Permissible ways to heat up food on Shabbat
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- 1 General guidelines of Hachzara
- 2 Conditions to permit Hachzara
- 3 Returning food to non-typical heating elements
- 4 Questions
- 5 Sources
General guidelines of Hachzara
Returning food to an uncovered fire
- There is a rabbinic prohibition not to return cooked food to a fire on Shabbat even if the food is fully cooked. Some say that the reason for the prohibition is that it looks like cooking and some that it is because one may come to stoke the coals. 
- One may not return food to the oven on Shabbat even if the food is fully cooked and is very hot since an oven is considered an uncovered flame, Hachzara is forbidden. 
- If there’s a metal insert in the oven to cover over the fires, some consider the oven to be considered a covered fire. 
Moving pots around on top of a fire
- It’s permissible to move a pot from a small fire to a larger one, which is properly covered. 
- A pot was on the edge of the blech (not above the fire) may be moved to the center of the blech (above the fire) as long as the area where the pot was originally was as hot as 113 degrees and the food was fully cooked. 
Conditions to permit Hachzara
- Someone who takes food off the fire on Shabbat may return it under the following conditions:
- the food is fully cooked 
- the fire must be covered 
- at the time it was removed from the fire, one intends to put it back 
- According to Ashkenazim, the pot must remain in one’s hand or in one’s hand while resting on a table or ground, however according to Sephardim, as long as the pot wasn’t placed on the ground, one may return it. 
- According to Ashkenazim, the food (liquid and solid) should be slightly warm in order to return it to the fire, however some argue that solids don’t need to be warm at all. On the other hand, according to Sephardim, the liquids must still be 113 degrees (and solids can be cold). 
Clarification of the Second Requirement
- One may not return the inset of a crockpot to the base unless it was covered with aluminum foil (or the like) and it's preferable to cover the knob as well. 
Clarification of the fourth requirement
- According to Ashkenazim, in cases of need one may return food if it was placed on a table or bench as long as one had intent to return it a covered fire. 
- Some say that marble countertops are considered like a table or bench and if placed down there without intent, one may return it if there’s a need for the food. However, others say that marble countertops are considered like the ground and one shouldn’t return it to the fire unless there’s no other hot food. 
If some of the conditions are lacking
- If the pot was placed on a table or chair (and let go) but one had intent to return it to the fire, or one still has it in one’s hand but didn’t have intent to return it to the fire, one may be lenient if the food is needed as long as the other requirements (covered fire, fully cooked, still warm) have not been breached. 
- If one didn’t have intent to return the pot to the fire and the pot was placed on a table or chair (and let go), one shouldn’t be lenient to eat the food unless there’s no other hot food. 
- If one didn't have intent to return the pot to the fire or that the pot was placed on a table or chair (and let go), one may return a pot of food to the fire as long as the food is needed and the other four requirements are satisfied. 
Returning food to non-typical heating elements
Near a fire
- It’s permissible to place completely cooked cold solid food near a fire to remove the chill or warm it up. According to Ashkenazim, completely cooked slightly warm liquid is the same as cold solid food, while according to Sephardim, only if the liquid is completely cooked and at least the temperature of Yad Soledet Bo to be placed near a fire.
- Cold liquids that are fully cooked may not be placed in an area where if the food was left there it would reach Yad Soldet Bo unless there’s a great need, such as heating milk for a baby, and one’s intent is only to warm it or remove the chill and one actually removes it before it reaches Yad Soldet Bo. 
- One may not put uncooked food in area (near the fire) where it could eventually reach 110 degrees even if one intends to remove it from that area before it becomes 110 degrees. However, if it wouldn't reach 110 degrees even if it was left there, then it's permissible. 
- It’s forbidden to place a piece of bread close enough to the fire that it will toast. 
- It’s forbidden to dry wet clothes by placing them near a heater or radiator. 
Covered fire (Blech)
- Many poskim permit covering the fire on Shabbat with a metal tray if the flame isn’t strong enough to make the tray red-hot. 
According to Ashkenazim
- It’s forbidden to place a pot of fully cooked food on a blech (a metal tray covering the fire) even if one’s intent is just to remove it’s chill.  However, many permit placing fully cooked food on a blech on the area where it doesn’t reach 113 degrees. 
- Some say that it’s permissible to put foods on the blech on shabbat which could not be cooked on the blech (such as challah or kugel) as long as one doesn’t put it on the area which is over the fire. 
- One may move pots from a cooler area to a warmer position on the blech only if the food is fully cooked and the area from which it stood originally was 113 degrees. 
According to Sephardim
- According to Sephardim, it’s permissible to put a solid completely cooked food on top of a blech or hotplate on Shabbat.  However, it is forbidden to put a cooked liquid on a blech or hotplate on Shabbat unless one fulfills the conditions of Hachzara, however it is permissible to ask a non-Jew to put a cooked liquid on top of a blech or hotplate on Shabbat. 
One pot on top of another
- One may place cold fully cooked solid food on top of a pot that is on the fire on Shabbat because that is not considered on top of a fire at all.  According to Sephardim, a fully cooked liquid, which is also at least Yad Soledet Bo is the equivalent of a fully cooked solid food, according to Ashkenazim, a fully cooked liquid which is at least slightly warm, is the equivalent of fully cooked solid food. 
- Note that this leniency only applies if the bottom pot is filled with food and not if it is empty. 
- If the food isn't fully cooked, one may not place the food on top of another pot which is on the fire  unless there's no chance that the pot will reach Yad Soldet Bo if it was left there. 
- It’s forbidden to place a pot on top of another pot where the top pot contains food with containing large quantities of congealed fat. However, if there’s only a little congealed fat such that when melted it mixes with the rest of the food it’s permissible. If fat was dissolved it may be eaten. It’s also permitted to dissolve a sauce that is normally eaten in its congealed state such as fish sauce. 
- Some say that placing food on a “Kedeirah Blech,” a rectangular box filled with water placed on top of the fire before Shabbat, is the same as placing food on top of a pot on the fire, while others say that it merely like a covered fire, to which one may not return food without fulfilling certain conditions (see the #Covered_fire_(Blech) section). 
- Many authorities permit placing food on an electric hotplate which does not have an adjustable temperature setting, even without fulfilling the conditions of Hachzara, since it is not a usual way of cooking. However, others say that it is considered like a covered fire, upon which one may not return food without fulfilling the conditions of Hachzara. 
- In order to return food to a crockpot or the crockpot insert back into the electric setting the conditions of insulating (hatmana) and returning (hachzara) must be met (as described above). 1) If the insert pot is raised such as with marbles or the like then there's no issue of hatmana. 2) The food must be cooked. 3) The heating element must be covered such as by covering the surface with aluminum foil which then extends upwards and is seen before the adjustable setting. 4) At the time it was removed one's intent was to return it. 5) The pot remained in one's hands. 6) The food remains slightly warm. If it is a liquid, according to Sephardim it must be Yad Soledet Bo.
- Some say that one may leave fully cooked food in a crock-pot which is on a timer (set from before Shabbat) to turn on Shabbat morning and off Shabbat afternoon, however, some question this. 
- Some poskim permit placing fully cooked solid food in a warming drawer if one turns it on the low setting, which it can't be used for cooking, and the knob to adjust the temperature is covered, while others forbid (see below for details). Some of the stringent opinions would permit if there's no knob to adjust the temperature.
The opinion of the Ran
- Some say that if solid food was on the Blech during Bein HaShemashot and was removed on Shabbat, it may be returned to a covered fire on Shabbat as long as it is fully cooked, while many others reject this leniency. 
- May one return cold fully cooked food to a blech on Shabbos? See the #Covered fire (Blech) section above.
- May one return cold fully cooked food to an electric hotplate on Shabbos? See the #Electric Hotplates section above.
- May one return cold fully cooked food to an Kedierah Blech on Shabbos? See the #Kedierah Blech section above.
- The Mishnah (Shabbat 36b) records Beit Hillel’s opinion that one may not return a pot to a Kirah (type of stove meant to hold two pots) on Shabbat if the Kirah is heated with pressed sesame or wood unless the coals were covered with ashes or removed.
- Rashi Shabbat 36b "lo machzirim" says its "mechzay kimivashel", meaning, that the reason Chazal prohibited placing fully cooked food on the fire on Shabbat is that it looks like one is cooking on Shabbat. Baal HaMoar 16b, Rashba (38b s.v. MeKlal) in name of some geonim, Ritva (40b s.v. VeAskina), and Ran (17b s.v. Bei Rav Ashi) write that the prohibition of Hachzara is a gezerah of Chazal because it looks like cooking when one heats up cold food on Shabbat. Mishna Brurah 253:55 quotes this Ran.
- Rabbeinu Tam Sefer Hayashar 235 adds that Chazal prohibited it lest a person stoke the coals on Shabbat. Shaar HaTziyun 235:37 quotes this opinion of the Rabbeinu Tam.
- The Gemara and Rishonim discuss under what conditions may one return food to the fire. Based on the Rama 253:2, Shemirat Shabbat KeHilchata 1:18 rules that one may return food to a fire on Shabbat only under the following conditions: 1) the food is fully cooked, 2) it’s still somewhat hot (see the footnotes to #The opinion of the Ran about which foods need to be somewhat hot), 3) it was removed with intent be to returned, 4) one kept his hand on it, and 5) the fire is covered. For the slightly variant conditions according to Sephardim, see Yalkut Yosef 253:9.
- Shemirat Shabbat KeHilchata 1:17
- Sh”t Igrot Moshe 4:74:27 permits returning food to an oven on Shabbat if the oven has a metal insert of 4 sides to serve as a reminder. However, Sh”t Shevet HaLevi 3:48 argues on Igrot Moshe and holds that under all circumstances it’s forbidden to return food to the inside of an oven.
- Shemirat Shabbat KeHilchata 1:21
- Shemirat Shabbat KeHilchata 1:22
- S”A 318:4 and Rama 253:2 rule like the Rambam and Tur who hold that unless foods are fully cooked one would violate Bishul Deoritta, against the Rosh (Shabbat 3:10-11) and Rashba (Shabbat 18b) who hold that once food is cooked KeMachal Ben Dursai it’s permissible to cook it even until it’s fully cooked food. Therefore, one may not return to the fire any food that’s not fully cooked otherwise there’s a potential Deoritta violation of bishul. Accordingly, Biur Halacha 318:4 D”H Shayach writes that even if one is in doubt whether the food is fully cooked or not one may not return the food to the fire. So brings Shemirat Shabbat KeHilchata 1:18 note 55.
- S”A 253:2 writes that one may return hot food if the fire is Garuf or Katum. Mishna Brurah 253:81 adds that a similar metal try can be used as a cover of the fire to separate the fir from the pot. Similarly, S”A 253:3 writes that if on Shabbat morning one finds the food in one’s pot burning, one may remove it from the fire, put an empty pot on the fire and then the pot with food in it on top of the empty pot. Mishna Brurah 253:81 comments that it’s permissible to put the pot back on the fire since there’s an empty pot on the fire making it like Garuf or Katum. Kaf HaChaim 253:11, Sh”t Maharshag 2:50, Sh”t Igrot Moshe 1:93, and Shemirat Shabbat KeHilchata 1:18 rule that the fire must be covered in order to do Hachzara (Shemirat Shabbat KeHilchata (1 note 54 quotes Rabbi Shlomo Zalman as saying that one shouldn’t increase the flame when one puts a cover on top of it). Many poskim including Mishna Brurah 318:91, Shemirat Shabbat KeHilchata (chapter 1 note 59) in name of Rav Shlomo Zalman, and Sh”t Igrot Moshe 1:93 rule that one may cover the fire on Shabbat even if the pot is metal against Chazon Ish 37:11 who forbids putting metal on fire where it’ll become 113 degrees.
- Rama 253:2 in name of the Tur rules that one must have intention to return the food to the fire when one takes it off. Shemirat Shabbat KeHilchata 1:18 agrees. Mishna Brurah 253:56 writes that if one still has the food in one’s hand but didn’t intend to return it to fire, one can be lenient in cases of need.
- Rama 253:2 writes that one of the conditions of Hachzara is that one keeps the pot in one’s hand. Mishna Brurah 253:55 writes that it’s forbidden to return the pot even if one put it down on a table or bench. The Shemirat Shabbat KeHilchata 1:18 writes that if one keeps one hand on the pot as one rests in on a table one may return the pot to the covered fire. Many achronim including Torat Shabbat 253:11, Demesk Eliezer 253:11, Sh”t Igrot Moshe 4:74:33, and the 39 Melachos (vol 2 pg 619, by Rabbi Ribiat) rule that as one as one keeps one’s hand on the pot even if the pot was rested on a table or bench one may return the pot. [However, from the Biur Halacha 253:2 D”H Velo it seems not like this.] On the other hand, S”A 253:2 writes that one of the conditions is to make sure not to place the pot on the ground. Magen Avraham 253:20 writes that the S”A argues on the Rama and permits leaving it on a table or bench if one intends to return it to the fire. Thus, Yalkut Yosef (Shabbat vol 1 pg 103) writes that there’s no requirement to have the food in one's hand.
- S”A 253:2 writes that a condition of Hachzara is that the food is still boiling meaning that it’s 113 degrees. This condition is referring specifically to liquids as the Mishna Brurah 253:54 explains that this condition is dependant one of bishul and not Hachzara. Since S”A 318:4 rules that a liquid may not be heated up once it’s not 113 degrees, so too here a liquid may not be put back on the covered fire unless it’s 113 degrees. However, Rama 253:2 and 318:15 writes that Ashkenazim are lenient to allow returning a fully cooked liquid as long as it’s now slightly warm. This is also the opinion of Mishna Brurah 253:54 and Shemirat Shabbat KeHilchata 1:18. Regarding solids, the Magen Avraham 253:36 writes that it also must be somewhat warm in order to return it to the fire. However, the Beiur Halacha 253:5 s.v. Ubilvad argues on the Magen Avraham based on the Buir HaGra. [It seems that Mishna Brurah 253:54, 91 rules like the Gra against the Magen Avraham even though he quotes the Magen Avraham (in 253:68).] The Shemirat Shabbat KeHilchata 1:18 seems to rule like the Magen Avraham, however, it’s unclear what he holds based on the footnote. Yalkut Yosef (Shabbat vol 1 pg 103) and Menuchat Ahava (3:2, vol 1 pg 50) agree with the Beiur Halacha that one may be lenient like the Gra.
- Shabbos Kitchen (Rabbi Simcha Bunim Cohen, p. 60)
- Beiur Halacha 253:2 s.v. VeDato writes in cases where one had intent to return the pot to the fire, and left it on the ground, in a case of need there’s room to be lenient. Shemirat Shabbat KeHilchata 1:19, Orchot Shabbat (vol 1 pg 85) agree. (It seems, however, that the Orchot Shabbat quotes Beiur Halacha even in cases where there’s no need).
- Regarding placing a pot on a marble countertop there’s a dispute in the poskim. Petach Dvir 253:2, Sh”t Yitzchak Yiranen 2:42, and Menuchat Ahava 3:2, 3:8(3) write that anything attached to the ground is considered like the ground. Yalkut Yosef (Shabbat vol 1 pg 193 note 9) says that one has what to rely on if it was left on marble and not on the ground itself. Orchot Shabbat 2:46 brings a dispute between Rav Elyashiv, Rav Shlomo Zalman, and Rav Nassim Karlitz who are lenient regarding marble counters while, Rav Wosner is strict on this issue.
- Beiur Halacha 253:2 s.v. VeDato (and Mishna Brurah 253:56) writes that if necessary (Shat Tzorech) one can rely on the Rishonim who say one doesn’t need intent if it’s still in one’s hand or one doesn’t need it in one’s hands if one has intent. Shemirat Shabbat KeHilchata 1:19 agrees.
- Shemirat Shabbat KeHilchata 1:20
- Shemirat Shabbat KeHilchata 1:19
- Nonetheless, the Ran 19a writes that one may place a cold fully cooked food near the fire on Shabbat even in an area where it can reach Yod Soldet Bo because it is not considered a normal way of cooking. The Bet Yosef 318:15 limits this leniency to a fully cooked solid food, but a cold liquid may not be heated up near the fire because it is considered Bishul according to many opinions. Thus, S”A 318:15 rules that one may place a cold fully cooked solid or boiling liquid near the fire even in an area where it may become Yad Soldet Bo. Mishna Brurah 318:96 explains that according to Shulchan Aruch the liquid only needs to be Yad Soledet Bo and not actually boiling. (Whether the liquid needs to be completely cooked besides for being Yad Soledet Bo, see footnote about Bishul Deoritta.) Rama 318:15, however, writes that the Ashkenazic minhag is to be lenient regarding reheating cooked liquids as long as it’s slightly warm. Shemirat Shabbat KeHilchata 1:13 and Shabbos Kitchen (pg 43) agree.
- Shemirat Shabbat KeHilchata 1:13
- 39 Melachos (vol 2 pg 563), Shemirat Shabbat KeHilchata 1:13
- Shemirat Shabbat KeHilchata 1:62
- Shemirat Shabbat KeHilchata 15:9-11
- Sh”t Zera Emet 3:26 permits one to put a metal tray (with small holes) on a fire on Shabbat and then do Hachzara based on S”A 318:8 where he brings the dispute whether one can do Hachzara on an empty over the fire and rules like the lenient opinion. Chazon Ish 37:11 argues that actually placing the metal sheet on the fire is the forbidden act of Mavir based on Rambam (Shabbat 12:1, 9:6) who says that one who heats metal to mold it violates Mavir. Even though S”A 253:3 writes that on Shabbat day one can put a empty pot on a fire (and then return a pot that was on the fire right before), Chazon Ish explains that S”A is talking about a earthenware pot and not metal. However Nishmat Adam 20:1, Kesot HaShulchan (134 pg 42), Sh”t Shevet Halevi 1:91, Sh”t She’ilat Shaul 29, Chazon Ovadyah (Shabbat 1 pg 55), and Sh”t Tefilah LeMoshe 1:59 (pg 647) argue that in our case the tray won’t become hot as a coal or hot enough to be reshaped and so it should be permitted. Shemirat Shabbat KeHilchata 1:23 and 1:38 permits covering the fire on Shabbat as long as the fire isn’t strong enough to make the tray red-hot.
- Shemirat Shabbat KeHilchata 1:25, Sh”t Igrot Moshe 1:94, Shabbos Kitchen (pg 44), 39 Melachos (vol 2 pg 564)
- Shabbos Kitchen pg 44, Igrot Moshe 1:94. However, Az Nidabru 8 forbids even in an area where the blech will not reach Yad Solet Bo.
- 39 Melachos (vol 2 pg 564) quoting Rav Shlomo Zalman
- Shemirat Shabbat KeHilchata 1:25
- Rabbi Mansour on Dailyhalacha.com, Yalkut Yosef (Shabbat vol 3 pg 207)
- Rabbi Mansour on Dailyhalacha.com, Yalkut Yosef (Shabbat vol 3 pg 207)
- The Tosefta (Shabbat 3:23) permits placing a pot of food on top of another pot (Kedeirah Al Gabei Kedeirah) on Shabbat in order to preserve the heat of the top pot but not in order to heat it up. The Bet Yosef 258 quotes Rabbeinu Yerucham, who cites the Rosh’s opinion that the requirement that the food be hot is true only regarding foods that weren’t fully cooked or liquids, but a cold fully cooked solid may be placed on top of a pot on Shabbat. Rabbeinu Yerucham then quotes a second opinion that placing cold food on top of a pot is like placing it on a fire which is forbidden. S”A 318:8 rules like the Rosh. Many achronim including Gra 318:7, Eliyah Rabba 318:21, Mishna Brurah 318:60, Shemirat Shabbat KeHilchata 1:36, and Yalkut Yosef (Shabbat vol 3 pg 207) agree.
- Additionally, Rabbenu Yerucham quotes a dispute whether this leniency applies even if the bottom pot is on the fire, or only if it isn’t on the fire. S”A 318:7 quotes these two opinions without ruling. Magen Avraham 318:24 and Mishna Brurah 318:55 rule like the first opinion. Thus, Shemirat Shabbat KeHilchata 1:42 rules that one may place cold fully cooked solid food on top of another pot of food that is on the fire, even if it will become Yad Soldet Bo. Shabbos Kitchen (p. 41-2) and Orchot Shabbat (p. 99) agree.
- Even though Shulchan Aruch 318:7 writes that liquids must be as hot as Yad Soldet Bo, Rama 318:15 argues that even if it’s just slightly warm it’s permissible. Shemirat Shabbat KeHilchata 1:36 agrees.
- Shulchan Aruch 318:8 rules that one may place fully cooked cold food on top of another pot on the fire. On the other hand, the S”A 253:3 rules that one may return food on top of an old pot only if the food is still hot and wasn’t placed on the ground, implying that placing food on top of another pot isn’t permitted without the conditions of Hachzara. The Pri Megadim E”A 253:33 answers that the leniency spoken about in 318:8 only applies if the bottom pot is filled with food, and not if it is empty. Bei’ur Halacha 253:3 s.v. Veyezaher, Chazon Ish 37, Sh”t Az Nidbaru 3:14, and Shabbos Kitchen (Rabbi Simcha Bunim Kohen; pg 42) agree that the bottom pot must be filled with food. See, however, Sh”t Shevet HaLevi 1:91.
- See Shemirat Shabbat KeHilchata (chap 1, note 126) who writes that if the empty pot isn't on top of the fire directly but rather on top of a tray which covered the fire, then one may place fully cooked solid food on top of the empty pot because that's considered like a pot on top of a pot. Piskei Teshuvot 253:25 agrees. Also, Orchot Shabbat (p. 100) writes that some permit placing fully cooked cold food on top of an empty pot on top of an electric hot plate. However, Rav Mordechai Willig in Am Mordechai (p. 30) disagrees because there should be no difference between one blech and two or a flat blech and a crooked blech.
- S”A 318:7-8 quotes a dispute whether one may place a pot with cold solids or hot liquids which are Yad Soldet Bo on top of a pot that’s on the fire and rules leniently. Even though the Taz 318:11 writes that it’s permissible even if it’s not fully cooked (but seems to require that the pot will not be able to cook), Mishna Brurah 318:55 rules that the food must be fully cooked based on many Achronim (Bach, Gra, Tosefet Shabbat, Olat Shabbat, Maamer Mordechai, Pri Megadim) who disagree with the Taz 318:9 on a similar issue. Shemirat Shabbat KeHilchata 1:36 rules like the Mishna Brurah.
- Beiur Halacha 318:6 s.v. Ad SheTehe, Shemirat Shabbat KeHilchata 1:36
- Shemirat Shabbat KeHilchata 1:37
- A “Kedeirah Blech” is a covered rectangular metal box containing water that is meant to serve as a “pot” on top of the fire upon which pots can rest. Rav Hershel Schachter (“Hilchos Bishul B’Shabbos”, min 56-9) rules that a “Kedeirah Blech” is like a pot on top of a pot and is permissible. Rav Mordechai Willig (Am Mordechai p. 28), though, argues that since the water inside the “Kedierah Blech” isn’t meant to be consumed, it is not similar to the case of a pot on top of a pot. His opinion is also explained in English in "Cooking and warming food on Shabbat" p. 108. Rabbi Elyashiv (cited by The 39 Melachos Bishul note #212), Rabbi Belsky (39 Melachos Bishul note #211; on ouradio.org, “Cooking on Shabbos- A HOT TOPIC”, min 60-68), and Rabbi Dovid Cohen (oukosher.org) agree.
- Shevet HaKehati 4:110 and Az Nidbaru 1:38 say that a pot inside a pot isn’t considered a Kedeirah Al Gabi Kedeirah. Shemirat Shabbat KeHilchata (chap 1, note 118), 39 Melachos (regarding a double boiler), and Piskei Teshuvot 253:25 agree. Note that this is a case of a pot inside of a pot, such as a double boiler, but isn't the same as the Kedeirah Blech.
- Rav Mordechai Willig (Am Mordecahi p. 48) writes that one may heat up cold fully cooked solid food on an electric hotplate which is not used for cooking and has only one temperature setting. Halachos of Shabbos (p. 313), Shabbos Kitchen (p. 43), and Chazon Ovadyah (p. 78) agree. See Sh”t Igrot Moshe 4:74:35 who rules that if it is impossible cook on a particular electric hotplate, one may heat up already warm food on it if it has only one setting. Shemirat Shabbat KeHilchata 1:30, however, rules that an electric hot plate is a like a covered fire and one may not return food onto it without fulfilling the other conditions of Hachzara. (Rabbi Neuwirth emphasizes this in his approbation of Am Mordechai (p. 7).) Rabbi Belsky (quoted by Halachically Speaking 4:16:3) and Orchot Shabbat (p. 99) agree.
- Chazon Ovadyah (Shabbat 1 pg 55) holds that since Hachzara is only forbidden as it looks like cooking a plaata (electric hotplate) which isn’t used for cooking should be permitted for Hachzara. Rav Frankel (Kol Torah (Iyar 5723, Sh”t Har Tzvi O”C 136, Toldot Zev (Shabbat 2 pg 234)) concurs. Sh”t Igrot Moshe (O”C 4:74(35), 1:93) permits Hachzara on a blech if the food is fully cooked because it’s not used to cook and being a blech for Shabbat it serves as a reminder it’s Shabbat. Sh”t Yashkil LeAvdi O”C 7:28, Rav Shlomo Zalman Aurbach (Shulchan Shlomo 253:27), Sh”t Tzitz Eliezer 8:26, Chukei Chaim Peretz 8 in name of Rav Sheinberg, Sh”t Me’oneh Lashon 22, Sh”t Tefilah LeMoshe 1:32, and Yitzchak Yiranen (pg 50) concur to permit Hachzara on a plaata. However, Yashiv Moshe (Rabbi Twersky pg 36) in name of Rav Elyashiv and Sh”t Avnei Yishfeh 1:83 are strict because a plaata is sometimes used to cook. See also Sh”t Shemesh UMagen 1:53 and 3:54(3).
- See Halachos of Shabbat (p. 313) who rules that one may place food on a radiator. See also Shemirat Shabbat KeHilchata 1:30, who argues that a radiator is like a covered fire upon which one may not return food to it on Shabbat without fulfilling the other conditions of Hachzara.
- Rabbi Willig in The Laws of Cooking and Warming Food on Shabbat p. 126 quoting Rav Elyashiv. See Orchot Shabbat p. 540
- Rabbi Willig in The Laws of Cooking and Warming Food on Shabbat p. 124
- Rabbi Hershel Schachter (OU Kosher Webcast, min 13-16) says that even though the Shemirat Shabbat Kehilchata is lenient there is room to be strict because the Chazon Ish had a doubt about this.
- Rabbi Gedalia Schwartz (Sappirim 5768, Issue 6) ruled that one may place food in a warming drawer if they are set to the low setting so that they aren’t used for cooking and the knobs are removed or covered. He notes that this only applies to solid completely cooked food.
- Rabbi Belsky (on ouradio.org, “Cooking on Shabbos- A HOT TOPIC”, min 6-8) says that essentially it may be permitted to use a warming drawer on Shabbat which looks different than other warming drawers and only reaches temperatures of 175 degrees, but doesn’t conclude that it is actually permissible, because it is too similar to other warming drawers. However, if the warmer drawer is adjustable or it could reach temperatures of 275 degrees it is certainly forbidden.
- Rabbi Muschell (star-k.org) writes that if the warming drawer reaches above 120 degrees one may not place food in there on Shabbat. Rather he writes that one may leave food in there from before Shabbat on a few conditions. If the temperature is adjustable the knob must be covered. If opening the warming drawer is thermostatically controlled one may only open the drawer once on Shabbat, removing everything at one time. Similarly, on another page, the Star-K writes that all food should be placed in the drawer before Shabbat and may not be placed there on Shabbat. The drawer may be opened only once and so one should remove all food at one time. Additionally, the Star-K writes, that one should cover the knobs and the temperature certainly may not be adjusted on Shabbat.
- Rabbi Mordechai Willig ("The Laws of Cooking and Warming Food on Shabbat" p. 127) writes that reheating cooked food in a warming drawer is permitted since it doesn't look like cooking. However, the knobs must be covered so that it is extremely inconvenient to adjust the temperature. Rav Hershel Schachter (ibid. p. 181) argues that covering the knob is insufficient unless there is no knob to adjust the temperature.
- The Ran (Shabbat 17b) infers from the Yerushalmi that if food was on the fire from before Shabbat and was removed only once Shabbat began, it may be returned without all of the conditions of Hachzara. Bet Yosef 253:2 writes that many Rrishonim, including Tosfot, Rosh, and Rambam, disagree with the Ran. Nonetheless, the Rama 253:2 records the minhag to rely on the Ran but advises one to be strict. Mishna Brurah 253:63 explains that this leniency only removes the conditions of intending to return the food and keeping it in one’s hand; the food would still have to be fully cooked and placed on a covered fire.
- Magen Avraham 253:36 writes that besides for the other conditions of Hachzara it is only permitted to return a solid food to a covered fire if it is not completely cold because otherwise it looks like one is cooking on Shabbat. Bei’ur Halacha 253:5 s.v. UBilvad, however, explains that the Gra argues that only liquids need to be warm in order to be returned, but solids may be returned even if they are cold. Shemirat Shabbat KeHilchata 1:20 and Sh”t Igrot Moshe 4:74:31 rule like the Magen Avraham, while Chazon Ovadyah (p. 80) agrees with the Gra. Mishna Brurah 253:67 defends the minhag to some degree. Chazon Ish dissapproves of relying on this leneincy. Rabbi Shimon Eider (Halachos of Shabbos, chap 14, sec F, pg 355) rules that one should not rely on this lenient ruling and writes that the Mishna Brurah's defense wouldn't apply nowadays.
- Rav Soloveitchik (cited by Rabbi Jachter in “Hachzara and Hatmana”, koltorah.org) ruled that one may rely on the Ran. (This ruling of Rav Soloveitchik is also recorded in Halakhic positions of Rabbi Joseph B. Soloveitchik, (Rabbi Zeigler, vol 4, pg 90-1) and by Rabbi Michael Taubes.) This is also relying on the Gra’s opinion that only liquids need to be warm. Rav Mordechai Willig (Am Mordechai p. 47), however, rules that initially one should not rely on this lenient ruling. Rav Hershel Schachter (“Hilchos Bishul B’Shabbos”, min 52-5), Shemirat Shabbat KeHilchata 1:23, 39 Melachos (Bishul #203), and Halachos of Shabbos (p. 355) agree.
- Rabbi Dovid Miller in explaining the topic emphasizes that Rav Soloveitchik only permitted reheating fully cooked solid food but not liquids or soup.