Normally, to "kasher" or "kosherize" a metal sink (from non-kosher to kosher, or before Passover), you clean it out well, make sure it's used for nothing hot for 24 hours, then pour boiling water all over it.

At one point I got tired of shlepping kettles from stovetop to sink, and started thinking: what if I just filled the sink with water, and added in an immersion heater till the whole thing bubbled over?

Has anyone tried this? Is it halachically effective? safe? Practical?

  • What a brilliant idea! Have you thought of using a blow-torch using a can of butane gas? Commented Aug 19, 2011 at 13:32
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    @Avrohom Yitzchok, per Rabbi Herschel Welcher's guidance: please don't use a blow-torch unless you're specially trained and really know what you're doing; especially in home kitchens, which can't handle the punishment that industrial kitchens do.
    – Shalom
    Commented Aug 19, 2011 at 13:46
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    Too add to Shalom's (your) comment. Your sink has a seal of silicon or plumbers putty which may or may not become damaged from excessive heat. You countertop in many cases is Formica (i.e. plastic) glued onto a plywood base. Plywood itself is many layers of thin wood glued together. Any one of the aforementioned can warp and or buckle from excessive heat. Blowtorches would be ridiculous to use. The immersion heater is something to ask someone who has experience with.
    – user6591
    Commented Oct 7, 2014 at 18:05

2 Answers 2


You'd have to do something to force the water to cover the side flanges (or rims) of the sink too (such as by dropping in a hot stone), but otherwise I'd think it would be halachically fine - it should be similar to the case of a very large pot, where you can boil the water for hagalah in it (Shulchan Aruch, Orach Chaim 452:6).

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    And if it's fine, then I'd think it's more than fine. After all, hag'ala by boiling water in a thing is generally considered better than by pouring. No?
    – msh210
    Commented Aug 19, 2011 at 13:54
  • @msh210, good point.
    – Alex
    Commented Aug 19, 2011 at 15:08

I know that in Lakewood there is a Gemach that has an assortment of commercial immersion heaters (some duplex, to fit double sinks) for exactly this purpose. They instruct to turn up the thermostat on your hot water heater, fill the sink with the 190 degree water, then place the heating element contraption on top and plug it in, and wait until it starts bubbling. They also supply bricks to heat on the stove, for kashering the drain.

  • any guess what type of heaters they use, and how long they take? (A minute? An hour?)
    – Shalom
    Commented Aug 19, 2011 at 15:47
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    Same thing you use to heat your coffee, but triple the size, with a thick cord. It's mounted on a plexiglass panel. I think it takes about 30-45 minutes, but there are many variables (starting water temp, sink capacity, air flow, ambient temp, heater wattage, etc.)
    – Dave
    Commented Aug 19, 2011 at 16:01
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    Something like this (grainger.com/Grainger/TEMPCO-Immersion-Heater-2VYJ6). It would make sense to wire it with a 10-amp fuse or circuit breaker. Also keep in mind that these elements must be properly submerged at all times when operating, otherwise they can explode.
    – Dave
    Commented Aug 19, 2011 at 18:51

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