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Connecting Dishwasher to hot supply

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  • 20-04-2019 5:22pm
    #1
    Ferg2211
    Registered Users Posts: 11 ✭


    I’m looking for a new dishwasher at the moment and have seen some that advertise benefit of connecting to hot water if economical to do so, which it would be for me.
    However my plumber has said you should only ever connect a dishwasher to the main supply, only use potable water.
    Is it safe for health to use a hot water supply for dishwashing?


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    #2
    The Red Ace
    Registered Users Posts: 1,366 ✭✭✭The Red Ace


    Dishwashers should be connected to a mains cold water supply, they work best when connected that way as they wash at a rising temperature. when connected to a hot supply they rarely have enough pressure to fill and often gum up the resin container in the machine


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    #3
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    The Red Ace wrote: »
    Dishwashers should be connected to a mains cold water supply, they work best when connected that way as they wash at a rising temperature. when connected to a hot supply they rarely have enough pressure to fill and often gum up the resin container in the machine

    My hot water pressure is much better than my mains pressure. Its one of the reasons (as well as energy saving) I’m considering this. My question is about the health issues - I was told not to use non-potable water for washing dishes.


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    #4
    Ultimate Seduction
    Closed Accounts Posts: 4,464 ✭✭✭Ultimate Seduction


    Ferg2211 wrote: »
    My hot water pressure is much better than my mains pressure. Its one of the reasons (as well as energy saving) I’m considering this. My question is about the health issues - I was told not to use non-potable water for washing dishes.

    How do people with no dishwasher do it, hardly with the cold tap!


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    #5
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Ultimate Seduction wrote: »
    How do people with no dishwasher do it, hardly with the cold tap!

    With boiled water from the kettle


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    #6
    Car99
    Registered Users Posts: 2,530 ✭✭✭Car99


    Our dishwasher is connected to hot water supply for 10 years now and it washes the dishes satis.

    Our dishwasher is designed for connection to hot or cold as long as hot water temp is below 60 degrees C. The manufacturers SMEG in our case specified that.

    Ask your dushwasher manufacturer.


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    #7
    Ultimate Seduction
    Closed Accounts Posts: 4,464 ✭✭✭Ultimate Seduction


    Ferg2211 wrote: »
    With boiled water from the kettle

    No! You put on the emersion for half hour.

    What is the point of having a hot tap in the kitchen sink for???


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    #8
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Car99 wrote: »
    Our dishwasher is connected to hot water supply for 10 years now and it washes the dishes satis.

    Our dishwasher is designed for connection to hot or cold as long as hot water temp is below 60 degrees C. The manufacturers SMEG in our case specified that.

    Ask your dushwasher manufacturer.

    Yeah there’s lots of dishwashers out there designed for max 60 degC. My hot water is never more than 45 so all good there

    However, this is what my plumber wrote and I’m trying to find out if he’s wrong or right:

    “a dishwasher must be connected to the mains cold supply into your house, it cannot be connected to either hot or cold water that is supplied from your tanks. This is a health issue and the water must be what is referred to as potable which means suitable for drinking.”


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    #9
    Ultimate Seduction
    Closed Accounts Posts: 4,464 ✭✭✭Ultimate Seduction


    Ferg2211 wrote: »
    Yeah there’s lots of dishwashers out there designed for max 60 degC. My hot water is never more than 45 so all good there

    However, this is what my plumber wrote and I’m trying to find out if he’s wrong or right:

    “a dishwasher must be connected to the mains cold supply into your house, it cannot be connected to either hot or cold water that is supplied from your tanks. This is a health issue and the water must be what is referred to as potable which means suitable for drinking.”

    He's wrong! People have been washing the dishes with hot water for as long as we have hot water. If you're dishwasher manufacturer says it's ok then it's ok. Not a health issue atall


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    #10
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Ultimate Seduction wrote: »
    No! You put on the emersion for half hour.

    What is the point of having a hot tap in the kitchen sink for???

    I always use the hot water tap too, hasn’t made me sick yet! I’m just trying to figure out if my plumber is right or wrong when he says it’s a health issue


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    #11
    Hurrache
    Registered Users Posts: 10,148 ✭✭✭✭Hurrache


    Ours was connected to the hot supply by the previous owners. It's a pain in the ass as if you put it on in the evening as it obviously uses the water from the tank leaving you with a shortage of water for showers the next mornings if you forget to boost the hot water.


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    #12
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Hurrache wrote: »
    Ours was connected to the hot supply by the previous owners. It's a pain in the ass as if you put it on in the evening as it obviously uses the water from the tank leaving you with a shortage of water for showers the next mornings if you forget to boost the hot water.

    We’ve got a heat pump and underfloor heating etc so there’s always hot water in the tank. I guess the dishwasher only uses about 10l anyway and the tank is 200l


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    #13
    Markcheese
    Registered Users Posts: 8,428 ✭✭✭Markcheese


    One thing to consider though is that most modern dish washers use very little water,
    So if your hot water tank is a distance from the dishwasher the machine could be almost full of cold water before the hot comes in,
    (if the kitchen sink is next to the dishwasher you should be able to run the tap till the hot comes through, then switch on the dishwasher...

    Slava ukraini 🇺🇦



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    #14
    The Red Ace
    Registered Users Posts: 1,366 ✭✭✭The Red Ace


    Ferg2211 wrote: »
    Yeah there’s lots of dishwashers out there designed for max 60 degC. My hot water is never more than 45 so all good there

    However, this is what my plumber wrote and I’m trying to find out if he’s wrong or right:

    “a dishwasher must be connected to the mains cold supply into your house, it cannot be connected to either hot or cold water that is supplied from your tanks. This is a health issue and the water must be what is referred to as potable which means suitable for drinking.”

    op even with the extra info re temp of your hot water supply and greater pressure on hot as against cold do you know if you have enough lbs/bar pressure to enable the d/w to fill. Rarely have I seen hot water pressure greater than mains, but it will work with either hot or cold once filled but not recommended. A rising temp wash is more thorough and also the latest machines have different technology to control them to the machines of a decade ago


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    #15
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    The Red Ace wrote: »
    op even with the extra info re temp of your hot water supply and greater pressure on hot as against cold do you know if you have enough lbs/bar pressure to enable the d/w to fill. Rarely have I seen hot water pressure greater than mains, but it will work with either hot or cold once filled but not recommended. A rising temp wash is more thorough and also the latest machines have different technology to control them to the machines of a decade ago

    The water tank is downstairs so we have a VSD pump and expansion tank that maintains a high pressure and ramps up if more users are using it. The Miele dishwashers for example advertise the hot connection as a design feature potentially saving 50% energy costs.

    My question has always been about the health concern of potentially using contaminated water for the final rinse though, not so much about whether or not the dishwasher or my plumbing were okay to do it...


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    #16
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Markcheese wrote: »
    One thing to consider though is that most modern dish washers use very little water,
    So if your hot water tank is a distance from the dishwasher the machine could be almost full of cold water before the hot comes in,
    (if the kitchen sink is next to the dishwasher you should be able to run the tap till the hot comes through, then switch on the dishwasher...

    Thanks - hadn’t thought of that. Tank is in utility room, next to kitchen so it’s a short run


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    #17
    soram
    Registered Users Posts: 172 ✭✭soram


    I'd be more worried about your standard hot water supply if it is only 45 degrees to be honest. This is too low and will potentially foster Legionella in the system.

    http://www.hse.gov.uk/healthservices/legionella.htm


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    #18
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    soram wrote: »
    I'd be more worried about your standard hot water supply if it is only 45 degrees to be honest. This is too low and will potentially foster Legionella in the system.

    http://www.hse.gov.uk/healthservices/legionella.htm

    It santises at 60 degC once per week. So I wasn’t quite right in saying never more than 45 degC


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    #19
    Sleeper12
    Registered Users Posts: 16,878 ✭✭✭✭Sleeper12


    Ferg2211 wrote: »
    The water tank is downstairs so we have a VSD pump and expansion tank that maintains a high pressure and ramps up if more users are using it. The Miele dishwashers for example advertise the hot connection as a design feature potentially saving 50% energy costs.

    My question has always been about the health concern of potentially using contaminated water for the final rinse though, not so much about whether or not the dishwasher or my plumbing were okay to do it...


    In bold is nonsense unless you have "free" hot water from solar.



    Dishwashers & washing machines with cold only supply are all A, AA or AAA energy rated. They only heat the required amount of hot water. Taking hot water from the cylinder is more expensive & wasteful. If I turn on my hot kitchen tap I will fill 6 or 7 liter jugs of cold water before I get hot water from the tap. Obviously this means I leave the same amount of hot water in the pipes to go cold afterwards. I waste 6 or 7 liters of hot water every time I use the hot tap. It's known as the deadleg. You will have a dead leg going to your dishwasher too. Then the water is too hot & the machine has to add cold water to cool it down wasting more hot water.


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    #20
    Ferg2211
    Registered Users Posts: 11 ✭Ferg2211


    Sleeper12 wrote: »
    In bold is nonsense unless you have "free" hot water from solar.



    Dishwashers & washing machines with cold only supply are all A, AA or AAA energy rated. They only heat the required amount of hot water. Taking hot water from the cylinder is more expensive & wasteful. If I turn on my hot kitchen tap I will fill 6 or 7 liter jugs of cold water before I get hot water from the tap. Obviously this means I leave the same amount of hot water in the pipes to go cold afterwards. I waste 6 or 7 liters of hot water every time I use the hot tap. It's known as the deadleg. You will have a dead leg going to your dishwasher too. Then the water is too hot & the machine has to add cold water to cool it down wasting more hot water.

    Yes have PV Solar and heat pump. Heat pump is 3 times more efficient than normal at heating water so definitely energy savings can be made. Run is short from utility to sink in kitchen.


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