Reply To: Shabbos Seudah – China or Paper

kapusta-

ambush-

The “hot water on Shabbos” question was discussed on another thread, here:

http://www.theyeshivaworld.com/coffeeroom/topic/hot-water-on-shabbos

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|  hot	  ||	|

|  water  ||	|

|  out	  ||	|

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|	 cold	|

|	 water	|

|	  in	|

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Fire

This is a cut-away view of a gas water heater (I left out the chimney, don’t worry about it).

The cold water coming in goes straight to the bottom of the tank via the long pipe, while the hot water exiting leaves from the top of the tank thru the short pipe.

This arangement helps ensure that the hot water is used up first, and that the water is kept hot throughout the tank due to convection.

If the cold water intake is shut off, there will be no pressure forcing the hot water out when a sink faucet’s “hot” tap is turned on.

Furthermore, even if the sink is below the water heater it may not siphon much because of vacuum that will build in the tank as water is drained.

Even if an air valve is opened on the top of the tank (preventing a vacuum from forming) or even if positive air pressure is pumped in, the tank will only drain until the water level reaches the bottom of the “hot water out” pipe – not a whole lot of water.

There is a device (NOT accepted by all poskim) that supposedly can make hot tap water allowable on Shabbos, by keeping the temperature below “yad soledes bo” temperature.