Reference for Shabbat 76:11

מעשה שעשו אנשי טבריא והביאו סילון של צונן לתוך אמה של חמין אמרו להם חכמים אם בשבת כחמין שהוחמו בשבת ואסורין ברחיצה ובשתיה אם ביום טוב כחמין שהוחמו ביום טוב ואסורין ברחיצה ומותרין בשתיה:

He answered: Its heat is greater than a [double] stove's but less than an oven's.<span class="x" onmousemove="('comment',' Hence it occupies an intermediate position. ');">¹⁶</span> What is a kuppah and what is a [double] stove [kirah]? — Said R. Jose b. Hanina: A kuppah has room for placing one pot; a [double] stove [kirah] has room for placing two pots. Abaye — others state, R. Jeremiah — said: We learnt likewise: If a [double] stove [kirah] is divided along its length, it is clean; along its breadth, it is unclean; [if] a kuppah [is divided], whether along its length or along its breadth, it is clean.<span class="x" onmousemove="('comment',' When the kirah is divided along its length it cannot be used at all, hence it ceases to be a utensil and is clean (cf p. 163, n. 9); but when divided along its breadth, each portion can be used for one pot, and it is therefore subject to uncleanness. Since a kuppah has room for only one pot, whichever way it is divided it ceases to be a utensil and is clean. ');">¹⁷</span>

Jastrow