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julie94062

Is hot water needed for dishwasher, or does it heat cold water?

julie94062
13 years ago

I have a 40 gallon water heater in a closet in my kitchen which only supplies water to the kitchen area (there is another water heater for the bathrooms, laundry). In doing my kitchen remodel, we are considering a few different options...tankless in the same location, tankless in a different location, smaller tank, etc.

I hadn't thought of it, but recently read something about dishwahers heating water and was wondering...is there a hot water line to the dishwasher, or does it heat cold water??

If it heats cold water, my hot water needs are obviously much less and that would affect my decision :-)

Anyone know? Thanks!

Comments (30)

  • davidandkasie
    13 years ago

    most use hot water, though some higher end models can heat cold. check teh manual for your DW, but honestly i would plan on being able to supply it with hot.

  • dadoes
    13 years ago

    Many units that can heat cold water are still recommended by the manufacturer for connection to a hot water supply, generally for consumer convenience in not having extended cycle lengths due to the heating time. In some cases the only way to know is by checking service documentation, technical manuals, or just being familiar in detail with how a particular dishwasher works.

    The user instruction manual can sometimes tell the story, if it outlines specific target temperatures for the various cycles. In some cases it may advise, in regards to a "sanitizing" cycle for example, that the unit may not necessarily reach the target, which means the machine can heat but only within allowed time limits.

    One that I know for sure can work with cold water is the Fisher & Paykel DishDrawer. Some Miele units can, and probably Bosch.

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  • julie94062
    Original Author
    13 years ago

    Thank you both for your replies. I'll look into the dishwashers mentioned and check the manuals.

    Thanks!

  • brickeyee
    13 years ago

    "If it heats cold water, my hot water needs are obviously much less and that would affect my decision"

    A DW only uses a small amount of hot water when it is actually filling (a couple times per cycle).

    If you limit hot water use at the sink when the DW is running you could size the instant unit for the larger of the two.

  • dadoes
    13 years ago

    A DW only uses a small amount of hot water when it is actually filling (a couple times per cycle).Dishwashers fill more than for just one wash and one rinse per load of dishes. Typically four to six water changes depending on the selected cycle. Some of the newer HE models may get by with three on a light cycle. My DishDrawer does 7 water changes on the heaviest cycle (approx 0.8 gal per fill).

  • davidro1
    13 years ago

    factoids

    Someone answering the phone at Miele told me last year that connecting their dishwashers to cold water was good for the Crystal wash cycle, as that wash option needs lukewarm water, not hot hot water. However, he said he advised mixing both cold and hot (combining the pipes, mixer) so that incoming water was neither too hot nor too cold, but just right.

    Depending on your house plumbing, some hot water pipes give too hot water.
    Depending on your cold water temperature (in winter it can be very very cold in some places), the temperature of your cold water pipe input can be SO cold that the dishwasher has to heat it a long time. He didn't say whether their DW had a timer that prevented the heating process from continuing a long time when incoming water was very cold.

    Now, I didn't get a Miele, and I don't have to wash much Crystal any more.

    So, I'm considering using IHW and cold mixed together. Both hot and cold, combined into one input... This would then help provide enough water of this just right (warm-hot or hot-warm) temperature setting, to not drain the entire IHW tank and to not push the DW heater to its limit.

    In the long term I could foresee kitchen product manufacturers calibrating Instant Hot IHW with dishwashers' needs so that they can sell a more integrated suite of products. And then homeowners and remodelers wouldn't need to concern themselves with the Hot water tank far away near their shower. It might even become unnecessary to have a hot water line from that big tank to the kitchen.

    HTH
    -david

  • brickeyee
    13 years ago

    "My DishDrawer does 7 water changes on the heaviest cycle (approx 0.8 gal per fill)."

    Sounds like a reason to stay away from them.
    Maybe they omitted the filter.

  • jakethewonderdog
    13 years ago

    All dishwashers have a heating element that will help to maintain the temp of the water - some of the more expensive ones will actually pause and boost the temp of the water since hot water is critical for proper performance.

    For those that do boost the temp of the water, they usually take considerable extra time to do that. And as folks have pointed out, they fill multiple times.

    Most dishwashers state that water temp is important for proper cleaning - that they require at 120 degree water (I think they used to say 130, but scalding was a problem)

    In general practice, I've never heard of connecting a dishwasher to anything but hot water.

    I have heard that very hot water combined with harsh dish soaps have caused etching on crystal. I think that can be eliminated by reducing the amount of soap and using the Crystal setting.

  • heimert
    13 years ago

    My DishDrawer does 7 water changes on the heaviest cycle (approx 0.8 gal per fill).

    Even with that much, that's a very low burden on a hot water heater--that's about as much hot water as you'd use to wash your hands (that is, each .8 gal).

    Put it this way--whatever you get for a dishwasher will not need a huge hot water heater.

  • dadoes
    13 years ago

    BrickEyeE,

    About a year and a half ago I used a Kill-a-Watt meter to check my DishDrawer's power consumption. I set my household tankless water heater at 70°F to insure the dishwasher received a "tap cold" fill and had to heat the water fully to the target temps.

    0.4 KWH - Normal cycle with Eco modifier - 4 water changes (3.2 gal), 125°F main wash and final rinse.

    0.58 KWH - Normal cycle (non-Eco) - 5 water changes (4.0 gal), 140°F main wash, 150°F final rinse.

    0.68 KWH - Heavy cycle (non-Eco) - 7 water changes (5.6 gal), 150°F main wash, 163°F final rinse.

    I don't know what is the current national average cost-per-KWH for electric power, but taking $0.15/KWH as an example and not including municipal water/sewer costs:
    - Normal Eco - $0.06
    - Normal non-Eco - $0.087
    - Heavy - $0.102

  • jakethewonderdog
    13 years ago

    Hey Dadoes:

    I ran the numbers and mine match up exactly with yours. That is, how much electricity does it take to heat 0.8 gal 50 degrees * 7 fills * cost of electricity.

    So if you are running the DW 5 times a week you pay about 2.00 per month in electricity to run it. Not bad.

    Your mileage may vary.

  • asolo
    13 years ago

    Every DW manual I've ever read says to run the water hot at the associated tap before turning DW on. Huge water waste to begin with. At my place, that's 2 1/2 gallons down the drain before serious hot water even begins to come out. And that original fill drops by 40 degrees or more within moments of beginning circulation over the surfaces of the ambient-temp dishes in the machine.

    Then there are the drains/refills....after the water in the hot water line has cooled waaaay down again. That's what the machine gets for fills for all of the rest of the cycles. Basically, the whole thing is a joke unless the machine can, in fact, heat its own water.

    There are a few machines that hook up to 220vac and heat their own water efficiently. The rest of them -- like my two Whirlpool Gold 1500's -- just do what they can with 110. Both of these machines wash very well. They both take two hours or more to do it.

  • dadoes
    13 years ago

    Jake, not all the wash or rinse periods are heated to a target temp. The element may be on, but only the main wash and final rinse are extended as needed to reach the target. I rarely run the machine 5 times per week. Usually can get by with two or three loads.

    asolo, my DishDrawer instruction manual does not advise the sink tap is to be run before starting. The troubleshooting section for cleaning problems and such does not reference running the tap as a potential solution. It does say that the initial displayed cycle times are estimated based on 120°F incoming water and that cooler water will result in longer times.

  • jake2007
    13 years ago

    Dadoes,

    I just did the math on the electricity needed for water heating... It didn't include the motor and such. That's probably why it came out the same.

    Asolo,

    Dude, you should really insulate your hot water pipes.
    Part of the reason that the dishwashers go through a couple of rinses at the start - in addition to getting the a lot of the food off -- is to get the water hot and start heating the dishes so that by the time it gets to the wash cycle, everything is hot. If your pipes aren't insulated and it's a long run, you may have significant heat loss.

    Also, 110v and 220v are equally efficient at heating water. It's just that the 220v will do it faster given the same current draw.

    The bottom line remains that the less expensive dishwashers have a heating element that helps to maintain water temp. These may have more fill cycles in order to get the water and dishes hot.

    The more expensive ones can actually pause the cycle to bring the water up to proper temp. Since temp is critical to proper cleaning, this can be very helpful and can save water if you don't have to run the water at the sink.

    In any case, you connect the dishwasher to the hot water line unless your manual says not to.

  • homebound
    13 years ago

    A little off topic, but has anyone done the comparative figures for just washing them in the sink the old fashioned way and using a dish rack, rather than using a dishwasher?

    I find dishwashers annoying (wait for it to be filled before running, bending over too many times, applying some sort of load strategy that others in the house will disagree with, wet cup bottoms afterward, etc. I prefer wash and get them done in the sink.

    Just wondering if I'm the only one out there.

  • jake2007
    13 years ago

    Homebound:

    Let me answer you by taking a moment, on behalf of all males living alone, to praise the inventor of the dishwasher... aka the place to store dirty dishes other than the oven.

    Dishwashers have vastly improved the sanitation habits and mate attracting abilities for thousands of men who would otherwise be denied an opportunity for lasting companionship because of the condition of their kitchen.

  • davidro1
    13 years ago

    if you are really frugal with water and soap you might outdo a modern dishwasher. Otherwise they win in terms of efficiency.

  • homebound
    13 years ago

    Jake,

    You obliterated my argument with one fell swing. I forgot to consider that - a major oversight!

  • lordliverpool
    7 years ago

    I can also confirm that the best thing about a dishwasher is storage of dirty dishes. I don't mean that I'm in the habit of leaving filthy plates around for days. If I handwash dishes I leave them to soak for a while first. Dishes pile up quickly and clog the sink, getting in the way of what I'm doing. This is common when preparing a complicated meal: you pile the dirty dishes and utensils in the sink and then find they're in the way when you want to fill up a pan with water or whatever. Many can be washed up as you go, but then they pile up on the draining board or rack, and you have to play a game of Tetris to fit them all in. The dishwasher is a Dirty Dish Storage Unit with added washing feature.

  • lordliverpool
    7 years ago

    As far as hot water vs cold water, there doesn't seem to be one clear answer. One thing some people are confused about is if connecting the dishwasher to cold water means it will wash with cold water: no, it's doesn't. The only question is how the water is heated.
    If your gas boiler is efficient, it will cost less (and use less energy) to heat one litre of water than your dishwasher, all things being equal. But the boiler will take time to heat the water, so if the dishwasher waits for the hot water to come through, will it waste lots of water? Some here are suggesting not - it uses the cold water for rinsing, just as it does if it's heating the water with its heating element, which is faster but not instantaneous. If this is true, running the hot water tap before turning on the dishwasher makes no sense at all. Another consideration is the temperature. My boiler is set to 50 degrees C, but the dishwasher has programmes that run at 35-45 degrees. Which uses less energy, the boiler serving water at 50, or the dishwasher heating to 35-45 using the element? I'd still guess the boiler, but I'm not sure.
    I think I'll do a test myself and run the numbers.

  • pcakerh
    5 years ago

    Our HWT is remote from kitchen, so takes a long time for hot water to reach DW, but we live in a desert area and I hate to waste the "hot " water down the drain until it gets hot. Our DW has a heating element but it always seems above the water surface when I open door to check, so how could it safely heat the water? Also, there seems no preheat option on panel. DW is a Whirlpool Gold about 15 yrs old, I am guessing.

  • Robert Booth
    4 years ago

    by using a hot water heater booster made by Case Acme and a 4 port manifold installed between the booster hot water inlet and my tankless hot water heater (intellihot iq250) I am able to have dedicated lines of very hot water (175 degrees, WARNING: WATER THIS HOT CAN CAUSE IMMEDIATE 2ND AND 3RD DEGREE BURNS)) to my dishwasher and washing machine. No need to use the "heated wash" button or the "heated dry" button. It has taken a while to get used to not pre-washing the dishes before loading them into the DW. Just a quick rinse to remove the bigger bits.

  • Robert Booth
    4 years ago

    pcakerh: consider installing a hot water recirculation pump. If you can do basic plumbing it is a do-it-yourself projects.

  • Gary DeRoy
    4 years ago

    To answer the question, it most likely heats cold water. I have a $300 Frigidaire DW (also sold under several brand names) that's about as cheap as they come and it has a heating element.

  • HU-729666554
    3 years ago

    To Robert Booth: can you provide more details on the water heater booster and manifold for dedicated very hot linecto dishwasher? It sounds like what I’ve been thinking of doing, and I would like to benefit from your experience. How can we discuss this offline?

  • HU-770454900
    last year

    Dishwashers are hooked to your hot water line. The same line as your hot line feeding your kitchen sink. The hottest water legally in your house is 120°. Dishwashers have a heating element to get the water hotter to make sure your dishes are properly cleaned.

  • johnson
    last year

    you’re either referring to the law (in Washington State, anyway) regarding rental properties, or you live in some place that has uber nanny legislators. And seriously? YOU don’t think YOU are smart enough to know what temperature YOU want YOUR hot water in your home? Any who, I don’t want the dishwasher to turn the electrical heating element on. Electricity (unless your using magnetic induction) is an inefficient way to heat water. It is better for my house to use hot water from my tankless HWH. I have a tankless HWH that will produce 190° hot water if I set it correctly. I have a dedicated line from the manifold that natal led between the heater and the Case Acme temperature regulator. I send 160° water to my dishwasher, and washing machine. (I also have a dedicated line that supplies 160° to a separate faucet on my sink that takes the place of the under sink contraption that crapped out a while back. (120° is the legal limit? Don’t tell InSinkerator. I doubt those gadgets they make can even go down to 120°.) I would use 180° water but I am afraid the water temperature alone might melt some plastic ware and also damage some synthetic fabrics.


    Here’s a thought, when it comes to how YOU choose to live in YOUR house, man up, and grow a pair.

  • dadoes
    last year

    The enzymes in dishwasher detergents nowadays are formulated to work at lower water temperatures during the wash period, at least initially to deal with some types of soils such as egg/protein residue. The machine heats the wash as it progresses. The final rinse is heated to a higher temperature than the wash, particularly on machines that use the condensation drying method which relies on residual heat of the dishware to promote evaporation.

    Water inlet valves on washers & dishwasher involve plastic parts. The installation instructions for my washer warn that the hot supply is not to exceed 149°F or damage to the water valve may occur.

  • jd Svo
    2 months ago

    There is a ton of misinformation out there- some of it propagated by manufacturers like Miele. FYI: The U.S. electricity grid is only about 17% renewable, so not "green" by most people's standards. Gas water heating is much more efficient than electric, so heating in a common tank water heater is preferred to letting the DW do it all with electricity from a cold water hookup. BUT, if your water heater is a long pipe run from your DW that will tend to even the advantage. BUT, if you regularly use hot water in the sink adjacent to the DW as part of clean-up routine, you have already heated up that long pipe run and the hot water hookup is preferred again. If your heater is close to to kitchen, hot water hookup always preferred. UNLESS you have a huge solar array and battery storage for your house, in which case let the DW do the heating off your green energy source. Clear as mud, right? And yes, I am an engineer.