Many homes and buildings are heated using a hot water radiant heating. (Water is heated in a boiler in another room. It flows through pipes in the building to the radiator where much of the heat is given off; then the water returns via pipes to the boiler.)

Suppose one set a pan of food directly on a radiator, which is quite warm to the touch but would not burn your skin. What is the status of that food in regard to bishul? Is the dish a kli rishon? Is the radiator considered a heat source? Would it be prohibited to place a dish on a radiator on Shabbos?

  • Since the hot water is inside the radiator, perhaps it is like putting the dish on a blech or on the top of a tea urn. Apr 8, 2014 at 3:27
  • Can you comfortably rest your hand on the radiator when it has been on for a while?
    – Tatpurusha
    Apr 8, 2014 at 5:36
  • I discussed this problem with my LOR with respect to putting wet towels on the heated "towel rail" on Shabbos. He said he would not do it because there was a possibility of heating the water in the towel above yad soledes bo. Apr 8, 2014 at 13:39
  • 1
    @AvrohomYitzchok, clothes have separate issues anyway; see Shulchan Aruch 301 (somewhere around s'if 40 or so?).
    – msh210
    Apr 8, 2014 at 14:45

1 Answer 1


It really depends.

Was the dish cooked before? If it was, and is a dry food, or is a liquidy food and is still warm (This is the Rema's opinion, the Mechaber requires it to be yad soledes), there is no problem of cooking on a biblical level. If it's a cool liquid, there may be a biblical prohibition (See chazon ish who assumes that Rema concedes that this is only a rabbinic prohibition...).

If there is no biblical problem, the only possible issur is chazarah, a rabbinic prohibition. This issur does not apply to places where one does not normally cook (See OC 253:5), such as on a radiator. Therefore, where it is halachically called previously cooked, it is permissible.

If it was not cooked, or is a liquid which has cooled off, then the biblical prohibition of cooking applies, provided that it will be heated to Yad Soledes Bo. If it will not be, then it is permissible (OC 318:14). The definition of yad soledes in terms of degrees is the matter of much debate (on which I'm sure you can find a lot of literature online), which I don't really want to go into....

If one already cooked the food in a prohibited manner, the food may be prohibited to consume. This depends on if the prohibition is unanimous (MB 318:2).

As always, be sure to ask your LOR. I apologize if not everything is sourced. All of the stuff on biblical cooking can be found pretty easily in Siman 318, and on chazarah in Siman 253).

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