A baking oven originally must be no less than four handbreadths [high] and what is left of it four handbreadths, the words of Rabbi Meir. But the sages say: this applies only to a large oven but in the case of a small one it originally can be [any height] and what is left is the greater part of it. [Its susceptibility to impurity begins] as soon as its manufacture is completed. What is regarded as the completion of its manufacture? When it is heated to a degree that suffices for the baking of spongy cakes. Rabbi Judah says: when a new oven has been heated to a degree that sufficed for the baking of spongy cakes in an old one.

A double stove: its original height must be no less than three fingerbreadths and what is left of it three fingerbreadths. [Its susceptibility to impurity begins] as soon as its manufacture is completed. What is regarded as the completion of its manufacture? When it is heated to a degree that suffices for the cooking of the lightest of eggs when scrambled and put in a saucepan. A single stove: if it was made for baking its prescribed size is the same as that for a baking-oven, and if it was made for cooking its prescribed size is the same as that for a double stove. A stone that projects one handbreadth from a baking-oven or three fingerbreadths from a double stove is considered a connection. One that projects from a single stove, if it was made for baking, the prescribed size is the same as that for a baking-oven, and if it was made for cooking the prescribed size is the same as that for a double stove. Rabbi Judah said: they spoke of a ‘handbreadth’ only where the projection was between the oven and a wall. If two ovens were adjacent to one another, they allot one handbreadth to this one and one to the other and the remainder is clean.

The crown of a double stove is clean. The fender around an oven: if it is four handbreadths high it contracts impurity by contact and through its air-space, but if it was lower it is clean. If it was joined to it, even if only by three stones, it is unclean. The place [on the stove] for the oil cruse, the spice-pot, and the lamp contract impurity by contact but not through their air-space, the words of Rabbi Meir. Rabbi Ishmael rules that they are clean.

An oven that was heated from its outside, or one that was heated without the owner's knowledge, or one that was heated while still in the craftsman's house is susceptible to impurity. It once happened that a fire broke out among the ovens of Kefar Signah, and when the case was brought up at Yavneh Rabban Gamaliel ruled that they were unclean.

The additional piece of a householder's oven is clean, but that of bakers is unclean because he rests the roasting spit on it. Rabbi Yohanan Hasandlar said: because one bakes on it when pressed [for space]. Similarly the additional part of the boiler used by olive cookers is susceptible to impurity, but that of one used by dyers is not susceptible.

If an oven was half filled with earth, the part from the earth downwards contracts impurity by contact only while the part from the earth upwards contracts impurity [also] from its air- space. If he put the oven over the mouth of a cistern or over that of a cellar and he put a stone at its side: Rabbi Judah says: if when heated below it becomes also heated above it is susceptible to impurity. But the sages say: since it was heated, no matter how, it is susceptible to impurity.

If an oven contracted impurity how is it to be cleansed? He must divide into three parts and scrape off the plastering so that [the oven] touches the ground. Rabbi Meir says: he does not need to scrape off the plastering nor is it necessary for [the oven] to touch the ground. Rather he reduces it within to a height of less than four handbreadths. Rabbi Shimon says: he must move it [from its position]. If it was divided into two parts, one large and the other small, the larger remains unclean and the smaller becomes clean. If it was divided into three parts one of which was as big as the other two together, the big one remains unclean and the two small ones become clean.

If an oven was cut up by its width into rings that are each less than four handbreadths in height, it is clean. If he subsequently plastered it over with clay, it becomes susceptible to impurity when it is heated to a degree that suffices for the baking of spongy cakes. If he distanced the plastering, and sand or gravel was put between it and the oven sides of such an oven it has been said, "A menstruant as well as a clean woman may bake in it and it remains clean."

An oven which came cut up in sections from the craftsman's house and he made for it hoops and put them on it, it is clean. If it contracts impurity, and then he removed its hoops it is clean. If he put them back on, it is still clean. If he plastered it with clay, it becomes susceptible to impurity and there is no need to heat it since it was once heated.

If he cut the oven up into rings, and then he put sand between each pair of rings, Rabbi Eliezer says: it is clean. But the sages say: it is unclean. This is the oven of Akhnai. As regards Arabian vats, which are holes dug in the ground and plastered with clay, if the plastering can stand of itself it is susceptible to impurity; Otherwise it is not susceptible. This is the oven of Ben Dinai.