Beitza 32a (2)
1- We began with our Mishnah which discusses the forming an oil lamp from a clump of clay.
Identifying the author of the Mishnah R’ Yosef asserts that R’ Meir is the author of the Mishnah prohibiting the fashioning of an oil lamp on Yom Tov.
2- The second portion of the Mishnah is the ruling against the production of charcoal.
The Gemara explains the necessity for this ruling. Seemingly, the only use for these coals are for gold smiting which is obviously for work prohibited on Yom Tov. So the Gemara says that the Mishnah is referring to coal that is formed for the sake of heating water to bathe. But bathing on Yom Tov with hot water that was cooked on Yom Tov is prohibited.
The Gemara concludes that the coal was produced to create steam. Sitting in a steam bath was at that time permitted. So this is what our Mishnah meant when prohibiting the forming of coal bricks for the purpose of creating steam.
Gemara Shabbos 40a:
מאי עוברי עבירה דא”ר שמעון בן פזי אמר ריב”ל משום בר קפרא בתחלה היו רוחצין בחמין שהוחמו מע”ש התחילו הבלנים להחם בשבת ואומרים מערב שבת הוחמו אסרו את החמין והתירו את הזיעה ועדיין היו רוחצין בחמין ואומרים מזיעין אנחנו אסרו להן את הזיעה והתירו חמי טבריה ועדיין היו רוחצין בחמי האור ואומרים בחמי טבריה רחצנו אסרו להן חמי טבריה והתירו להן את הצונן ראו שאין הדבר עומד להן התירו להן חמי טבריה וזיעה במקומה עומדת
It is clear that heating water on Yom Tov for the purpose of washing one’s entire body is strictly forbidden. We read the text of Tosfos on the bottom of 21b. Such is the Halocho in the Shulchan Aruch 511,2.
3- We moved on to showering on Yom Tov with water that was heated before Yom Tov. Discussed the gas water heaters with a constant burning pilot light that use no electric current at all. If one were to turn off the gas before Yom Tov, so that no new cold water would be heated, would a shower be permitted?
The short of it is as follows:
According to the Sefardim [Rambam, Ran, Beis Yosef +] cooking water to bathe on Tom Tov itself is permitted Min Hatorah. Cooking water to bathe is similar to cooking water for coffee.
The prohibition is only mi’Derabonon גזירה.
Thus, using water that was heated before Yom Tov is permitted as long as it is a private shower and not in a Mikvah or bath house. [To prohibit it would be a גזירה לגזירה].
According to the Ashkenazim [Tosfos, Rosh, Ramo +] cooking water to to bathe on Tom Tov itself is prohibited Min Hatorah. Why? Because cooking water to bathe is not similar to cooking water for coffee since bathing is not שוה לכל נפש . Only the ‘feinshmekers’ do it daily.
What is the Halachah למעשה on showering with water that was heated before Yom Tov?
[Showering in a home that has an ‘instant hot’, tankless water heater or electric water heater is obviously prohibited]
The Alter Rebbe 511,1 states clearly that although the Halocho is like the Sefardim, the Minhog is like the Ashkenazim “and one should not change [this Minhog].
ואף על פ שהעיקר כסברא הראשונה בכל זה מכל מקום כבר נהנו במדינות אלו להחמיר כסברא האחרונה ואין לשנות