Chapter 7: Laws relating to electrical appliances

Chapter 7: Laws relating to electrical appliances [1]

1. Ovens-Opening and closing an oven on Shabbos?[2]

In previous times, when coal ovens were in use, there were various restrictions associated with opening and closing the oven on Shabbos due to that opening and closing it could cause the coals to further ignite.[3] While this issue is no longer relevant today in our gas and electric ovens, nonetheless, there is an additional issue relevant to modern day thermostat-based ovens, which is the change of temperature that the opening and closing of the oven can cause. For example, if the thermostat is set to maintain a heat of 250°F in the oven, then opening the oven can cause it to quickly lose this temperature, and cause it to turn on. It is due to this that many ovens today are sold with a Shabbos mode, and contain a Rabbinical certification vis a vis their Shabbos use. What the Shabbos mode does is that it abolishes the thermostat-based setting on the oven, and rather has it turn on periodically irrelevant of the temperature inside, and irrelevant as to how long the oven was left open for. Nonetheless, below we will deal with the halachic status of a thermostat-based oven which does not a Shabbos mode, or if the mode was not activated before Shabbos:

The law of a thermostat-based oven:[4] It is only permitted to open a thermostat-based oven when the oven is currently on, or one left the door partially open from before Shabbos[5] in a way that cold air can enter it, and thus by further opening the oven he is not causing a new action. However, if the flame is not currently on and the door of the oven is closed, then it is forbidden to open it.[6]

The law by all ovens if the food is not fully cooked:[7] It is always forbidden to close the door of an oven that is on if the food inside of it is not fully cooked. This applies by all ovens, whether thermostat-based or with a Shabbos mode.

2. Electric urns-May an electric water urn be used for Shabbos?

The water is heated based on a thermostat: Some Poskim[8] rule a thermostat based electric water urn may not be used on Shabbos as the amount of water that is in the pot effects when the heat will turn on and off. It is thus forbidden to remove water from it on Shabbos [even when the heat is on, as nevertheless this will cause the heat to turn off earlier than expected, and certainly when it is off, as this will cause it to turn on[9]]. Other Poskim[10] however rule it is permitted to be used.[11] 

Shabbos mode-The water is not heated based on thermostat: A non-thermostat based electric water urn may be used on Shabbos. Such an urn is commonly known as a Shabbos mode urn, which is an urn that has a Shabbos mode option that makes the heat turn on periodically, and not based on temperature.

Heating the water before Shabbos:[12] In all cases[13], the water in the electric urn must be heated to half its heat [i.e. to at least 50 Celsius/122 Fahrenheit[14]] before Shabbos [sunset[15]] begins, and hence one must make sure to set it up and turn it on with enough time before sunset for it to heat up to this amount.

An urn which has its valve on its bottom in a way that it is possible to remove all the water from inside:[16] It is forbidden to use a water urn that contains a bottom valve through which one can us to completely empty the urn of water[17] unless a) The urn simply insulates the heat of the water and does not further heat it [i.e. Shabbos mode]; b) There is a transparent measuring area which tells one how much water is left in the urn; c) The valve is slightly above the bottom of the water. Nevertheless, in all cases one is to beware not to remove all the water from the urn, as this can cause damage to the urn, or causes the safety feature to shut off the heating element.[18]

May urns with a transparent water level measurer be used on Shabbos?[19] Some Poskim[20] rule one must block water from entering the water level tube.[21] Other Poskim[22] rule it is permitted to be used on Shabbos.[23]

3. Air-conditions: May one open or close the windows of his house if this will cause the air conditioner or heater to turn on or off earlier than expected?[24]  

Yes.[25] This applies even if there is a difital temperature reader that will be affected by one’s opening of the door.[26] However, a Baal Nefesh should make sure that a single window is always left open.[27]

4. Fridge:

A. May one open the door of his fridge if it will cause the motor to turn on or last longer?[28]

This matter is disputed amongst the Poskim. Practically it is best to only open the fridge while the motor is on. While the motor is off, one should be stringent against doing so being that it will cause the motor to turn on sooner.[29] The scrupulous are stringent to attach a timer to the fridge and only open it while it is off, on the timer. This thus prevents any problem of starting up or continuing the motor.[30]

Asking a child to open the fridge: Many are accustomed to allowing a child to open the fridge when the fridge is off.[31] However some Poskim[32] have ruled against even having a child do so.

Shabbos Fridges: Today there are special Shabbos fridge settings that come with fridges which effect that on Shabbos the fridge does not work on temperature basis but on time basis. Such a fridge which had its Shabbos setting turned on before Shabbos may be opened even when the fridge is off.

Important note by modern-day fridges: The classic discussion in the Poskim regarding refrigerators was limited simply to the idea of it causing the fridge to turn on sooner. However, in truth, by today’s modern-day fridges there are many more issues at hand, including electronic sensors that are activated as soon as one opens the fridge for the sake of feeding information to the fridge’s motherboard, to help with its advanced technological function. This issue was never discussed by the above said Poskim, and hence in light of the new development, it is practically a necessity for one who purchases a fridge today to purchase one that contains a Shabbos mode, or other possible Shabbos integration so it can be used on Shabbos without any transgression.

B. May one open or close the door of a fridge if the light was left active?

It is forbidden to open or close the door of the fridge if the fridge light was left active, and will inevitably turn on or off upon being opened or closed. This applies even if all one’s Shabbos food is in the fridge. Thus, if one opened the fridge and then realized the light was left on, it is forbidden to close it.[33]

A gentile: It is permitted to ask a gentile to open the door of the fridge even if the fridge light was left active and will inevitably turn on upon being opened.[34] This applies even if one will benefit from the light turning on.[35] This applies even if one can make do without opening the fridge and the matter is not a great need.[36] Some Poskim[37] write that it is best not to tell the gentile about the light, and rather to simply ask him to open it. It is likewise permitted to ask the gentile to close the door.[38] In order to be able to open the fridge the remainder of Shabbos without needing to ask the gentile each time to open and close it, one can either: a) One may hint to the gentile to remove or deactivate the light bulb.[39] [Some Poskim[40] rule one may even ask him directly to remove the bulb, if one needs to continuously open and close the fridge for the sake of one’s Shabbos food.[41] According to Admur, however, it is forbidden to directly tell him to remove it and it may only be done through a hint.[42]] or b) One is to leave the fridge door slightly open through placing a towel and the like in-between, and thus leave the light constantly on.[43]

A child: It is forbidden to ask a child to open the fridge even if the child is beneath the age of Chinuch and even if he is a mere infant.[44] Some Poskim[45], however, permit telling the child to remove the plug from the outlet while the fridge is off. This, however, only applies to old fridges which do not have any electricity working when the motor is off. It is however permitted to place a child that is below the age of Chinuch [less than 3 years old] in front of the door of the fridge [without telling him to open it][46], and if the child opens it on his own accord one may leave the fridge slightly ajar throughout the remainder of Shabbos.

5. Water machines and faucets:

A. May one use a water machine that does not have a Shabbos mode?[47]

It may only be used when the motor is anyways on.

Hot water machine: May never use even when the motor is on due to the cooking prohibition.


B. Opening faucets that cause a Melacha to happen:

Opening water affects the digital meter:[48] The allowance of using such a faucet on Shabbos requires further analysis. Practically, while there are sides to permit it, those who are scrupulous try to change the water meter to a non-digital one, and hence circumvent the issue.[49]

Opening faucet turns on pump: If opening the faucet causes an electric pump to turn on, then it is forbidden to open the faucet on Shabbos. Hence, prior to moving into a high riser building, care must be taken To verify this matter and as to how the pump system works.

6. Hearing aids-May one use a hearing aid on Shabbos?[50]

Although some Poskim have questioned its permissibility due to the changes of electric current caused by the voice volume that enters into it, practically, the widespread custom is to permit its use as rule the vast majority of today’s Poskim.

7. Electric plate-Plata Shabbat:

A. May one on Erev Shabbos place food on his electric plate which is not yet on but will later turn on with the timer?

See Chapter 5 Halacha 8B.

B. May one on Shabbos itself initially place food on his electric plate which is not yet on but will turn on latter with the timer?

See Chapter 5 Halacha 8C.

8. Timers-May one adjust the timer of a Shabbos clock on Shabbos?[51]

Some Poskim[52] rule it is permitted to delay the change of whatever is the current status of the timer.[53] Thus if the electricity is now on it is permitted to adjust it that it turn off at a later time than originally set for. Similarly if it is now off it is permitted to adjust it that it turn on at a later time then originally set for. It is however absolutely forbidden to cause the change of action to occur sooner than was set for, whether to have it turn off earlier or turn on earlier. Other Poskim[54] however rule it is always forbidden to adjust a Shabbos clock on Shabbos.[55]

Yom Tov: This matter requires further analysis.

9. Heaters-May one adjust the temperature of a heater?[56]

While the heater is off it is permitted to adjust the temperature to have it be heated to a lower temperature than it was originally set for.[57] [Likewise it is permitted to lower the set temperature for when the heater will turn on[58] while the heater is off.[59]] While the heater is on it is completely forbidden to lower the temperature to have it heated to a lower temperature than it was originally set for. To higher the temperature is not to be done at all, even while the heater is on, by gas/water run heaters.[60] However by electric heaters, the heater may be adjusted to reach a higher temperature [however not for it to turn on at an even higher temperature of the house].

10. Humidifiers-May one add water to a humidifier or vaporizer on Shabbos?[61]

Some Poskim[62] rule it is forbidden to add water to any vaporizer or humidifier.[63] Other Poskim[64] rule it is permitted to add water to a vaporizer if certain conditions are met.[65] The following is the law of cold and hot humidifiers according to these Poskim that are lenient:

Cold humidifier: If the humidifier expels only cold air according to this opinion it is permitted to add water to it if the following conditions are met: 1. The machine is still on and will not turn on due to the added water. 2. No lights in the machine will turn on or off due to the added water. 3. The lights in the house will not decrease their quality of light due to this.[66] 4. One may not remove any part of the humidifier in order to enter the water if doing so causes the humidifier to shut off until the part is reinserted.[67]

Hot humidifier: If the humidifier expels hot air it is forbidden to add water to it on Shabbos due to the cooking prohibition. However, it is permitted to add hot water directly from an urn into the humidifier, fulfilling all the Chazara conditions[68], and provided that all the above mentioned conditions [of a cold humidifier] are fulfilled. Likewise, this may only be done if the water that remains in the container is already cooked.[69]

11. Air cooler-May one add water to an air cooler on Shabbos?[70]

This has the same ruling as a cold humidifier mentioned above.[71]


[1] See Piskeiy Teshuvos 277:6

[2] See Shabbos Kehalacha Vol. 1 p. 239; SSH”K 1:17; Piskeiy Teshuvos 253:8

[3] See Admur 259:7 regarding opening a coal oven: “In a case that one knows there are fiery coals in the oven, then it is forbidden to open it through a Jew, being that [this will cause] the wind to enter it and light up the coals. Now, even though one has no intention to light them up, nevertheless [it is forbidden to open the oven] as [by opening the oven] it is inevitable [for the coals not to light up in the wind]. Nevertheless, it is permitted to do so through a gentile, being that any prohibition which occurs inevitably [when a permitted action is done], does not carry with it a prohibition to tell a gentile to do so for him, as was explained in 253 [Halacha 10].”

See Admur 259:7 regarding closing a coal oven: “Similarly, if one wants to return and close the oven with a sheet of wood, then if it has fiery coals inside it, it is forbidden to close it through a Jew, as the wind blows through a small crack [that is in the area that has been closed]. This is similar to blowing [on the coals] as it lights up the coals even more so then if the oven had been left open. However, through a gentile this is permitted [to be done]. It is even permitted for a Jew to close it as long as he does not close it completely, and as long as he leaves much of it open. However, if he [only] leaves it a little bit open, then certainly the wind will blow inside it and is forbidden to be done.”

[4] Rav Wosner in Siach Torah 2:18; Beir Moshe 4:32; Mishneh Halachos 5:46; SSH”K 1:17; Shabbos Kehalacha Vol. 1 p. 239; Piskeiy Teshuvos 253:8

Other opinions: Some Poskim rule leniently to permit opening the oven even in the above scenario, on the basis that it is not definite that the opening of the oven will cause the flame to turn on. [Igros Moshe 4:74]

[5] The source of this ruling [Minchas Yitzchak] is discussing a case that due to this the oven is always left on, and not when the oven is now off.

[6] The reason: This is forbidden as doing so will cause cold air to enter and cause the flame to turn on sooner than expected due to the drop in the temperature of the oven.

[7] Admur 259:7

[8] Minchas Yitzchak 5:91; Orchos Shabbos 2:26; Shabbos Kehalacha ibid

[9] Orchos Shabbos ibid

[10] SSH”K 1:40 [46 new edition] in name of RSZ”A; Maor Hashabbos  1:12 in letter of Rav SZ”A; See Igros Moshe 4:74 Bishul in which a number of Teshuvos rule that it may be used and no mention is made of any prohibition; Piskeiy Teshuvos 254 footnote 45 one who is lenient has upon whom to rely.

[11] The reason: As it is a case of Germa Delo Nicha Lei and is not a full Pesik Reishei. [Rav SZ”A ibid]

[12] Admur 254:14

[13] This refers to all urns that have adjustable modes, or a switch to turn on:off.

[14] Igros Moshe 4:74 Bishul 24; Shabbos Kehalacha Vol. 1 pages 317-319; See Ketzos Hashulchan 71 footnote 1; Piskeiy Teshuvos 254:6

[15] Admur 253:1 “if by the time the night [of Shabbos] begins the dish is still not cooked to the point of Ben Drusaiy.” M”A 253:26; Peri Megadim 253 A”A 26; Rav Akivah Eiger 253; Shabbos Kehalacha Vol. 1 pages 313-314;

[16] SSH”K 1:40; Piskeiy Teshuvos 318:61; See Minchas Yitzchak 3:137; 5:91; 6:21; Az Nidbaru 7:21; Shevet Hakehasi 3:109; 4:108

[17] The reason: This is due to suspicion that the water may completely finish and one may come to add more water in order to prevent the urn from burning up. [See M”B 318:117]

[18] Minchas Yitzchak ibid; Piskeiy Teshuvos ibid

[19] See Piskeiy Teshuvos 318 footnote 254

[20] Rav Moshe Yadler in Maor Hashabbos end of volume 1 and Minchas Yitzchak 10:28 [unlike his ruling in 6:21]; Minchas Yitzchak ibid according to those who hold there is a prohibition of cooking by water that was not boiled before Shabbos; So rules Rav Asher Lemel Cohen; and the Machon for Halachic technology

[21] The reason: The reason for this is because they suspect the water in the tube does not become Yad Soledes and when one releases water from the urn some of that water in the tube consequently enters the urn of hot water and gets cooked. Furthermore, even if it did reach Yad Soledes, some Poskim rule that so long as the water did not reach boiling point it is not fully cooked and retains a cooking prohibition, and hence when one now removes water from the urn it causes the uncooked water to mix in with the cooked water and further cook. [Igleiy Tal in Hashmatos, retracting from his ruling in the “Ofeh” 8; Tehila Ledavid 318:17 and Rav SZ”A in SSH”K 1 footnote 96 leave this matter in question; Sheivet Haleivi 7:42 and Minchas Yitzchak 10:28 lean to be stringent]

[22] Orchos Shabbos 2:30; Minchas Shlomo 34:23; Shalmei Yehuda 53 in name of Rav Elyashiv; Az Nidbaru 9:14; Shevet Hakehasi 4:108; Or Letziyon 2:30-10; See Minchas Yitzchak ibid that it is possible the water reaches Yad Soledes and hence there is no prohibition according to those who rule that Yad Soledes is already considered cooked.

[23] The reason: As the water in the tube certainly reaches above Yad Soledes [Piskeiy Teshuvos ibid says it reaches between 55-70 Celsius] and many Poskim rule that once water has reached Yad Soledes it is considered cooked and no longer has a cooking prohibition to further heat. [Igros Moshe 4:74 based on Admur 318:9; Az Nidbaru 9:14 seemingly retracting his ruling in Bris Olam; Olas Shabbos 318:12; Shevisas Shabbos 18; Iglei Tal Ofeh 8] Alternatively, all the water in the urn and valve get mixed during the boiling process, and hence according to all everything is already pre-cooked and no longer has a cooking prohibition so long as it is still warm. [Orchos Shabbos ibid] Alternatively, it is permitted being it is a Safek Gerama and not Niacha Lei. [Minchas Shlomo]

[24] Minchas Yitzchak 3:24; brought in Piskeiy Teshuvos 326:9

[25] As besides for the possibility that it is a Psik Reisha which is done indirectly [Grama] and one has no benefit, of which may be done on Shabbos, here it is not even a case of a Pseik Reisha being that one does not know upon opening the door if the heat/air is on or off.  [Minchas Yitzchak ibid]

[26] Piskeiy Teshuvos 277 footnote 51

[27] Minchas Yitzchak 3:24-18

[28] See Piskeiy Teshuvos 277; Minchas Yitzchak 2:16; 3:24-14

[29] Nevertheless this itself is not simple that it is forbidden being that possibly a Psik Reisha which is done indirectly and one has no benefit of may be done on Shabbos. See Minchas Yitzchak ibid which discusses the different sides to the matter

[30] Minchas Yitzchak ibid

[31] Beir Moshe 6 Elektri 4; Brought in Piskeiy Teshuvos 320 footnote 20

[32] Az Nidbaru 2:36

[33] Igros Moshe 2:68; Beir Moshe Electri 6:9

[34] Igros Moshe 2:68; Beir Moshe Electri 6:9-10; SSH”K 31:1; Piskeiy Teshuvos 276:15

The reason: As it is permitted to ask a gentile to perform an action which causes a Melacha to occur as a Pesik Reishei. [Admur 253:10 and Kitzur Hilchos Shehiya Vihatmana regarding a gentile moving a pot that is insulated within coals; 259:7 regarding a gentile opening a coal oven; 276:9 regarding gentile carrying candle; 277:5 regarding having a gentile shake a candle off one’s table; 253:28 regarding having him turn on heater and consequently heat food; 331:12 regarding having gentile soak garment in water; So also rule: Michaber 259:7; M”A 253:18; 259:11; 276:10; Hagahos Maimanis 6:20; Maharil 60; Minchas Shabbos 80:109; Tehila Ledavid 336:4; Tiferes Yisrael Kalkeles Shabbos 5:6; Shoel Umeishiv Gimel 3:3; M”B 259:21; 277:15; 337:10; Shaar Hatziyon 255:1; However, see M”B 276:30 and how he is explained in Piskeiy Teshuvos 276:15; See also Bris Olam Amira Lenachri 16 who is stringent by Biblical prohibitions]

Other opinions: Some Poskim question the basis of the validity of this Heter as perhaps the gentile’s action of opening the fridge is in truth not considered a Pesik Reishei after all, but rather a direct act. This means as follows: A Pesik Reishei is when one does an action that unintentionally causes an unrelated second action to occur. If, however one does an action that has dual functions, one of Issur and one of Heter, then one cannot consider it simply a Pesik Reishei when one is doing the action for the purpose of the permitted function, if it will inevitably perform also its forbidden function. This is similar to the switch of a water machine that accomplishes two things when turned on: 1) Turns on the light and 2) Opens the faucet. If one turns on the switch with intent to open the faucet and thus causes the light to turn on, this is not considered a Pesik Reishei but a direct act, being the purpose of the switch is also to turn on the light. [Rav SZ”A in SSH”K ibid and Shulchan Shlomo]

[35] Tehila Ledavid 336:4 based on M”A 253:41 and Admur 253:28 who allows the gentile to place the food near the heater and then turn on the heater; SSH”K 31:1 footnote 1; Poskim in Piskeiy Teshuvos 276:15 footnote 114

Other opinions: Some Poskim rule that is forbidden to ask a gentile to perform a Pesik Reishei action if one receives benefit from the Melacha that is performed [i.e. Nicha Lei]. [Biur Gra end of 253, brought in Shaar Hatziyon 253:4; Piskeiy Teshuvos ibid; See SSH”K ibid]

[36] Igros Moshe ibid

[37] Beir Moshe ibid; See Rav SZ”A ibid

[38] SSH”K ibid

[39] Beir Moshe ibid; SSH”K ibid; See Admur 307:7

[40] Igros Moshe ibid

[41] The reason: As it is permitted to ask a gentile to perform a Melacha in a time of great need. [Igros Moshe ibid; Opinion in Rama 276:2 and in Admur 276:8; 331:7; 340:2; 446:6]

[42] Final ruling of Admur 276:8; 331:7; 340:2; 446:6 in Hagah; Regarding it being a Melacha Sheiyno Tzericha Legufa: See Admur Kuntrus Acharon 275:2; 278:2; 316:17; 328:3; 334:25; 340:2; 610:7; M”A 307:7; Maharshag 2:54; M”B 302:36; Ketzos Hashulchan chapter 138 footnote 5; Piskeiy Teshuvos 307:10; Amirah Lenachri [Yosef] 2 p. 202-205; Regarding the allowance to benefit from him removing the light, see: Admur 305 Kuntrus Achron 1; 307:7; Piskeiy Teshuvos 276:2

[43] Beir Moshe ibid

[44] Admur 343:5; 265:10; Ketzos Hashulchan 147:3; Beir Moshe ibid

[45] Beir Moshe ibid

[46] Admur 340:10; Vetzaruch Iyun from Admur 266:10, and so rules Ketzos Hashulchan 147 footnote 11, that a child even below Chinuch may only be given an object if the adult has no intent for the child to perform the prohibition with that object, while here the entire intent of bringing the child is for him to turn off the light. Hence on what bases is it permitted? Perhaps however one can say that since here one is not placing the item into the hands of the child and is simply placing him near the item, therefore it is more lenient.

[47] Piskeiy Teshuvos 277 footnote 52

[48] See Orchos Shabbos 26:52 footnote 72; Piskeiy Teshuvos 277:6 and footnote 61

[49] Certainly, it is an act of piety to switch to a nondigital water meter which is cleared of any of the above issues, and does not require one to rely on various halachic calculations to form a leniency. Nonetheless, from the letter of the law there is much room to be lenient to continue using the water on Shabbos even if it is attached to a digital water meter, based on the concept of Gerama, Eino Nicha Lei, Safek Pesik Reishei, by an Issur Derabanan. To note, however, that there are various types of digital water meters available in the market which work in different ways, some being more halachically severe than others due to them working in a way which loses some of the halachic justifications used to permit them. If you would like to know if they have a digital water meter, it does not suffice to simply check if the numbers on the meter are digital or mechanical, as many mechanical number meters are still digitally processed, and one is therefore to look up the company brand of the water meter to find out. The vast majority of digital water meters in Israel retain most if not all of the halachic justifications to permit using them, and many of them are under the certification of the Tzomet Institute. There are also Mehadrin water meters available under the certification of Mishmeres Hashabbos, and the Eida Hachareidis which completely turn off any digital processing throughout Shabbos and holidays. These digital water meters are the most Halachically preferred, as they do not rely on any halachic justification and do not perform any Melacha on Shabbos or holidays.

[50] See Har Tzevi 1:173; Shearaim Hametzuyanim Behalacha 80:40; Chelkas Yaakov 2:41; 3:186; Igros Moshe 4:85; Minchas Yitzchak 1:37; 2:17; 112; 3:41; Tzitz Eliezer 6:6; Minchas Shlomo 1:9; Yabia Omer 1:19; SSH”K 34:28; Orchos Rabbeinu 1:146; Nishmas Avraham 301; Piskeiy Teshuvos 277 footnote 39;

[51] Shabbos Kehalacha Vol. 1 p. 253 based on ruling of RSZ”A brought in SSH”K 23 footnote 73; See Piskeiy Teshuvos 277:5

[52] See PT 277 footnote 42; SSH”K 13:25; Eretz Tzevi 1:72; Minchas Yitzchak 2:10; 3:37; Minchas Shlomo 1:13; Tzitz Eliezer 6:5; Yabia Omer 3:18

[53] The reason: As this is similar to closing a door in front of a candle to prevent it from extinguishing [277:1] or igniting. [277:4] Adjusting the clock does not pose a problem of Mukztah as it is considered MM”I which is permitted top be moved “Letzorech Mekomo”. [Piskeiy tehsuovs 277 footnote 46]

[54] Igros Moshe Orach Chayim 4:91; Yoreh Deah 3:47; Az Nidbaru 3:25; 8:32; Beir Moshe Elektri 6:26; Betzeil Hachomah 2:32

However, the Igros Moshe [Orach Chayim 4:91] plainly rules that all adjusting of Shabbos clocks are forbidden, whether to make the light turn on earlier or later. He does not give any reason behind his explanation.

[55] The reason: As it is similar to removing oil or adding oil to a lamp which is forbidden. [265:1] Likewise the clock is Mukztah MMCK. [Piskeiy Teshuvos 277 footnote 46]

[56] Shabbos Kehalacha chapter 6; Piskeiy Teshuvos 326:9; SSH”K 23:20

[57] As by doing so one is causing the heater to last for less time when it is anyways not even yet on.

[58] Meaning one may adjust to have it turn on only later when the house reaches a lower temperature than was set for from before Shabbos.

[59] As one simply delays it from turning on when it was supposed to.

[60] As there is suspicion that this will cause some of the water to get heated to Yad Soledes as opposed to if it was left at its current temperature.

[61] See Shabbos Kehalacha Vol. 1 6:21-22; Piskeiy Teshuvos 318:28; Minchas Yitzchak 7:21; 8:28;

The possible issues involved in adding water to a vaporizer:

  1. Cooking
  2. Zoreh
  3. Nolad
  4. Increasing or decreasing current of electricity [problem of Molid or Kibuiy of the lights which have their current diminished]
  5. Causing light on machine to turn on or off.

[62] Minchas Yitzchak 7:21

[63] The Minchas Yitzchak ibid forbids adding even cooked hot water to a hot vaporizer being that in his opinion this is considered cooking. Likewise, he leans to forbid even cold vaporizers due to Nolad and possibly causing change of current in electricity.

[64] Shabbos Kehalacha Vol. 1 6:21-22; Hilchos Shabbos Zoreh footnote 64 in name of Rav Moshe Feinstien allows doing so for an ill person; Beir Moshe 6:52 allows doing so through a gentile for the sake of an ill person; Shalmei Yehuda 2:14 in name of Rav SZ”A permits doing so for the sake of an ill person.

[65] According to them there is no problem of increasing or decreasing the electricity as what Melacha is there involved in making a greater current of electricity. Likewise, the electric current does not decrees the quality if the lights in the house due to a mere amount of added electricity. If, however adding more water to the machine takes a lot of electricity then even in their opinion it would be forbidden to add more water if it causes the quality of light in the house to diminish. [Shabbos Kehalacha ibid footnote 33]

[66] See previous footnote

[67] Hilchos Shabbos Zoreh footnote 64 in name of Rav Moshe Feinstien and Shalmei Yehuda 2:14 in name of Rav SZ”A permit adding water only through a water hole and do not allow one to remove any parts to enter the water. Vetzaruch Iyun as the logic of this ruling. Seemingly those machines that they referred to would shut off when the water container was removed and hence if removing the container will not shut off the machine then it is allowed to be done. [Shabbos Kehalacha ibid footnote 33]

[68] Thus, one must pour the water directly from an urn without removing it with a utensil. [Shabbos Kehalacha ibid]

[69] Otherwise adding removing it and then reinserting it is considered cooking the water. [Shabbos Kehalacha ibid] Likewise one may not pour from a Keli Rishon on to such water. [Shalmeiu Yehuda ibid; However, see Shabbos Kehalacha ibid Biurim 6]

[70] Piskeiy Teshuvos 318 footnote 85

[71] Piskeiy Teshuvos ibid concludes that he heard from many great Moreh Horaas that they permit adding water to an air cooler on Shabbos.

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