Rabbi Baruch Bodenheim: Gemara Shabbos: Third Perek – Monday, Elul 9 – Sugya: Heating food on Shabbos (09/01/25)

One of the bnei Chabura sent this to me

We have finished the Hachzara sugiya, but I still have a few questions on halacha lemaase, would it be possible to cover them?

I would like to discuss a few of these questions this week

1. When the oven is working on Shabbos (the oven is in Shabbos mode and the controls are covered), there is hot air coming out of the exhaust at the back of the oven. Is it allowed to put the food over the exhaust, or the exhaust opening has the status of kira which is not grufa vektuma?

2. What is the minimum depth of the pot which we turn upside down on the blech to put food on it? 

3. Is there a maximum size of the pot which we turn upside down? For example, can it be a commercial baking pan that covers the whole blech?

4. Stam pot without food in it is muktze, correct? If yes, should the pot that will be turned upside down to put food on it be designated before Shabbos, or any pot can be used? 

5. Can food be placed directly on blech far from the fire, where it is not yad soledet bo?

6. Can food be placed directly on blech not over the fire, where it is yad soledet bo?

As well as the questions below 

The prevalent practice is to use a blech on a stovetop which would serve as קטום. What is the source that a sheet of metal would accomplish the same halachic status as placing ash on the coals? 

See שולחן ערוך אורח חיים ס’ רנ”ג סע’ ג and משנה ברורה ס”ק פא

https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=51

In many electrical appliances the heating elements are covered by a sheet of metal like a crock pot which the walls of the crock pot covers the coils. Does one need to cover/line the crock pot or is the sheet of metal/ walls considered a blech? 

Learn רש”י שבת דף לז. “גבה

Learn מגן אברהם שי”ח ס”ק לא

https://hebrewbooks.org/pdfpager.aspx?req=14325&st=&pgnum=26

See ביאור הלכה שי”ח ס’ א “ליתן עליה

https://hebrewbooks.org/pdfpager.aspx?req=60388&st=&pgnum=45

Learn ששכה”ל פרק א סעיף כט & הערה פב (new print)

Learn קובץ הלכות שבת ח”ב פרק כו סע’ יח & הערה כד 

Would aluminum foil which does not reduce the temperature be acceptable to be considered קטום?

Learn קובץ הלכות שבת ח”ב פרק כו סע’ יג & הערה יז-יח 

Learn ששכה”ל פרק א הערה סג (new print)

If one leaves the aluminum foil on the electrical appliance from week to week. Is it still considered קטום ?

Learn קובץ הלכות שבת ח”ב פרק כו סע’ יט & הערה כז 

A hot plate that does not have ability to change its temperature, does it need to be covered?

Learn ששכה”ל פרק א סעיף ל & הערה פג (new print)

Learn אגרות משה או”ח חלק ד ס’ עד בישול ס”ק לה

Learn קובץ הלכות שבת ח”ב פרק כו סע’ כ & הערה כט