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Immersion heater Sink or Bath?

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  • 14-06-2014 10:38am
    #1
    brian ireland
    Closed Accounts Posts: 1,647 ✭✭✭


    I have on of those boost master timers and I was wondering if its better to heat the water on sink only or bath. We normally put it on in the evening on sink for two hours to wash up and take showers.

    Would it be better to have it on bath for one hour or sink for two hours. Or is it six of one and half a dozen of the other!!


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    #2
    Sleeper12
    Registered Users Posts: 17,092 ✭✭✭✭Sleeper12


    brian ireland wrote: »
    I have on of those boost master timers and I was wondering if its better to heat the water on sink only or bath. We normally put it on in the evening on sink for two hours to wash up and take showers.

    Would it be better to have it on bath for one hour or sink for two hours. Or is it six of one and half a dozen of the other!!

    If you have it on bath for an hour you'll have a full tank of hot water. If you have it on sink for 2 hours you'll only have the top half of the cylinder hot.

    Having said that, so long as your thermostat is working ok your element will stop using electricity once the water reaches the correct temperature. So if you left the sink switched on for 4 hours it wouldn't use electricity for 4 hours.


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    #3
    cast_iron
    Registered Users Posts: 2,454 ✭✭✭cast_iron


    Sleeper12 wrote: »
    If you have it on bath for an hour you'll have a full tank of hot water.
    No you won't. It would take maybe 3 or 4 hours to heat the tank fully on bath. Just one hour on bath will probably just give you a lot of warm water.
    If the OP's current setup of 2 hours on sink in the evening is enough, then stick with it. No benefit in just an hour on bath over 2 hours of sink.


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    #4
    Sleeper12
    Registered Users Posts: 17,092 ✭✭✭✭Sleeper12


    cast_iron wrote: »
    No you won't. It would take maybe 3 or 4 hours to heat the tank fully on bath. Just one hour on bath will probably just give you a lot of warm water.
    If the OP's current setup of 2 hours on sink in the evening is enough, then stick with it. No benefit in just an hour on bath over 2 hours of sink.

    Sorry I have to disagree with you but anyone waiting longer than an hour for a full tank of hot water when on bath needs their system looked at. Maybe your element is caked with limescale, maybe your thermostat is set too low or maybe your plumber put in an element too small for your cylinder.

    An hour on bath should give you enough hot water for a bath. Something wrong otherwise.


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    #5
    cast_iron
    Registered Users Posts: 2,454 ✭✭✭cast_iron


    I disagree.

    Take a 120l cylinder at 15 degrees. To heat it fully to 65 degrees in 60 minutes would take aprox 7kW using Q=m.C.deltaT

    That assumes no losses and no draw on the water over that time. A standard bath element is 3kW, meaning at least 2.3 hours to heat with no losses.

    One hour of a 3kW element would give a 21 degree rise by my reckoning, putting the water in a 120l cylinder at 36 degrees, using the same assumptions as above. Luke warm.

    Drawing water while it's heating would be a bit of an issue the way the OP describes how/when they use the water, thereby adding to the length of time.


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    #6
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    cast_iron wrote: »
    I disagree.

    Take a 120l cylinder at 15 degrees. To heat it fully to 65 degrees in 60 minutes would take aprox 7kW using Q=m.C.deltaT

    That assumes no losses and no draw on the water over that time. A standard bath element is 3kW, meaning at least 2.3 hours to heat with no losses.

    One hour of a 3kW element would give a 21 degree rise by my reckoning, putting the water in a 120l cylinder at 36 degrees, using the same assumptions as above. Luke warm.

    Drawing water while it's heating would be a bit of an issue the way the OP describes how/when they use the water, thereby adding to the length of time.
    I'd say your right.

    Although an immersion won't heat the volume of water for the calculated time, because the stat at top of cylinder will reach 65 degrees while the water is cooler the further down you go. In other words, the element won't heat the full volume of water it can heat(top of cylinder to bottom of element), to the set point of the stat.


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    #7
    cast_iron
    Registered Users Posts: 2,454 ✭✭✭cast_iron


    I suppose it would depend on the setup of the particular tank and its set-point. I know my own immersion has the bath element (horizontal)at the bottom of the tank with the sink element half-way up (also horizontal). The bath element can only be set to about 30 degrees to heat the bulk of the cylinder to about the desired set point of 65. It's actually not possible to set a temperature for the water at the top of the cylinder with this setup.


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    #8
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Yea but the average immersion won't spend the duration suggested by calculations, because firstly only a percentage of the volume of the cylinder is heated at all, and secondly, only the water at the stat is at the temperature in the calculation, the rest below being cooler gradually the further down it is.


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