I would like to understand what kind of warming drawer is usable on Shabbat. Some warming drawers apparently are sensitive to changes in temperature. For example, if you open the drawer and the heat escapes, it might cause the heating element to work to maintain a set temperature. This is a similar issue with refrigerators or room thermostats. Yet, it is not ones intention by opening the drawer to set off the heating element to on. I am not sure if this is any different than walking to a door where there is a sensor that turn on a light when you approach and therefore permissible. Please advise asap since I need to decide on placing an order for a warming drawer. Thank you.
Thank you for your question. Firstly let me say that I am in no way familiar with the technical workings of any warming drawer, so I can only answer your question in general terms. There are several questions that may arise with a warming drawer, and there are several Rabbinic opinions about their use. The first problem is that perhaps it looks like one is cooking when putting food into the drawer on Shabbat (of course only fully cooked dry food may be heated up on Shabbat in any way). Some Rabbis hold that if the drawer heats to above "yad soledet bo", about 45 degrees, this is a problem. If one follows this opinion, the drawer needs to be set to a low temperature. But many Rabbis hold that even a hotter drawer would be allowed, as one does not ever cook in the drawer, but only uses it for warming, and as such there is no issue of appearing to cook when food is placed in it. The second problem is that perhaps one will adjust the temperature setting on Shabbat. To overcome this problem one needs to cover the "fire". In the time of the Talmud this was achieved by covering the coals with sand, or raking the coals away before Shabbat. How could this be achieved in an electric warming drawer? Some Rabbis say that one needs to cover both the drawer's floor with foil, and tape or cover the temperature setting knob. Others hold that it is enough to tape or cover the knob. The major problem is whether opening the drawer causes one to be doing "melacha" or forbidden labor on Shabbat. If opening the drawer directly turns on (or off) a light, fan, or electrical element, all opinions hold that it is forbidden to open it on Shabbat. (I have heard that some drawers have an automatic safety switch which turns off the element when the drawer is opened, and this would definitely make the drawer's use forbidden). However, if opening the drawer just causes the temperature to drop, and then as a result the element will turn on afterwards (that is - it is not a direct switch which turns the element on, but there is a thermostat that will be affected by the cold air entering the drawer when it is opened, and as a result may turn the heating element on sooner), there is an argument as to its acceptability. Some hold that this is forbidden. But many others hold that this form of very indirect causation, where there is a marked separation between the action (opening the drawer) and the labor (the element turning on) is permitted. This is similar to the argument about opening a refrigerator, which will allow the hot air to enter the fridge and set the thermostat off (though the warming drawer is of a more serious nature as the fridge motor is possibly a Rabbinic labor, while the heating element is a Torah one). I have learnt from my Rabbis to allow the use of a warming drawer on Shabbat if the setting knob is covered, and opening the drawer does not cause a direct labor. One who follows this opinion certainly has Rabbinic sources on whom to rely. Of course one may certainly decide to follow the more strict opinions (see for example the Star-K website). As I wrote above, I cannot advise as to which brands are acceptable or not. Blessings.