Placing a cooked food on an oven very close to Shabbos, without enough time for it to heat up:
The above discussion in chapter 1 only referred to initially placing a pot of uncooked food on the fire before Shabbos and having it stay there until after Shabbos begins without removed it in the interim. However if one already began cooking the food and then removed the pot before Shabbos, even if one had cooked it and removed it the day before, and now decided to return it close to the beginning of Shabbos, then the following other laws apply.
1. The law:
First Opinion: A cooked food may be returned to a fire before Shabbos, even inside a freshly lit Tanur of those days. This may be done even minutes before the entrance of Shabbos, being that the food is already cooked and thus does not have the Shehiyah restriction apply to it.
Other Opinions: However there are opinions which say that when it is so close to Shabbos that if the food in the pot were to be cold then it would not be possible to heat up before Shabbos, it is forbidden to return it to a fire, even if now the food is hot, unless all the Chazara conditions are fulfilled in a way that would thus permit one to return this food even on Shabbos itself.  [See Q&A 1-5] [Regarding what are the Chazara conditions, see the next chapter which deals with these Halachas.]
Their reasoning for requiring this is: because of a decree that [if this were to be allowed then] perhaps one will come to return a food even on Shabbos itself. [As if one were to be allowed to allow the food to heat up on Shabbos, even though he placed it there before Shabbos, then perhaps one will not differentiate between when the food is placed there and come to allow to place the food there on Shabbos itself in order to heat up, without fulfilling the Chazara conditions.]
The Final Ruling: The custom is to be completely lenient like the first opinion, however in a situation where there is not much need for one to do so, it is proper to be stringent to not place the pot on the oven if there is not enough time for it to heat up before sunset, unless the Chazara conditions are fulfilled. For this reason it is proper to be careful to not remove the pot off from the Kirah or the Tanur which it was cooked in and place it [On Erev Shabbos] close to sunset, on a heater, which is not swept or covered, if it that area is Yad Soledes there. [This however is] with exception to if one places something under the pot, just like one is required to do on Shabbos itself, as will be explained [in Halacha 26].
2. If there is enough time for the food to be heated before Shekiah, but not before one accepts Shabbos:
If when one comes to return the food to the flame there is enough time to heat it up before Shabbos [meaning Shekiah] but there is not enough time to heat up before he personally accepts Shabbos, then according to all opinions there is no prohibition involved to place the food on the fire without the Chazara conditions being fulfilled, so long as there are no Shehiyah prohibitions involved.
3. Placing the pot near the oven close to Shabbos:
To place a food near the fire of a Kirah oven, even if it is Yad Soledes in that area, is permitted according to all opinions in all cases, and neither the Shehiyah or Chazara restrictions apply. This is despite the fact that there are those which prohibit this to be done on Shabbos itself without the Chazara restrictions being fulfilled.
4. Placing raw meat on the fire before Shabbos according to the stringent opinion:
If the food [contains meat which] is completely raw, it is allowed according to all opinions to even return it onto a Kirah which is not swept or covered, close to Shabbos [sunset] itself. As by raw [meat] we are not worried at all that one may come to stoke the fire, as was already explained [in 253/8].
Summary of the laws of placing a food by a fire close to Shabbos:
A. Near a fire:
Tanur of back then/Kupach of wood fuel: Is forbidden unless the food is cooked to the point of Ben Drusaiy, or is completely raw.
Kirah oven: It is permitted under all circumstances, according to all opinions to place a food near the oven, even if the food has already begun cooking, but is not yet Ben Drusaiy.
Stove/Electric plate: If it is placed very close to the fire/heat it has the same law as when placed on a fire, which is explained next.
B. On a fire:
If there is enough time for the food to be heated before Shekiah: Then only the restrictions of Shehiyah apply [I.e By today’s stoves: either fire is covered or food is completely raw or cooked to point of Ben Drusaiy.]
However if there is not enough time for the food to be heated before Shekiah: Then initially one should be stringent to also require the conditions needed for “Chazara” in addition to the conditions required for Shehiyah, with exception to if meat is completely raw, in which case according to all opinions it is allowed without restriction, for all ovens. In a time of need however one need not be stringent to require also the conditions of Chazara, and if the conditions of Shehiyah are fulfilled, it is allowed.
If the food is half cooked but not yet fully cooked must it still be placed on the fire with enough time to heat up before Shabbos according to the stringent opinion?
This matter is disputed in Poskim. Practically even if the food is not fully cooked one is to be stringent like the stringent opinion.
Does the above stringency apply even to food being placed on a covered fire for the first time?
No. It only applies to food which was on the fire and then removed, and now one wants to put it back on. Thus one may place uncooked food any time before Shabbos on a covered flame according to all opinions.
Does the above stringency apply even when placing food on an electric plate?
There is room to allow one to be completely lenient by an electric plate.
If one places the food on a high flame, does he have to leave it on the high flame until it heats up, or can he lower the flame even before it gets a chance to heat up before Shabbos?
Some Poskim rule that if the pot was placed on a fire that could heat it up before Shabbos, then one may afterwards lower the fire, even before it has heated up.
Practical ramifications of the above stringency:
- Chullent in Crockpots: When returning the chulent pot back into the crockpot before Shabbos one must make sure it is done early enough for it to technically be able to heat up if it were to be cold. Being that crock pots are slow heaters, therefore this may practically need to be done hours before Shabbos. Thus one should either a) return the chulent to the crock-pot before this time or b) not remove the Crockpot without all the Chazara conditions within this amount of hours before Shabbos.
- Food on the Blech/electric plate: Practically unless one plans to have all the conditions of Chazara fulfilled one should not set up the blech very close to Shabbos. Rather one is to do so early enough so that if all the foods were cold they would be able to heat up by the time Shabbos begins. At the same time one needs to be careful once the food is placed on the blech that it not be removed unless all the conditions of Chazara are planned to be fulfilled.
- Practical advice: In a situation that one forgot to set up the blech or crock pot with enough time, he can still keep to the stringency by doing the following. Heating up all his foods on a high flame and then transfer it with all the conditions of Chazara onto the Crockpot and blech/electric plate.
 Not cook. Meaning as long as it could heat up before Shabbos, even though that to cook it, if it were theoretically to be uncooked, would take a lot longer, it is still valid even according to this opinion. [Shabbos Kehalacha Vol. 1 page 379]
 Meaning they hold that from before Shabbos, when there is no longer enough time to heat up the food if it were to be cold, then all the restrictions of returning a food on Shabbos begin to apply. This is according to the Alter Rebbe, and so rules the Olas Shabbos on the Rama.
Other Opinions: The Gra and Tosefes Shabbos hold the stringency is only with regards to requiring to cover the flame before Shabbos if there is not enough time to heat it up by the time Shabbos begins, however all the other restrictions of intention etc. are not needed even according to the stringent opinion. The Mishneh Berurah rules like this latter opinion. [Shabbos Kehalacha Vol. 1 page 381]
 Lit. Good
 Lit. Good
 Shabbos automatically begins at sunset, whether or not one has consciously decided to accept Shabbos. Although, one who wants, may accept Shabbos earlier then sunset. Thus the novelty here is that as long as there is enough time for the food to heat up before sunset, he may place it on the oven according to all opinions, even if he will be accepting Shabbos earlier than sunset and the food will not be able to be heated by that time. [Magen Avraham 253/26.]
Other Opinions: However the Rama there learns that according to the stringent opinion, the food must be able to warm prior to one’s personal acceptance of Shabbos.
 Tzaruch Iyun why the Alter Rebbe mentions here specifically a Kirah oven, when it was already explained before in Halacha 8 that by raw meat it is allowed even on a Tanur oven of back then.
 Returning the pot on Shabbos itself, such as intention, covered flame even if food is fully cooked, holding on to pot etc.
 Shabbos Kehalacha Vol. 1 page 379-381
 The Magen Avraham mentions in his 1st opinion that even according to the stringent opinion, if the food is not fully cooked, it may be placed on the fire even close to Shabbos, as in such a case there is no worry a person may come to do so on Shabbos. This follows the ruling of the Tur and Rosh. However in his second opinion he mentions the Smak and Hagahas Maimanis which prohibit even if the food is not fully cooked. Based on the rules of the Codifiers, the Magen Avraham himself holds like this latter opinion, and so is implied also to be the opinion of the Alter Rebbe. It requires further analysis as to the ruling of the Mishneh Berurah.
 Shabbos Kehalacha Vol. 1 page 379
 The reason for this is because on Shabbos one will never come to place food for the 1st time on the fire. Thus there is no reason to be stringent that before Shabbos one may not place food on for the 1st time if there is not enough time to heat it.
 Being that even on Shabbos itself there are opinions which permit one to even initially place food on it. Thus certainly here when the issue discussed is only a stringency there is room to be more lenient.
 Rav Shlomo Zalman Aurbach brought in Shemiras Shabbos Kihilchasa note 185, and Shabbos Kehalacha page 379
 This is usually not the case, as the food is usually cooked enough time before Shabbos to be removed already from the fire and placed down elsewhere until it comes time to place it on the blech