Reference for Kelim 5:6
תַּנּוּר שֶׁנָּתַן בּוֹ עָפָר עַד חֶצְיוֹ, מֵעָפָר וּלְמַטָּן, מִטַּמֵּא בְמַגָּע. מֵעָפָר וּלְמַעְלָן, מִטַּמֵּא בַאֲוִיר. נְתָנוֹ עַל פִּי הַבּוֹר אוֹ עַל פִּי הַדּוּת, וְנָתַן שָׁם אֶבֶן, רַבִּי יְהוּדָה אוֹמֵר, אִם מַסִּיק מִלְּמַטָּן, וְהוּא נִסּוֹק מִלְמַעְלָן, טָמֵא. וַחֲכָמִים אוֹמְרִים, הוֹאִיל וְהֻסַּק מִכָּל מָקוֹם, טָמֵא:
An oven half filled with earth - the part from the earth downwards contracts impurity by contact; the part from the earth upwards contracts impurity [also] from its air-space. If the oven is placed over the mouth of a cistern or over that of a cellar and a stone is placed at its side: Rabbi Yehudah says: if when heated from below it becomes also heated above it is susceptible to impurity. But the Sages say: since it was heated in any case it is susceptible to impurity.