- The Rabbinic prohibition of Shehiya is to leave a pot of food that’s not cooked on a Kirah (stove) from before Shabbat because one might come to stoke the coals. 
Different types of cooking appliances
- A Kirah was a stove in the times of the Gemara which that had room to hold two pots on top (with the heating element below). The Kirah is considered the most lenient of the stoves and it’s permissible to leave food on it on Shabbat by fulfilling one of five conditions: 1) The fire is covered 2) The food is considered totally cooked 3) The food is totally raw 4) The coals are removed 5) The fuel is straw, stubble or the like (which will be discussed below at length). 
- A modern day gas stove is considered a Kirah (and so requires one of the five requirements to be fulfilled, see further.) 
- A modern day oven is considered a Kirah (and so requires one of the five requirements to be fulfilled.) 
Covering the fire
- One is permitted to leave food on a fire if there is a metal tray or sheet to cover the fire of a regular gas stove. Some authorities add that it’s preferable to also cover the knobs (or remove them). 
- Some consider a hotplate or Plaata a covered fire and consider it an uncovered fire. 
- An oven is considered an uncovered fire unless one places a metal 4 sided box into the oven to interpose between the walls and the pot of food to serve as a reminder and some disagree holding that it’s an uncovered fire under all circumstances. 
- From before Shabbat, one may leave cooked food on an uncovered fire, Sephardim hold that the food must be fully cooked and worsens the more it cooks. However, according to Ashkenazic minhag, it’s permissible if it was cooked Machal Ben Dursai (half way). Nonetheless, Sephardim may be lenient to consider it as cooked from once it’s Machal Ben Dursai if the food is going to be eaten for Shabbat day and not Friday night. 
- Cooked food (according to Ashkenazim, half cooked and Sephardim, fully cooked, as above) may be left in an oven before Shabbat in it is on a Shabbat setting, meaning that opening the door will not activate the oven to become heated. 
- Some consider Machal Ben Dursai to be half cooked and some a third cooked. Therefore one shouldn’t leave food on the fire from before Shabbat unless it’s half cooked, however if it’s a third cooked there’s room to be lenient. 
- According to Sephardim, even completely cooked foods can’t be left on the fire unless it also worsens the more it cooks. The general rule is that any food that has flour in it is in the category of foods that worsen the more they cook, however, cabbage, beans, small pieces of meat, and egg are in the category of food for which it’s beneficial to continue cooking. If there’s a doubt considered whether something worsens or benefits from continued cooked one should be careful. 
Leaving raw food on the fire
- If the food cooking is raw meat or there’s a piece of raw meat in a the food it’s permitted to leave it on the fire from before Shabbat. 
- There’s a dispute whether our stoves nowadays fueled by oil also have the issue of Shehiya or not. Because of the old Minhag to be lenient one has what to rely on to leave food on a gas fire if the food is cooked Machal Ben Dursai and the food is meant to be eaten the Shabbat day and not that night. 
- S”A 253:1 based on Mishna Shabbat 36b with Rashi that the prohibition is based on stoking the coals.
- S”A 253:1 writes that a Kirah has the resemblance of a large pot and has room for two pots. The five leniencies listed are all sourced in S”A 253:1 but will be discussed below at length. See Laws of Shabbat (Rabbi Shimon Eider; vol 4 pg 326) for a description and pictures.
- Sh”t Igrot Moshe 1:93 considers a modern day oven to be considered like a Kirah. This is codified in Orchot Shabbat (vol 1 pg 62), Shabbat Kitchen (pg 52), Laws of Shabbat (Rabbi Shimon Eider; vol 4 pg 327) who quotes Rav Moshe and Rav Henkin..
- Sh”t Igrot Moshe 4:74:26 considers a modern day oven to be considered like a Kirah. So rules Orchot Shabbat (2:15, vol 1 pg 67), Laws of Shabbat (Rabbi Shimon Eider; vol 4 pg 327), and Shabbat Kitchen (Rabbi Simcha Bunim Cohen, pg 53). However, Sh”t Az Nidbaru 4:18 considers it be a Tanur based on the heat of a modern oven.
- Magan Avraham 253:31 permits Shehiya in an oven because the fire is covered by a cement or clay wall built into the oven based on the S”A 253:3 who permits leaving on the fire if there’s an empty vessel separating between the fire and the food. However, the Magan Avraham adds that based on the Maharil (Minhagei Maharil pg 36; see 318:15), Agudah, and Tashbetz 27 the flame must have some interposition such a wooden plank that serves as a reminder besides being covered by metal. The Achronim unanimously agree including Eliyah Rabba 253:31, Tosefet Shabbat 253:40, Shulchan Aruch HaRav 253:26, Aruch HaShulchan 253:25, Mishna Brurah 253:81, and Chazon Ovadyah (Shabbat 1 pg 50).
- According to this, a metal covering of the fire which also serves as a reminder would permit the fire to be used. Therefore, Sh”t Igrot Moshe 1:93 writes that a gas stove when covered with a metal sheet, commonly referred to as a Blech, is like a covered Kirah and is permissible. So holds Shemirat Shabbat KeHilchata 1:63 and specifies that the cover should be something that’s not usually used such as asbestos. Sh”t Zera Emet O”C 253:26, Sh”t Maharam Brisk 2:76, Sh”t Tefilah LeMoshe 1:37 (also recorded in Menuchat Ahava Ahava 3:1 in Rabbi Moshe HaLevi), Shem Chadash (on Yereyim 1 pg 58), Kaf Hachaim 253:11, Sh”t Maharshag 2:50, Sh”t Divrei Chizkiyah 1:2 in name of Mahari Shari, Sh”t Yaskil Avdi O”C 3:10(2), Sh”t Ohel Yosef (Rabbi Yosef Parid; Siman 10), Rav Vosner in Sh”t Shevet HaLevi 1:91, and Chazon Ovadyah (Shabbat 1 pg 50) concur.
- [Chazon Ish 37:9 argues on the Mishna Brurah from Rashi (Shabbat 37a D”H Gaba; quoted by the Tur) who forbids a covering over an empty space and concludes that a covering that’s not normally used and lowers the heat of the fire is considered a covering. Thus, a covering on our modern stove wouldn’t be sufficient. Chazon Ovadyah (vol 1 pg 51), Sh”t Shevet Levi O”C 1:91, Toldot Zev (Shabbat 2 pg 192) argue on the Chazon Ish that Rashi is referring to a cooking on Shabbat in a way that’s usual and so a covering it’s sufficient, however but by Shehiya one only needs a reminder not to stoke the coals and once it’s an unusual interposition it doesn’t need to lower the heat of the fire. See Bach 253:14 D”H VeDavka and Sh”t Maharam Shik O”C 117 who also make this distinction.]
- Sh”t Igrot Moshe O”C 1:93, Sh”t Tzitz Eliezer 7:17(3), Sh”t Bear Moshe vol 7, and Yalkut Yosef (Shabbat vol 1 pg 96) add that besides covering the flame it’s preferable to cover the knobs also. Orchot Shabbat (vol 1 2:9, pg 65) quotes Rav Shlomo Zalman Auerbach and Rav Elyashiv (who is also quoted by Hilchot Shabbat BeShabbato pg 197) who hold that a covering of the knobs isn’t necessary if the fire is covered.
- *Reasons to forbid a Plaata: 1) Sh”t Yaskil LeAvdi O”C 5:34, 6:15 is lenient by a covered stove since the cover is a separate piece but a Plaata is entirely like a coal and there’s nothing covering it (S”A 253:1 rules that one can’t do Shehiya with something directly touching the coals). *2) Sh”t Yaskil Avdi ibid. adds that there’s an issue that one may come to plug it in because it’s so easy unlike lighting a flame anew which the Rabbi’s didn’t make a Gezerah because it requires preparation and by that time one will remember it’s Shabbat. [Later on, he retracted because the Minhag was to use it, see Sh”t Yaskil LeAvdi O”C 7:28(8).] Arguments to permit a Plaata: *1) Chazon Ovadyah (Shabbat 1 pg 52) argues on the first reason because by a Plaata the heat comes from electric current under the metal sheet and so it’s like a covered flame. *2) Chazon Ovadyah and Netivei Am (pg 120-1) argue on the second reason, based on Sh”t Maharam Provinsal 46, and Birkei Yosef 339:7 who write that there’s no Gezerah of coming to write by composing a song as there’s a Gezerah by doing a business transaction because it may come to writing because we don’t extend the Gezerah of the Rabbis on what they didn’t just because it’s easy to come to do a Melacha. [Similarly, Rosh (Shabbat 24a), Magid Mishna (Chol HaMoad 5:20), Sh”t Rivash 390 in name of Ran, Radvaz (Trumot 1:22; Sh”t Radvaz 1:149), and Bet Yosef (O”C 462) say that nowadays the Rabbis can’t enact new Gezerah’s not enacted by Chazal.] *3) Chazon Ovadyah explains that it should be permissible since a flame is consistent (unlike coals that flicker) and the heat can’t be changed. This reason is also found is Gedolei Tzion 9:11, Mishna Brurah (Buir Halacha 253:1 D”H Afilu), Sh”t Tzitz Eliezer 7:16(3), Shemirat Shabbat KeHilchata 1:25, and Rav Yosef Kapach (commentary on Rambam Shabbat 3 pg 74).
- Halacha: Shemirat Shabbat KeHilchata 1:25 for a plaata which one can’t change it’s temperature and it’s not usually used for cooking is considered a covered fire and doesn’t require another covering. So holds Rav Moshe in Sh”t Igrot Moshe 4:74:35 (who emphasizes that it must be impossible to cook on it), Rav Vosner (MeBeyt Levi vol 6, laws of Shehiya #2) Chazon Ovadyah (vol 1 pg 52), Or Letzion (vol 2, 17:1) and Shabbat Kitchen (pg 52).
- However, Orchot Shabbat (2:13, vol 1 pg 66) and Otzrot HaShabbat (pg 100) quotes Rav Elyashiv who requires a covering of thick aluminum even on a Plaata which one can’t change its temperature.
- Magan Avraham 253:31 permits Shehiya in an oven because the fire is covered by a cement or clay wall built into the oven based on the S”A 253:3 who permits leaving on the fire if there’s an empty vessel separating between the fire and the food. However, the Magan Avraham adds that based on the Maharil (Minhagei Maharil pg 36; see 318:15), Agudah, and Tashbetz 27 the flame must have some interposition such a wooden plank that serves as a reminder besides being covered by metal. The Achronim unanimously agree including Eliyah Rabba 253:31, Tosefet Shabbat 253:40, Shulchan Aruch HaRav 253:26, Aruch HaShulchan 253:25, Mishna Brurah 253:81, and Chazon Ovadyah (Shabbat vol 1 pg 50).
- Sh”t Igrot Moshe 4:74:26 considers a modern day oven to be considered like a Kirah.
- Seemingly there’s no simple way to make an interposition for the oven in order to leave food in it before Shabbat. However, Sh”t Igrot Moshe 4:74:27 considers a metal 4 sided box to be an adequate cover and recognition. So rules the Shabbat Kitchen.
- However, the Sh”t Minchat Yitzchak 3:28(1) writes that an oven has the status of an uncovered fire even if there metal interposition based on Chazon Ish 37:11 who holds that an empty pot isn’t considered a covering (see above where many disagree with the Chazon Ish).
- The Mishna in the third perek of Shabbat (36b) says that if a Kirah (stove that’s made to hold two pots (38b)) is heated with straw or stubble, one can put food on it to cook. But if it’s heated with wood or olive peals one can’t put food on the Kirah unless one made a recognizable sign to prevent one from stoking the coals on Shabbat by having the coals Garuf (shoveled out) or Katum (covered with dust). * The Gemara (36b) asks when the mishna says not to put a food on a fire if it is heated by wood or olive peals (Lo Iten) whether it forbids returning food to a stove on Shabbat (Lo Yachzir) but it would be totally permitted to do Shehiyah (leaving food on the fire from before Shabbat) or rather it’s forbidden to leave food on from before Shabbat unless it’s Garuf or Katum (Lo Yish’heh) and certainly it’s forbidden to return food on Shabbat. There are no clear proofs in the Gemara concerning the Mishna but gives a few rulings on the issue. The Gemara has two rulings like the latter explanation, and then an opposing ruling supported by a Mishna which accords with the former explanation. * The Rif (16a) rules like the latter interpretation and so unless the stove was Garuf or Katum one can’t leave a food that wasn’t totally cooked on the stove before Shabbat. The Rambam (Shabbat 3:4), Rabbenu Yonah, Shiltot (Shlach 128), Rabbi Yehuda Barsiloni (Itim 19), and Ramban (Milchamot 15b, Chiddushim 37a D”H Mahu) concur with Rif (16a). However, Rashi (37b D”H VeRav Sheshet) rules like the former interpretation because it’s supported by a Mishna. The Rosh (Shabbat 3:1), Baal HaMoer (15b D”H Ule’inyan), Tosfot (18b D”H Bashil), Rabbenu Chananel (quoted by Tosfot 37b D”H Amar), Ran (16b D”H Tu) in name of Rav Hai Goan, Rashba (38a D”H VeHatemiha), Smag (Lav 65:13), Smak (282 pg 285), Sefer HaTrumah (231), Hagot Maimon (Shabbat 3:2), and Mordechai (Shabbat 3:299) in name of Or Zaruha (Erev Shabbat 8) concur with Rashi. * S”A 253:1 quotes the opinion of Rambam of Rif that if the stove isn’t Garuf or Katum one may not leave food on it from before Shabbat unless it’s fully cooked and worsens as it cooks and then the opinion of Rosh and Rashi that if it’s cooked Machal Ben Dursai one can leave it on from before Shabbat. Seemingly the S”A holds like Rif and Rambam since he wrote that opinion as the anonymous first ruling and only quotes the Rosh as a “Yesh Omirim” (minority opinion). Interestingly, Minchat Cohen (Mishmeret Shabbat 5) says that S”A really holds like Rosh because he didn’t make his opinion clear in 253:1 but in 254:4 he rules on another issue in favor of the Rosh. However, Erech HaShulchan 253:3, Sh”t Shoel VeNishal (1:36, 5:32), and Mishna Brurah (Shaar Tzion 254:22 in name of Pri Megadim) argue that 254:4 is a ruling that everyone would agree to and so the Minchat Cohen has no proof. There are a few approaches in the Achronim to be lenient on this issue. * Firstly, Rama 253:1 says that the Minhag is to be lenient like the Rosh. Mishna Brurah (Buir Halacha D”H VeNehagu writes that preferably one should be strict like S”A.) Therefore according to Ashkenazim, Shemirat Shabbat KeHilchata 1:63 rules that one may be lenient to leave food on an uncovered fire if the food is Machal Ben Dursai before Shabbat as long as one doesn’t intend of returning the food to the fire on Shabbat (if removed). For Sephardim, Sh”t Zechur LeYitzchak (O”C 74 pg 113a) writes in name of Maharam Ben Chaviv that Sephardim may be lenient against S”A, since it’s a Minhag from before S”A and there’s an mitzvah of Oneg Shabbat to have hot food on Shabbat. Eretz Chaim (Klal 7) supports the Zechur LeYitzchak with the Shach Y”D 242 who says a Minhag can rely a Yesh Omrim against the anonymous ruling. Sh”t Ginat Veradim 3:4, Sh”t Pirchei Cohen O”C 34, Sh”t Divrei Chizkiya O”C 1:2, Yashkil Avdi O”D 3:10, and Sh”t Vayomer Moshe O”C 3 concur based on minhag. However, Sh”t Shoel VeNishal 1:36, 5:36 argues that the Minhag is based on lack of knowledge and incorrect practices and so shouldn’t be kept. * Secondly, Sh”t Rashbatz 8 defends the Minhag to leave food that was cooked Machal Ben Dursai on a stove not Garuf or Katum because of a Safek Safeka whether halacha is like Rosh and even if not there are opinions that one can be lenient if the food is only going to be eaten Shabbat day because then there isn’t a concern of coming to stoke the coals. [Shibolei HaLeket 57 in name of Rabbenu Simcha says that Shehiya is permitted if a person has two pots and the one that’s cooking for Shabbat day is separate from the pot cooking for Friday night. Rabbenu Binyamin (quoted by Shibolei HaLeket), Mordechai (Shabbat 3:300), Rabbenu Yishaya HaRishon (Shabbat Bameh Tomnin), and Raavan (Shabbat 338) concerning Hatmana allow something that is set aside for the next day. However Bet Yosef 253:1(4) concludes that this seemingly goes against many of the Mefarshim that are brought in the following Siman.] Even though seemingly Bet Yosef should disagree with this idea of the Rashbetz, nonetheless, Bet Yosef 253:1(3) himself writes such a defense of the Minhag because of the opinion of Rashi and the possibility that one is allowed to do Shehiya for Shabbat day. Birkei Yosef 253:1 writes the same in the name of his grandfather and adds that’s it’s better to satisfy all opinions by adding a piece of raw meat (S”A 254:1) to the pot so it’s clear that the pot is cooking for the next day. Nonetheless, Chazon Ovadyah (Shabbat 1 pg 48) concludes based on the minhag and Safek Safeka of the Rashbetz a Kirah that one can leave a food cooked Machal Ben Dursai on a stove that’s not Garuf or Katum if the food is meant for the Shabbat day.
- Shemirat Shabbat KeHilchata 1:17 in the note, Orchot Shabbat (2:15 pg 67). It seems that Sh”t Igrot Moshe 4:74:26 agrees.
- Mishna Brurah 253:38
- Buir Halacha 253:1 D”H VeHu, Laws of Shabbat (Rabbi Shimon Eider vol 4 pg 344)
- S”A 253:1 writes that if the food is raw or there’s a piece of raw food in a pot it’s permissible to leave the food on the fire from before Shabbat. Mishna Brurah 253:9 specifies a piece of meat. So rules Laws of Shabbat
Removing the coals
With what stoves and how are they heated?
- A Kirah fueled with olive peals, wood chips, dung of large animals, or charcoal need to be Garuf and Katum in order to leave something not cooked upon it, however, if the Kirah is fueled with straw or stubble, one may leave not cooked food on it. <Ref> The Mishna (Shabbat 36b) differentiates between a Kirah heated by stubble and straw which don’t make coals (that can later be stoked) and a Kirah heated by olive peals, wood chips that make coals. The Tur and S”A 253:1 rule that one may leave not cooked food on a Kirah fueled by straw or stubble but if was fueled with olive peals or wood chips it’s forbidden unless the food is cooked. Mishna Brurah 253:4 in name of the Kol Bo includes charcoal in the second category of fuels. [Rambam (Shabbat 3:4) includes dung of small animals in the same category as straw and stubble, implying that dung of large animals is the category of olive peals and wood chips. However, Bet Yosef 253:1 (D”H Umasha Katuv VeIm Husaka BeKash) writes that our girsa of the Yerushalmi is that dung of small animals is included in the category of olive peals and woods. The Kolbo (Siman 31, pg 31c) also had the girsa differently from the Rambam. Mishna Brurah 253:4 rules like Rambam that dung of large animals is included in the category of olive peals and wood chips. ]
- Our stove nowadays fueled with gas or oil which don’t leave over coals seemingly shouldn’t be included in the laws of Shehiya. However some argue that since the flame that can be raised it’s forbidden because of the Gezerah just like a fire fueled with wood chips. Sh”t Panim Meirot 1:84 says a portable stovetop with a flame fueled by alcohol which can be raised by manipulation is forbidden because of the Gezerah. Sh”t Maharsham 3:165, Sh”t Amrei Yosher 2:171, Sh”t Maharam Brisk 2:76, Sh”t Esei HaLevanon O”C 11, Sh”t Shoel VeNishal 1:36, Sh”t Vayomer Boaz 18, Sh”t Divrei Chizkiya 1:2 pg 12 quoting Mahari Sharim, and Shaarei Teshuva 254:7 (D”H Mipneh) concur. [Biur Halacha 253:1 Afilu Eina Garufa who is in doubt whether it’s permissible to leave food on a Kirah that’s heated by straw and stubble only if the straw and stubble have been consumed prior to Shabbat or it’s permissible even if there’s a lot of fuel to last a long time. If so, it seems clear that the same doubt would apply to the case of a flame continuously fueled by oil.] Second source to forbid: Bear Yitzchak (Introduction to Kodshim) writes that he asked the Goan MeBrisk about leaving a container of water by an oil stove and he was answered that it’s totally forbidden as by the hot water container mentioned in Yerushalmi (Shabbat 3:3e), that forbids it since the walls of the container remain hot. Bear Yitzchak continues that Rav Zonenfeld asked Rav Yacov Elishor why he didn’t protest the Minhag some Sephardim had to leave a container of water by an oil stove and was answered that he didn’t have the power to protest this bad Minhag. Those who don’t apply the Gezerah to a modern stove: 1)Sh”t Maharshag 2:50 argues that since Chazal didn’t make a Gezerah about the case of a flame fueled by oil we shouldn’t make a Gezerah. Chazon Ovadyah (Shabbat 1 pg 48) quotes Yadei Chaim pg 200 who explains that even if something is very similar to a modern example we can’t extend the Gezerot of Chazal like the Rishonim were able to, thus modern day stoves such be permissible. Sh”t Tzitz Eliezer 2:7 (quoting Rav Tzvi Peasch Frank) based on a Yerushalmi (Shevit 2:4) concurs. 2) Sh”t Igrot Moshe O”C 1:93 distinguishes between stoking the coals for which the Rabbis made a Gezerah and adding more fuel which the rabbis didn’t make a Gezerah, and so a oil stove isn’t an issue of stoking coals and the issue of increasing the fire is permitted. This idea is applied elsewhere in Sh”t Yacheve Daat 6:20. 3) Additionally, Gedolei Tzion 9:11 (quoted by Sh”t Tzitz Eliezer 7:16(3) and Sh”t Yachave Daat 6:20) and Sh”t Kochavei Yitzchak 3:37(4) say that the Gezerah only applies to coals which constantly flicker and get close to going out, but an oil stove where the fire is constant there shouldn’t be a Gezerah. Sh”t Tzitz Eliezer 7:15(3) writes that even the Chazon Ish (Sefer Moed Siman 37) who forbids a modern stove by Chazarah didn’t even entertain the idea of forbidding it for Shehiyah. Rejection of the second source: On the other hand, Chazon Ovadyah (Shabbat 1 pg 49) rejects the proof from the Yerushlami based on Ritva (Shabbbat 41a; I searched and was unable to find this Ritva, but found it that quote in the Chiddushei Ran), who explains that water that’s totally cooked is even allowed to be left on a Kirah or a Tanur but the problem of a water container is that it was made of metal pieces and if the water evaporates one may come to add more water in fear that the fire will make the container fall apart. So writes Maginei Shlomo (Shabbat 41a) in name of Rashi. Chazon Ovadyah concludes that had Rav Yacov Elishor seen the Ritva and Poskim who permit he would have rejoiced to defend the Minhag! Sh”t Tzitz Eliezer 7:15(1) (quoting Sh”t Maharsham 3:165) also rejects the proof from the Yerushalmi because we don’t pasken like the Yerushalmi since it’s not mentioned in the Bavli.