using hot water from tank on shabbos

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    You keep suggesting a lot of googling and you keep changing your reasons… why don’t you just turn off the inlet valve to your hot water heater and see what happens.

    So far, none of your “fargoogeledta” sevaras are logical.

    SO cold water goes in the bottom of a hot water tank? That does not explain how, when seeking equilibrium, water will suddenly defy that law and the laws of gravity.



    Which is it, water pressue or air pressue? I don’t use hot seltzer so I imagine it is water pressure. ROB, you seem to be missing something very essential here. Water pressure means that there is a load of cold water waiting to enter the tank, but can’t because it is full. When I open my hot water valve, hereby releasing some hot water from the tank, that allows in new cold water, which is what pushes out the hot water.

    This is the same pressure that drives my cold water up the pipe. If I shut my cold water in the basement, the remaining water in the pipes will not go up because nothing is pushing it anymore. The same goes for hot water.


    Nisht and haleivi, am not sure whether my response was sent. Neither you or I are heating engineers. Google is a great source for information. Use it!


    ROB: But I am. And I understand how water moves. And I understand that as long as there is nothing to push out the water (maybe steam buildup pressure, from the trapped hot water), nothing, not even wishful thinking, will get the water out. And certainly not to drive it one floor high. I engineered (ran engines) long before Google came into existence.


    ROB, you don’t know what I know but I do know what you don’t.


    froggie, Haleivi and nisht: I know-FOR A FACT- that many people who shut off the cold water valve before shabbos STILL get their hot water from the tank! (see also earlier posters). froggie, this has nothing to do with the cold water pushing the hot water out. Water will try to find its level,based on the source of water from far away- simple physics! talk to a professor of physics or a real engineer- you may get the right answers!



    Last try. OK? I spoke to an engineer (myself). OK? Please. Unless you don’t believe in science (another thread). Kindly. Tune in to this earthly world.

    If you shut off the intake (cold water) NOTHING WILL EXIT – that is your “source of water from far away”. Unless you have air pressure, or hot line pump. Nothing. Again as I wrote earlier, not even wishful thinking will do it. (Maybe with a Shem – if you’re into those things)

    Unless you are talking about a boiler on the same level or higher than the faucet – then of course one will have water equivalent to the level of the faucet.

    Sometimes one may find some hot water still exists, thats a run from higher elevated lines, which will very soon cease. Or if you have a cross linked faucet, and open both, that’s cold water.

    ‘Know what? Why don’t you try it. Shut off (completely, no cheating) your cold intake. Open kitchen faucet (hot). See how long it takes to empty existing hot water from higher elevated lines. Then stand and wish for hot water to come. Wish harder, five minutes. Post results. (turn back on cold water, it could burn or bust if you don’t have proper preventive mechanisms)


    froggie: will consult engineers. In this cold weather, am not going to turn off water for fear of burst pipes.


    Oi vei, the rebbe is silent and the talmidim bicker. ROB, laws of physics are not to be denied, but they work best when you don’t confuse them.

    In a typical tank water heater or in boiler coil, if the inlet is shut, there can be no outfow without drawing a vaccum.

    Water finding its level is a concept in an open system, not in a pressurized, closed system.

    Fixed volume rigid system in which water is heated must have expansion capacity. Hot water heating boilers typically have an expansion tank. A take can only expel what it took in, and these generally have nothing to do with the domestic hot water.

    In a heated tank, the hottest water will accumulate at the top. If the burner or element is off, and cold water enters at the bottom, and stays there until a thermal drift cycle mixes it in to the hot. This can’t be seen and not well predicted and thus not relevant.

    The ONLY WAY to use hot water from a basement tank is to

    A)have the tank below yad soledes and use in a normal manner with the heating element or burner OFF. A limited supply of lukewarm water.

    B) To attach an alternate pressure source, that wont be mevushal, such as air pressure vessel, or air compressor loaded, but shut off. The air entering the tank will drive the hot water out, instead of the cold water (with cold vavle off)

    C) to have a gravity flow system, with the tank above the point of use (Kithcen) and a vaccum relief to let air into the tank as the hot water exits. This does not work too well if the hot outlet of the tank is at the top, as in an American type water heater. IOW, this need to be purpose-built by someone who knows what he/she is doing.

    ROB, are you referring to some European setup?



    twisted- I wrote a long answer which disappeared in the ehter.let’s try again.

    As you write, in england , the hot water tank is in the attic and, when you shut off the cold water intake, the hot water still flows out,as it seeks to level with the source. Same in many apartment buildings, where the water tank is on the roof.

    Our hot water tanks here in our houses usually is in the lower level and maybe the level aspect is notb apparent. However, you can google anything to do with standard hot water tanks and you will see that there are no pistons, no pumps anywhere in sight in the tank. So, if are you saying that,when the cold water source is shut off (and you are right to say that the cold water drfits to the bottom, being heavier), the hot water does not come out of the faucets (taps for you, new yorkers), I am skeptical about this. Methinks that the hot water will continue as it seeks to find its level with the original source.

    BTW- the expansion tank is only tied to the BOILER for the house heating. Our tanks have individual heating, not tied to the boiler.

    As far as your “jad soledes bo”. The fact is that,unless you shut off the thermostat, when the water temperature drops below a certain number, the heating will come on. That, again, may very wlel be a true gromo and not even “psik reisha.”

    In conclusion- I think that hot water will continue to flow when the cold source is shut. You do not.


    ROB, if water has such a good memory, why doesn’t it jump out of my cup to get to the clouds? Yes, it’s true that water, while connected, will go back to the same level it came from. This is based on the gravitational force of the rest of the water bearing down on it.


    Haleivi:yo answed you own question.only in a situation where the waers are connected does this rule apply,not in your cup.


    Typical water heaters in the US are designed not to empty unless the drain valve is opened (or when the tank develops a leak just after the warranty runs out). This is by design to prevent the possibility of heating an empty tank.

    From what I’ve read, in the UK they often use an indirect water heater where there is no burner in the heater. These systems will not be damaged by running dry so they are allowed to empty. If such a system is installed above the living space the pressure from the cold water inlet is not required to deliver hot water.


    And it answers you as well. If you shut off the intake then it is disconnected from its source.

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