Dishwasher Supply Line - Hot or Cold?

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Chuck B

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I have heard a number of conflicting suggestions on whether to connect a dishwasher to a hot or cold supply line.
Some say connecting to a hotline reduces the need for the dishwasher to heat the water thereby saving energy. I don't see where a dishwasher does it's job with cold water so I'm not certain I understand why others say cold water is better. Please advise thank you!
 

Jadnashua

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Follow the manufacturer's instructions! Every one that I've read calls for it to be a hot supply. I've found it best to run the sink long enough to get things hot before I turn the DW on. That helps, at least with the initial fill. I suppose, if you heat your water with electricity, it may not make a lot of difference, but keep in mind, not all DW are designed to heat the water...some only use the heater during the drying process. If it can heat the water, it also can significantly lengthen the wash cycle if it's coming in cold.
 

Gary Swart

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What in the world would be the sense of this? I do not believe anyone told you the water should be connected to the cold!
 

Joe B

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Here might be one reason why. When the dishwasher is pulling hot water, but it takes a looong time for it to draw _actual_ hot water in the pipes. If it takes a couple gallons of running for the hot water to arrive, one might think, "well, I might as well connect it to the cold water anyway."

Another is for tankless water heater folks. If the dishwasher pulls hot water in an inconsistent way, causing the tankless heater to short cycle or whatever, and it takes a while for the hot water to arrive, perhaps one "might as well" connect it to the cold inlet.

In other words, if the hot line is delivering cold water to the dishwasher anyway, one might as well connect it to the cold. (?)
 

Pseudonym

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I know this is an old thread, but relevant. I am currently looking into a cold water supply dishwasher, for some reasons Joe B stated above...

I not only have a tankless, but it is at the opposite end of the house from the dishwasher. The current dishwasher is meant to be hooked up to approx 120F hot water line (our tankless is set to 140F), but there is no way the tankless will ever deliver even warm water by the time the dishwasher is done filling. So we waste a lot of time AND a lot of water (am in California where water is scarce due to drought) bringing hot water to the sink not only for the first fill, but for EVERY fill in the cycle.

I had read that Bosch can use cold water line. I called, and while that is true it is not recommended for any loads except lightly soiled dishes. According to Bosch, the dishwasher cannot reach full performance from cold.

I also read Miele dishwashers can use cold. I currently have email out to Miele, to see to see what they say.

One alternative is to hire an electrician to wire a new dedicated circuit for an instant hot water tank (or tankless) under the kitchen sink. I'd rather not go this route, I have experience with doing this, it seems they often develop leaks and frequently need replaced every 3-5 years with hard water (mine is moderately hard). I'm retired and am trying to have less maintenance to perform in my home, not more, so would rather not go this route if I don't have to. But it's not practical to keep wasting water and time to deal with a dishwasher that needs a hot line hookup.

If anyone can recommend any other dishwashers besides Bosch and Miele that are known to perform well with cold water supply, please let me know so I can look into those. Thank you.
 

GReynolds929

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Do you not use hot water to rinse the dishes? That way by the time the dishwasher is loaded the hot water is right there ready for use. You could also recirculate the hot water.
 

Reach4

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If anyone can recommend any other dishwashers besides Bosch and Miele that are known to perform well with cold water supply, please let me know so I can look into those. Thank you.
I was under the impression that most machines had a setting to heat the water hotter than comes in. My experience with dishwashers is limited, but mine has such a button-selectable setting. Maybe you have to select that each time.
 

Pseudonym

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I was under the impression that most machines had a setting to heat the water hotter than comes in. My experience with dishwashers is limited, but mine has such a button-selectable setting. Maybe you have to select that each time.
Most modern dishwasher models can heat the water but they'll not reach top performance temperatures. They're fine for everyday dishes but manufacturer does not recommend them for heavily soiled or greasy loads as they can't reach those temperatures.

Our current dishwasher is same. It even has steam cycle for sanitize and uses steam to dry. And a button for a 160F rinse. But it does not heat the water to 140F-180F for the top performance cycles which is what we need. It gets 45F cold water up to about 100F, which just doesn't do well. Yes it does the 160F rinse but we want that during wash cycles too. That's why we run the hot water to it at every drain/refill, then it performs perfectly.

I heard back from Miele. They have several models that use cold water supply. They sent me four #'s in particular that they advertise as top performers starting with cold water.

If there are any other brands and models which are advertised to perform fully using cold water supply, that anyone here knows of, please let me know and I'll look into them. Thank you.
 

Joe B

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For what it's worth, we have installed a Stiebel Eltron point-of-use heater under the kitchen sink and it has been flawless so far. I chose not to plumb the dishwasher to it, since ours seems to be fine with the cold/lukewarm it gets form the main hot water line. It's a ten-year-old Whirlpool.
 

Pseudonym

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I've looked at four Miele models so far that are all recommended to hook up to cold water supply. Unless there is a situation that would require heated water - the reasons they gave don't apply to my situation. Before settling on one of the Miele's, I'm still looking for other brands that will give top performance from cold water, if anyone can recommend.
 

Bannerman

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Dishwasher detergent typically requires 140F to dissolve and for best performance.

Most dishes are soiled with grease/oil or other food residues that will be best emulsified and flushed away using hot water.

Although we are normally satisfied with the performance of our DW, we do find we must increase the water temperature substantially above the usual recommended 120F otherwise, DW performance is not satisfactory.

We've been considering a tankless WH to permit the water temperature to be normally set to 120F, but also allowing the water temp to be temporarily increased at the start of each DW cycle.

Alternately, also considering a thermostatic mixing valve to supply 120F to household fixtures, but with an additional separate hot water line feeding only the DW, to supply higher temperature water directly from the WH.
 

Pseudonym

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My tankless is set to 140 all the time. I looked at those controls (one for each bathroom, one for the kitchen) but decided against. Based on my tankless experience, I made the right decision. The biggest issue is the infamous "cold water sandwich" - even if you still have warm water in the line, it is followed by cold every time the tankless cycles off then starts again. (Installing a recirc pump would mitigate some of that, but also add to the operating costs not just installation cost.)
I installed my tankless 12 years ago (a then top of the line Rinnai) and while it is really nice to have unlimited hot water, I wouldn't do it again. If I had put the installation money into an account, minus the cost of a tank WH, I'd still be paying the hot water portion of my gas bill from that fund, and have years to go. And the Rinnai's warranty was up at 10 years. Then there's the time and expense to flush the unit. Here I find it performs best if flushed twice a year, even though I don't have very hard water. (I don't have a water softener.)
The Miele dishwashers I looked at can do top performance temperatures from cold water supply. Of course that also means a long cycle. My current dishwasher takes three hours to do a heavy-soil load, the Miele's I've looked at are same. And with a cold water supply dishwasher I won't have to set a timer and return to the sink each time I need to bring hot water.
 
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