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Cost of heating two cylinders

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  • 18-05-2021 12:21pm
    #1
    stillatit
    Registered Users Posts: 28 ✭


    I have two hot water cylinders in my home installed by the previous owner. The one upstairs services most of the house perfectly. The 2nd one is downstairs in a hot press in the utility room. It provides water only to an ensuite bathroom overhead. It is handy for airing clothes but seems excessive and must be expensive. I use the water for shaving and washing hands, but not much else.


    Does anyone know a way of calculating the cost of heating that 2nd tank?

    Various plumbers have given me hugely varying estimates or anything from €20 to €500 per year.

    If the 2nd cylinder were decommissioned, another way of getting hot water to the ensuite would have to be found. It could be a considerable expense, but I need to know what the current system is costing me before investigating the alternatives.


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    #2
    Calahonda52
    Registered Users Posts: 12,235 ✭✭✭✭Calahonda52


    what size is it?
    how is it heated?
    how often is it heated?
    https://www.electricireland.ie/residential/help/efficiency/energy-efficient-water-heating

    “I can’t pay my staff or mortgage with instagram likes”.



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    #3
    stillatit
    Registered Users Posts: 28 ✭stillatit


    what size is it? - I don't know what is the standard size
    how is it heated? - Gas
    how often is it heated? - Morning (2.5 hrs ) and Evening (2 hrs or more depending on weather

    Not much water gets drawn from it.


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    #4
    Sleeper12
    Registered Users Posts: 16,919 ✭✭✭✭Sleeper12


    stillatit wrote:
    what size is it? - I don't know what is the standard size how is it heated? - Gas how often is it heated? - Morning (2.5 hrs ) and Evening (2 hrs or more depending on weather

    An hour is usually enough to heat up a full cylinder by gas. Hopefully you have valves linked to cylinder thermostats so it shuts off when cylinder has reached temperature.

    You can save a small fortune by turning off the valve on the cylinder that doesn't use much water & not heat it with gas. It will be far cheaper to use the electric element for 30 to 60 minutes once a day.


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    #5
    Calahonda52
    Registered Users Posts: 12,235 ✭✭✭✭Calahonda52


    How well insulated is it?

    “I can’t pay my staff or mortgage with instagram likes”.



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    #6
    Bigdig69
    Registered Users Posts: 68 ✭✭Bigdig69


    Calahonda52 wrote: »
    How well insulated is it?

    It is factory insulated. Though about 25 years old.


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    #7
    Bigdig69
    Registered Users Posts: 68 ✭✭Bigdig69


    Sleeper12 wrote: »
    An hour is usually enough to heat up a full cylinder by gas. Hopefully you have valves linked to cylinder thermostats so it shuts off when cylinder has reached temperature.

    You can save a small fortune by turning off the valve on the cylinder that doesn't use much water & not heat it with gas. It will be far cheaper to use the electric element for 30 to 60 minutes once a day.


    How accurate is this when electricity costs much more per KWH?


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    #8
    Sleeper12
    Registered Users Posts: 16,919 ✭✭✭✭Sleeper12


    Bigdig69 wrote: »
    How accurate is this when electricity costs much more per KWH?




    From what you said you have gas on twice a day heating water. That's fine for the main cylinder but not for the one that gets little use. For washing hands & shaving you only need to heat the top part of the cylinder. Your set up has the cylinder full of hot water 24/7. If you heated your cylinder with element & timer on SINK this will be much cheaper than heating a full cylinder with gas.



    Even one cylinder in a home but only using top part of cylinder is usually cheaper to head with electric immersion. Immersion is 100 percent efficient. Gas isn't. The further away your gas boiler is from the cylinder the less efficient it is at heating the water. Even the super efficient condensing boilers aren't efficient when fired up first. You have to run them awhile before the condensing starts. General rule of thumb: Top part of the cylinder is cheaper with electric & full cylinder cheaper with gas.



    Might be worth having a plumber walk around the house & they can advise better. Your set up seems to tread both cylinders the same even though you need far less hot water from one of them. Maybe a motorized valve on the east used one (if there isn't one already) linked to a cylinder stat might make heating both by gas more efficient


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    #9
    [Deleted User]
    Posts: 17,728 ✭✭✭✭ [Deleted User]


    stillatit wrote: »
    ....................


    Does anyone know a way of calculating the cost of heating that 2nd tank?

    Various plumbers have given me hugely varying estimates or anything from €20 to €500 per year...................
    stillatit wrote: »
    ...............
    how is it heated? - Gas
    how often is it heated? - Morning (2.5 hrs ) and Evening (2 hrs or more depending on weather.................

    Ok, so how much is your gas bill annually?
    Once you subtract the standing fees etc you'll see the cost of the gas you use.

    Probably 20% ish is for this tank presuming you don't heat rads 4 hours/day May to September.


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    #10
    Lenar3556
    Registered Users Posts: 1,359 ✭✭✭Lenar3556


    If they were newer cylinders with minimal loss and thermostats, I would say leave them on all the time.

    The loss from newer cylinders is so small that it’s really not worth messing with sink immersions etc. and not having hot water when you need it.


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    #11
    Lenar3556
    Registered Users Posts: 1,359 ✭✭✭Lenar3556


    Bigdig69 wrote: »
    How accurate is this when electricity costs much more per KWH?

    It all comes down to rate of loss from the cylinder. If it’s poorly insulated, with big losses then it will be costing quite a bit to keep it hot. Albeit the losses are primarily back into the house as space heating.

    But with modern well insulated cylinders the cost of keeping it hot all the time is quite small. Electricity vs Gas...there might not be as much in it as you might think. Particularly if the hot water demand in the house is low.


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