 熱) sits on 灬 — the 'fire' radical, four dots that represent flames at the bottom of a character. Fire underneath = HEAT. You met the same 灬 in 点; here it's literal warmth.
热 is hot — weather (今天很热, today is hot), water (热水, hot water — vital, since Chinese traditionally drink hot water, 喝热水, for health), food. Figuratively it's warmth and enthusiasm: 热心 (warm-hearted, kind), 热闹 (lively, bustling — 'hot-noisy', a very positive word for a fun, crowded scene), and 火热 / 很热 for something wildly popular. Chinese culture prizes 热闹 — a quiet party is a failed one.
Flames (灬) at the bottom — HOT.
热闹 ('hot-noisy') is a compliment — it means lively and bustling, the ideal atmosphere for a gathering. And Chinese drink 热水 (hot water) for health, even in summer.