כירה שהיא עשויה כקדירה ושופתין על פיה קדירה למעלה ויש בה מקום שפיתת שתי קדירות אם הוסקה בגפת שהיא פסולת של זתים או בעצים אסור ליתן עליה תבשיל מבע"י להשהותו עליה אלא א"כ נתבשל כל צרכו והוא מצטמק (פי' הולך וחסר) ורע לו דליכא למיחש שמא יחתה או שהוא חי שלא נתבשל כלל דכיון שהוא חי מסיח דעתו ממנו עד למחר ובכל הלילה יכול להתבשל בלא חיתוי אבל אם נתבשל קצת ולא נתבשל כל צרכו ואפי' נתבשל כל צרכו והוא מצטמק ויפה לו חיישינן שמא יחתה ואסור להשהותו עליה אא"כ גרף דהיינו שהוציא ממנה כל הגחלים או קטם דהיינו שכסה הגחלים באפר למעט חומם ואם נתן בה חתיכה חיה מותר כאלו היתה כולה חיה דע"י כך מסיח דעתו ממנה ואפי' אינה גרופ' (פי' שמשך הגחלים מהתנור) וקטומה [פי' שכסה הגחלים באפר] מותר לסמוך לה קדירה בסמוך חוצה לה ואם הוסקה בקש או בגבבא מותר לשהות עליה אפי' אינה לא גרופה ולא קטומה: הגה שני כירות המתאימות זו אצל זו ודופן של חרס ביניהם האחת גרופה וקטומה והשני' אינה גרופה וקטומה מותר לשהות על הגרופה וקטומ' אע"פ שמוסיף הבל משאינה גרופה וקטומה (גמ' פ' כירה) ותנור אפי' אם הוסק בקש או גבבא אסור אפילו לסמוך לו אפילו אם גרוף וקטום: הגה כ"ז שהיד סולדת בו [הגהות מרדכי] וכ"ש שאסו' לשהות בתוכו או על גבו וכופח שהו' מקו' שפיתת קדיר' אחת אם הוסק בקש או גבבא דינו ככירה בגפת או בעצים דינו כתנור [והתנורים שלנו דינם ככירה] [ר"ן ר"פ כירה וכל בו וכן משמע מפירש"י] ואם שכח ושהה אם הוא תבשיל שבשל כל צרכו מותר אפי' הוא מצטמק ויפה לו ואם הוא תבשיל שהתחיל להתבשל ולא בישל כל צרכו אסור עד מוצאי שבת ואם עבר ושיהה אסור בשניהם: הגה עד בכדי שיעשו (הגהות אשירי ורמב"ם פ"ג) ואם החזירם עכו"ם בשבת דינו כשכח ושיהה [הגהות אשירי] ואם החזירם ישראל דינו כעבר ושיהה [הגהות מרדכי] ואם מצטמק ורע לו מותר שהרי לא נהנה מן האיסור [ב"י וע"ל ריש סי' רכ"ז] וי"א שכל שנתבשל כמאכל בן דרוסאי (פי' שם אדם שהי' אוכל מאכלו שלא נתבשל כל צרכו) או שנתבשל כל צרכו ומצטמק ויפה לו מות' להשהותו על גבי כירה: הגה או אפי' על גבי תנור (המגיד פ"ג והגהות מרדכי ומיי' פ"ג וריש פ' כירה ב"י) אפי' הוסק בגפת ועצים ואפי' אינה גרופה וקטומה ולא הוזכרה גרופה וקטומה והיסק בקש ובגבבא אלא כשהתחיל להתבשל ולא הגיע למאכל בן דרוסאי וכן לענין אם נטל הקדירה מעליה ובא להחזירה עליה בשבת ואם שכח ושיהה תבשיל שהתחיל להתבשל ולא הגיע למאכל בן דרוסאי אסור ואין צריך לומר אם עבר ושיהה: הגה ונהגו להקל כסברא האחרונה. וכל זה בענין שהיה שהקדירה יושבת על כסא של ברזל או על גבי אבנים ואינה נוגעת בגחלים אבל הטמנה על גבי גחלים לדברי הכל אסור: הגה וי"א דאפילו אם הקדירה עומדת על גבי האש ממש כל זמן שהיא מגולה למעלה לא מקרי הטמנה ושרי וכן המנהג רק שנזהרים לנתקו קצת קודם השבת מן האש כדי שיוכל ישראל להסירו משם ואם לא נתקו מן האש ומצאו על גבי האש בשבת יש להסירו משם ע"י עכו"ם ואם ליכא עכו"ם מותר לישראל להסירו משם ויזהר שיקחהו משם בנחת ולא ינענע הגחלים ואז אף אם ינענען קצת דבר שאין מתכוין שרי. (מרדכי ריש פרק כירה והגהות מיי' פרק ז'):

A Kirah is one which is constructed in the shape of a (large) kettle. Pots are placed on top of it, where it has its mouth, and there is room for placing two pots. If this Kirah was fired by means of Gefes [olive waste], or with wood, one may not place food on it to cook in the evening (on Erev Shabbos) with the intention of leaving it there (until after Shabbos arrives) – unless the food has already been fully cooked and is shrinking (i.e., continually getting bigger and smaller as a result from the cooking) to its detriment, in which case it need not be feared that the coals in the stove will be stirred. It is also permitted to place the pot on the stove if the food is raw, i.e. it has not been cooked at all. Since it is raw, one will not pay attention to it until the next morning, as it is can finish cook during the night without stoking the coals. However, if the food is cooked a little bit, or even if it is fully cooked but shrinking through cooking will benefit it, we are concerned that the coals might be stoked. Therefore, leaving it on the stove is forbidden unless the stove is raked, in other words, all the coals are removed from it or are covered with ashes, in other words the coals are covered with ashes to lessen the heat’s intensity. If a raw piece (of meat) is put into the pot, it is permitted just as if it would consist entirely of raw (meat), since now he will not pay attention to the entire pot. But even if the coals were not raked (meaning the coals were taken out of the oven) or covered with ashes (meaning the coals were covered with ashes) it is permitted to place a pot next to it, on the outside. If it was fired with straw or stubble, it is permitted to allow a pot to stay on it even if it was not Gerufa (raked from the stove) or Ketuma (the coals are covered with ashes). RAMA: If two Kirah stoves are joined one beside the other, with an earthenware partition between them: if one is Gerufa or Ketuma and the second is not Gerufa or Ketuma, it is permitted to allow a pot to stay on the one which is Gerufa or Ketuma, even though the one which is not Gerufa or Ketuma will add to its heat. However, as for a Tanur stove even if it was fueled by straw or stubble, it is forbidden to place (a pot) even adjacent to it – even if it is Garuf ve’katum RAMA as long as it is Yad soledes bo. (Haga'ot Mordechai) It goes without saying that it is forbidden to let a pot stay within it or on it. As for a Kupach-stove which has room for placing one pot on it, where it was fueled by straw or stubble, it has the status of a Kirah; where it was fueled by Gefes or wood, it has the status of a Tanur. (Our types of ovens have the status of a Kirah) (R"an). And if he forgot and left it (on the stove) if it is a Tavshil that is cooked all the way it is permitted even if it is food that improves as it condenses (called 'Mitztamech v'Yafeh Lo'). But if it is a dish that is beginning to cook and is not cooked all the way it is forbidden until Motzei Shabbos. Where one deliberately leaves a pot of food, it is forbidden in both casesRAMA: until a time period has elapsed (after Shabbos) during which the cooking done on Shabbos could be done (after Shabbos) (Ha'agahot Ashiri and Rambam). But if a Non-Jew puts it back on on Shabbos the law is the same as one who forgot and left it on (Ha'agahot Ashiri). And if a Jew puts it back on the law is the same as one who intentionally left it on. (Ha'agahot Mordechai). And if the food condensed through more cooking to its detriment it is permitted because he receives no benefit from the forbidden thing. (Beis Yosef, and see the beginning of Siman 237) There are those who say that where it has already been cooked to the degree of Ma’achal ben Derusa’i (i.e. the name of a thief who ate his food semi-cooked) or it is completely cooked and further cooking will improve it, it is permitted to leave it on a Kirah. RAMA: or even on a Tanur (HaMagid; Ha'agahot Mordechai; the beginning of the paragraph Kirah in the Beis Yosef) even one fired with Gefes (olive waste) or wood, and even if it was not Gerufa or Ketuma. In this opinion, Garuf ve’katum and firing with straw and stubble were mentioned only when the cooking process has begun but has not reached the stage of *Ma’achal ben Derusa’i;*or, where one has removed the pot from the stove and desires to return it on Shabbos. Where one forgets and leaves a pot of food, which has begun to cook, but has not reached the stage of Ma’achal ben Derusa’i, it is forbidden to eat it. It goes without saying where one intentionally leaves it there that it is forbidden to eat. RAMA: The people’s custom is to be lenient and follow this last opinion

A Kirah that is Gerufaor Ketuma, if one removes a pot from it even on Shabbos, he may return it as long as it is boiling hot Rema: and it is still in his hand (Tur) and he has not placed it on the floor RAMA: and his intention is to return it (Tur). This is specifically to the top [of the stove] but to the inside it is forbidden. It is forbidden to return [a pot] to a Tanur even if it is raked and covered up. Similarly, a Kupach when fired with Gefes [olive waste] and wood. RAMA: This is specifically when the food is fully cooked (Beis Yosef). It is then permitted to return it, even to another Kirah. But if it is not fully cooked it is forbidden even to return it to the same Kirah. There are those who say that all is forbidden only where one removes it from the Kirah while it is still day and wishes to return it after dark. However, if he removes it after dark it is permitted [to return] even if in the meantime he places it on the floor. (R"an Perek Kirah). This is our custom to be lenient for our [type of] ovens, that have the status of a Kirah, because the lenient opinion is relied upon. And it is better to be more stringent. But in all opinions where it has cooled off it is forbidden [to return it] [Beis Yosef]. There are those who say that if one removes the food from the Tanur on Shabbos it is forbidden to wrap it up in pillows or blankets. There are those who say that close to dark or close to Barchu which for us constitutes an acceptance of Shabbos (Ha'agahot Mordechai), where it is so close to Shabbos that if the pot would be cool it would be impossible to boil it up while still day, the same law (of Chazora) applies as to Shabbos itself. Some are lenient in this, and such is the accepted practice. Nevertheless it would be preferable to be stringent where there is no real need. But this refers only (to returning) directly onto a Kirah, however placing it next to it (the stove) or even next to a fire where the heat is Yad soledes bo is permitted even close to dusk. For a Tanur there is no difference between returning a pot onto it or next to it when that area is at a temperature of Yad soledes bo, but if that area is not Yad soledes it is permitted even on Shabbos, as will be stated below in Siman 318.

If one rises early (on Shabbos morning) and finds that the food in his pot is beginning to burn, if he is concerned that it might burn more, he may remove it, place a used empty pot on the mouth of the Kirah, and then put the pot containing the food atop the empty pot. One should be careful not to place the pot (containing the food) on the ground and it should be boiling hot. It has already been stated that it is customary to be lenient even where it has been placed on the ground.

One should protest against those whose practice it is to wrap up a kettle of hot water while still day (on Erev Shabbos), and then pour it into a pot of food on Shabbos when the food begins to dry out (see below Siman 318).

On Shabbos, it is permissible to place onto a pot of hot water, a dish of food that is already fully cooked such as Panades or the like, in order to warm it, since he is not cooking in a usual manner. However it is definitely forbidden to place (food) under cloths that cover a water kettle. RAMA: similarly it is forbidden to place (food) on a Kirah even if it is Gerufa and Ketuma, as the sages only permitted Chazora (but not placing a pot for the first time), as has been explained above. Some (authorities) permit placing (a pot of food) into a Tanur used for baking on Erev Shabbos, when no food was left warming in it (it was merely used for baking on Erev Shabbos), only a small amount of heat remains and there need be no concern that this will cause it (the pot) to be cooked – provided (the food) has not cooled completely. Some, however, are stringent here, and (hold that) if the heat of the Tanur is so intense that it is of Yad soledes bo, it is forbidden. See below Siman 318. One may not tell a non-Jew to do anything that is forbidden to do himself. It is therefore forbidden to tell a non-Jew to heat up the pot (of food) that has cooled. If one does so, it is forbidden to eat it even cold. [Beis Yosef and the Teshuvos HaRashba] However, if the food has not cooled below the temperature at which it is edible, it may be eaten if the non-Jew heats it up. For this reason it is common practice to have non-Jews remove pots of food from ovens in which they have been stored to retain their heat, and place them next to or on top of a heating stove, and then have the (non-Jewish) maidservant light the stove, whereupon the food will become boiling hot once again. However it is forbidden to do this through a Jew. (Terumas HaDeshen) If, however, the pots are still hot they may be placed next to the heating stove. The reason is that, as has been explained, our ovens have a status of a Kirah, and placing it next to a Kirah, which is not Garuf Ve’katum, has the same law as placing directly on top of it when it is Garuf Ve’katum (which is permitted). It has already been stated that the customary practice is to be lenient (and permit) to do Chazora [returning a pot to the stove] even if the pot has been placed on the ground. Similarly, placing (a pot) next to an oven, which is not Garuf Ve’katum (is permitted) if the food is still hot and fully cooked. It is a widespread, accepted practice to permit this. See below Siman 318.