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A. The law if the insulation does not touch the walls of the pot:
If the [pot was insulated] in a way that the clothing are not touching the pot, such as if one placed over the pot of food a wider pot which [is wide enough that it] does not touch the sides of the pot [with food] and one then placed the clothing on the [external] pot, in which case it ends up that there is no insulation involved here at all, not even with a material that does not add heat, then it is permitted to be done. [See Q&A 1 and 2]
The reason is: because the Sages only prohibited insulating with material that adds heat because of a decree that [if this were to be allowed] one may come to insulate in embers. Therefore [insulating] is not prohibited unless it is done in a way similar [to insulating with] embers, [meaning that just like embers] is moveable and is attached to the walls of the pot [so too all insulation is only prohibited if it is moveable and attached to the walls of the pot]. [Thus, being that] the walls of an oven and its opening are not attached to the pot [therefore it is not prohibited to leave a pot inside from Erev Shabbos]. ([This applies] even if the oven is small and narrow, as it is not possible that there isn’t a little bit of air separating the [walls of the oven from the pot]).
Placing an upside down pot over a hot pot on Shabbos: It is forbidden to place a vessel as a covering over a hot pot for the purpose of retaining its heat (if the pot is entirely insulated underneath the vessel), unless the vessel is wide enough to the point that its walls do not touch the sides of the pot, in which case there is no [prohibition of] insulation being done at all.
The insulating material must touch the actual walls of the pot otherwise it is not defined as insulation, and is allowed to be done even with material that adds heat.
If one insulates around a pot that has handles, and thus by the area of the handles the material is not touching the pot, is this still considered insulation?
If one has a number of pots on the Blech may he place a single towel to cover all the external sides of the pots?
According to the Alter Rebbes ruling in the Mahhadurah Basra that even insulating the top of a vessel is problematic, would it be prohibited on Shabbos to place a wide pot on top of a pot of hot food and then cover it with a towel, being that the wide pot touches the cover of the pot?
No. This is allowed even according to the Mahadurah Basra.
Ruling of Michaber: The definition of forbidden insulation is even if only a minute area of the pot is covered by the insulation material. This is called Hatmana Bemiktzas.
Ruling of Rama and Shulchan Aruch Admur: The definition of forbidden insulation is when the entire pot is fully covered with insulating material.
Ruling of Admur in Mahadurah Basra: Possibly even if only majority of the walls are covered, it is defined as forbidden insulation.
Final Ruling- How much of the pot must be insulated for it to be considered a prohibited insulation?
See above for an elaboration on the different opinions on this. The following is the final ruling as ruled by Rav Farkash in Shabbos Kehalacha.
· By material that adds heat:
Majority of the walls of the pot: One should Lechatchilah consider it to be prohibited insulation even if only majority of the walls of the pot are covered, even if its top is uncovered by the insulation material.
However by a pressing situation, or Bedieved, one may be lenient that as long as the pot is not fully covered by the insulation, such as that one covered only its walls and left its top uncovered [by the insulation, however it may have its pot cover on it], then it is allowed.
Minority of the pot: If only minority of the pot is covered, even if the cover of the pot is covered with insulation, it is allowed even Lechatchilah.
Leaving the bottom of the walls uncovered: Regarding if one may initially insulate the pot in a way that the entire bottom area of the walls is visibly uncovered, then see footnote.
· By materials which do not add heat: This is not relevant to this chapter being that insulating with such material is permitted before Shabbos. See Chapter 2 Halacha 2 with regards to the laws of insulating on Shabbos.
If the food does not fill the entire pot, is it still considered insulated if the majority area of the walls where the food reaches is insulated?
We measure against the pot itself and not against the walls of the pot that correspond to the food. Thus, even if the entire area of the food is insulated, but this area is only a minority of the pot, it is even initially allowed to be done.
What is the status of a crock pot?
It is permitted to use a crock pot on Erev Shabbos, and it does not have the status of insulation which adds heat.
The inner foil: However for this reason one must take care that when placing tinfoil on the walls of the crock pot that has more than one setting in order to be allowed to do Shehiyah/Kirah, then he may not place too much tinfoil which touches the walls of the chulent pot.
According to the stringency of the Mahdurah Basra to not cover the top of a pot on Shabbos, may one cover the top of the pots that are sitting on a Blech before Shabbos?
 Admur 257:10; Michaber 257:8
 Meaning that this type of insulation is not even considered a minor form of insulation, which is insulation with material that does not add heat.
 Thus, one may as well place a wide board or metal over the top of the pot and then cover it with clothing, as the clothing do not touch the side of the pot.
 Admur 257:4
 Meaning that the vessel completely covers the pot, both on its top and its sides, as is the case when one places a large pot over a smaller pot that the smaller pot fits entirely into the large pot.
 Meaning there is space between the walls of the smaller pot and the walls of the large pot which is sitting over it; Based on the ruling of the Mahadura Basra 259 it is also necessary that the top of the pot does not touch the top of the lower pot. [Ketzos Hashulchan 71 footnote 38]
 Shabbos Kehalacha Vol. 2 page 5
 Piskeiy Teshuvos 257 footnote 14; Orchos Shabbos 2:85; Ketzos Hashulchan 71 footnote 48 leaves the matter with a Tzaruch Iyun.
 The reason: Although he is not surrounding all the sides of each pot, nevertheless since he is doing a normal form of insulation, we therefore consider it as if all the pots together are one large pot and all the sides are hence covered over a heating material which is forbidden due to Mosif Hevel. [Ketzos Hashulchan ibid; Piskeiy Teshuvos ibid]
 Ketzos Hashulchan 71 footnote 48
 The reason: As nevertheless perhaps the Sages only forbade when the insulation is touching the sides of each individual pot and thus when there is more than one pot under the insulation it was never included in the decree. It is difficult to say otherwise as this would mean that the Sages differentiated in their decree of touching all sides between a single pot and more than one pot. [Ketzos Hashulchan ibid]
 Shabbos Kehalacha Vol. 2 page 21
 The proof: This Halacha here is going in continuation of the opinion of the Beis Yosef which holds like the Alter Rebbe in the Mahadurah Basra, and thus if according to him its allowed, then it is allowed also according to the Mahadurah Basra.
The reason: It is only problematic when one places material on top of a pot for the purpose of insulation, however when placed for another purpose, as is done here, that the upper pot is being placed in order to intervene between the towel and the lower pot, then it is allowed.
 Michaber 253:1; 257:8; Rabbeinu Chananel 37; Rashba 47b; Tur; Rosh; Peri Megadim 259 M”Z 3; Chazon Ish 37:19; See Shevisas Shabbos Hatmana 6
 Admur 253:10; 253:14; 257:4; 257:10; Kuntrus Achron 257:3; 259 Kitzur; Rama 253:1; M”A 257:18; M”B 257:69; 258:2; Shaar Hatziyon 258:9; Ketzos Hashulchan 71 footnote 29; See Piskeiy Teshuvos 257 footnote 5 and 257:11 footnote 82; Sheivet Haleivi ; In Rishonim: Or Zarua 2:8; Ravaya 197; Mordecha 299
In 253:10 and 257 10 Admur defines insulation as fully covering the entire pot with insulating material. In his words “Even if burning coals surround and are attached to the walls of the pot, [nevertheless] this is not considered [the prohibition of] insulation being that the pot is open from the top, [meaning it has no coals surrounding its top].” Similarly, in the Kuntrus Achron here number 3 the Alter Rebbe reiterates and explains this ruling, that only if both the walls and the top [meaning the pot cover] is insulated with material is it considered insulation. This ruling is also repeated here in 257:4 and in the summary of the laws of insulation brought in Chapter 259, at the very end, and is the simple understanding in chapter 253 Halacha 14. [The Sheivet Haleivi rules like this opinion, and does not make mention of the Mahadurah Basra.]
 Mahadurah Basra 259; Sefer Hayashar of Rabbeinu Tam 189; Chayeh Adam 4:22; M”B 257:43 in name of Chayeh Adam ibid; Keren Ledavid 77; Toras Shabbos 253:8; Shabbos Kehalacha Vol. 2 page 14-24; Piskeiy Teshuvos 257:11; Rav Shlomo Zalman Aurbach brought in Otzros Shabbos p. 515
In the Mahadurah Basra for chapter 259 the Alter Rebbe elaborates on the opinions which rule that by insulation which adds heat we do not take the top of the pot into account. Thus, possibly even if only majority of the walls are covered, it would be considered insulation. This opinion of Admur in the Mahadurah Basra is not mentioned in Ketzos Hashulchan chapter 71
Ruling of Mishneh Berurah: It is unclear according to the Mishneh Berurah, whether he holds like the ruling of Admur in the Shulchan Aruch, that it must all be covered to be forbidden, or if he rules like the Mahadurah Basra of Admur that even insulating majority of the walls is not allowed. [Shabbos Kehalacha 2 p. 18; See M”B 257:69; 258:2; Shaar Hatziyon 258:9 which implies that the entire pot must be covered by the insulation material. However see M”B 257:43 in anme of Chayeh Adam that implies if more than half of the walls are covered it is forbidden.]
 Shabbos Kehalacha Vol. 2 page 14-24
 This is based on the Mahadurah Basra where the Alter Rebbe brings up the possibility that this is the definition of insulation, and thus we rule Lechatchilah to be stringent like this opinion.
 This is based on the ruling in the Shulchan Aruch.
 Rav Shlomo Zalman Aurbach permits this form of insulation, even if majority of the pot is covered by its upper side. However, Rav Farkash doubts whether one may initially rely on this ruling being that it has not been brought in any of the previous Poskim.
 Shabbos Kehalacha Vol. 2 page 18; Piskeiy Teshuvos 257 footnote 5 and footnote 83
Other opinions: Some Poskim rule that we follow the food and not the pot. [Igros Moshe 4:74-4]
 Shaar Hatziyon 257:43; Shevet Halevi 9:52-53; Shabbos Kehalacha Vol. 2 page 45-47; Piskeiy Teshuvos 257:13
Other opinions: Some Poskim rule it is forbidden to use a Crock Pot on Erev Shabbos being it is considered Hatmana Shemosif Hevel. [Rav Shlomo Zalman Aurbach in Minchas Shlomo 2:34-5; See Piskeiy Teshuvos 257 footnote 95]
 The reason: As even though its pot is completely surrounded by the heating frame of the crock pot, nevertheless the frame does not actually touch the pot, being that there is always some space left between the two, and insulation is only prohibited when it touches the pot. Rav Shlomo Zalman however says that since this is the way of cooking with this machine even during the week, therefore the space in between is irrelevant and it is forbidden.
 See Ketzos Hashulchan who only records the stringency regarding Hatmana on Shabbos
 See Piskeiy Teshuvos 257 footnote 89