Why Should I Run the Hot Water Before Starting the Dishwasher

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Dear Home Ec 101,

I have always followed my Mom’s advice about running hot water in the kitchen sink before (and while) turning my dishwasher on. She also says that if you run the cold water at any point while your dishwasher is running, the water in your dishwasher will be cold. My husband recently replaced our sink and garbage disposal and noticed that our dishwasher is only hooked up to hot water.

So, do I really need to abide by my Mom’s rules?

Wondering About Water Temps

Heather says

Your mom is partially right. Running the hot water before starting the dishwasher ensures the water that fills the machine is hot instead of lukewarm. You don’t jump in the shower the second you turn on the hot tap, right? It takes a moment for the water that has been cooling in the hot water pipe from the water heater to the tap to be flushed out. Typically your dishwasher is hooked into the hot water line

Remember cleaning is accomplished through several forms of energy:

Thermal – the higher the temperature, the more dirt can go into solution. It should be noted that the heating element / timer combo in your dishwasher was designed to boost hot water near 140°F. If you check your appliance manual or the website of your manufacturer, you’ll see most recommend water at least 120°F but not more than 150°F. (140°F is the recommended setting for most home water heaters.)

Physical – in your dishwasher this is the accomplished with spray

Chemical – this would be your detergent (Oh and as an unasked for aside and plug, I’ve been trying out the Smarty Dish by Method, which was phosphate free before there was the voluntary ban on phosphates and it’s friggin’ awesome. I bought it myself, Method didn’t supply it).

Running the cold water while the machine is running shouldn’t be an issue, but running the hot water before the basin of the dishwasher fills ensures your dishwasher starts with every advantage. Having to rewash dishes is far less efficient than running the hot water before starting your machine. You can always catch the water in a bucket and use it (when cool, naturally) for other tasks like plant watering, if water conservation is a big concern.

Send your reader questions to helpme@home-ec101.com.


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28 thoughts on “Why Should I Run the Hot Water Before Starting the Dishwasher”

  1. A question on your aside: what were you using before Smarty Dish? We have been using Cascade for a long time, now in the power packs, but I am curious if the Method detergent works better.
    BTW, I purchased the Method lavender All-Purpose cleaner on your recommendation, and I love it! It smells so good, and cleans better than the Fantastic that I had been using.

    •  @KimClemmer I was using Finish, the brand that used to be called Electrasol. For a long time I stuck with Cascade, but the reformulation was leaving a gritty film on my dishes.
      Electrasol was better, but not fabulous, I tried the Smarty Dish on a whim, have used it for about 10ish loads so far and I’m happy. 

      • @HeatherSolos @KimClemmer I just tried the Smarty Dish last night and it worked great. I have really hard water and this is the first time my knives and plastic came out perfectly clean (yes I always use a rinse aid too).

    •  @phobos512 many have a booster, yes. The booster is designed to take water from 120ish to usually 140F. 
      GE recommends checking to ensure your hot water heater is getting 120F to your dishwasher by measuring the temperature of the water at your faucet
      If an average faucet uses 2 – 2.5 gallons a minute (3 if it’s not water saving) and dishwashers use about 6 gallons of water a cycle. If it takes 1 minute for your water to get hot, that’s 1/3 of the water that has to be brought up to temp. 

        •  @HeatherSolos Sorry… messed up posting comment. Heather’s right, most heaters in dishwashers are designed to boost or maintain hot water temps NOT bring water from Tepid up to Washing Temp. There are a couple of VERY simple to install hot water re-circulation systems on the market now (I highly recommend the versions by Watts or Grundfos). The one from Watts is actually an OEM version of the Grundfos one, and is available at Home Depot / Lowes and is pretty much a self install. This will keep the water at your kitchen sink warm to hot negating the need to run water… also makes hand washing and manual washing faster / easier. Disclosure: I *used* to work for Grundfos (got laid off during economic down turn), I’d still highly recommend their systems.

      • I did a risky experiment at home. I turned on the dishwasher and it started to fill with water. I siphoned the water out with a hose and poured 2.5 boiling hot water 210 degrees inside it with detergent. I also used a Digital thermometer to measure heat inside. When it started to wash, I saw loads of steam come out. The water temperature dropped immediately and continued to fall as it washed. When it drained, the temperature was 120 degrees. This was only the first wash session of 5. I checked the dishes and they were all clean but slippery. I did 2 rinses with regular hot water and the entire load was spotless. The dishwasher washed 2 full racks of dishes using a total of 3 fill ups. This experiment proved my point of using hot water from the start. It had no harmful effects on the machine. Total time 25 minutes.

  2. I believe most dishwasher has a heater to heat up the water to desired temperature and the timer of the wash cycle would not start until that temperature is reached.
    If you have a gas water heater and by getting water hot before turning on the dishwasher, you are using hot water that was heat up by gas (more energy efficient) rather than electricity from the dishwasher. Even so, most dishwasher still need to use some energy to increase the water temperature because most water heater aren’t set to high enough temperature for dishwasher for safety reasons.
    Having that said, I am not sure how much energy would be saved if your water heater is operated with electricity…

  3. I’ve never heard that, I guess you learn something new every day.

    My dishwasher does not use all the soap, there is always some left in the dispenser even though I use the recommended amount.

  4. Oh my Gosh!  I can’t believe I just found your site, home ec is like my secret closet passion.  I sit and read how-to-clean books from beginning to end.  Can’t wait to read back articles and follow.  Thanks!

  5. Okay so I have a couple of interesting things to share regarding my HE dishwasher.  I recently had a technician come to maintenance it.  The tech explained to me that the newer HE models use a very small amount of water and the little packs that say “ultra’ or “extra” or “super” or “add big adjective here” should not be used along with the rinse aids.  He said the newer dishwashers don’t have enough water to dilute the chemicals and he had actually seen dishes with the actual GLAZE removed due to the chemical cocktail.  He also said I need to wash it with vegetable oil.  (Yea, I know…sounds weird…but it really did work.)  He poured about 1/3 cup vegetable oil on the door of the dishwasher and ran the longest and hottest cycle.  He said the vinegar I had been using wasn’t doing a thing.  After the visit and cleaning my dishwasher finally produced clean glasses.  Of course, none of this is in the owners manual.
    Also ~ I started making my own dishwasher powder with Epsom Salt, Borax, Super Washing Soda and Lemi Shine.  I am pleased with the clean results of the dishes.  However, I have got to figure out how to keep it from clumping together.  I may just “go with the flow” and make tablespoon sized cubes somehow.  Oh, and, yes, you only need ONE TABLESPOON of the home made powder.  Two main ingredients are the same as laundry soap, I all ready have tons of epsom salts so I only had to buy the Lemi Shine.  It was in the dishwasher area in a plastic canister similar to baby-snack cans.
    So……….those are my dishwasher discoveries to date.  I hope it helps someone out there!

  6. I have had a dishwasher for years, and moved from the UK  to the Middle East.  I took the dishwasher with me 😉 and hoped that the system was compatible with the machine.  In most of the eco-friendly machines (outside the US, as far as I know) it seems to work out less expensive when it is the machine heating its own water.  Machines in the UK are cold-fill, and rapidly heat water.  Perhaps it is something to do with the central hot water heating systems?  
    They recently proved that it was more economical to use a (cold fill) dishwasher in the UK to deal with a day’s load of washing-up, than to fill the sink with hot water from the tap.  In the UK, the gas boilers control the central heating system and also regulate the hot water temperatures.  Some machines only use about 10 litres of water and it seems pointless to have to heat the water in order for the dishwasher to do its work.
    What do other people think?

    • I agree with some of your statement but using hot water from the hot water tank is more energy efficient because it’s 240 volts. A dishwasher is not. For example, a portable space heater uses more power to heat up a room then the furnace. The furnace is 220/240 volts. The space heater is not. Newer dishwasher use less water than you can wash AND rinse by hand. If the dishwasher starts with cold water, it will be using more power in the long run.

    • That is 100% absurd and ridiculous. In every cooking or culinary they always emphasize it is imperial that warm to hot water be used in washing dishes to kill bacteria not to mention it cuts through grease and grime far more efficiently.

    • This is where most of us have it wrong. It’s more energy efficient to start with hot water. The heating element in a dishwasher is used to heat water up further than the water tank. If you start off with cold water, the cycles take longer to run due to heat-up time. Cold water does nothing for a dishwasher to clean dishes.

    • Dishwashers are designed to heat warm water to the ideal washing temperature. Your home water heater is likely -depending on its age, of course- more efficient.

      Can a dishwasher heat cold water to washing temperature? Yes.
      Is it the most energy efficient way? Not necessarily. And depending on the model the heater may be on a timer not a thermostat.

      Is this a life or death situation? No. Less than ideal? Depending on the model, quite possibly.

      • I realize this post is two years old, but it’s still ranked pretty high on some water heater related Google results, so I’d just like to point out that this particular statement is flat out false:

        “Your home water heater is likely -depending on its age, of course- more efficient.”

        Given that the vast majority of water heaters today are still the standard electrical type, the energy required for a brand new standard electric water heater is exactly the same as the energy required for your dishwasher to heat the same amount of water. Electrical heating elements are by definition 100% efficient, all of the electricity used is converted to heat.

        Therefore if you have a standard electrical water heater, there is no efficiency difference, period, in heating the water. However, let’s consider what we’re being asked to do here:

        Run the water for a few minutes to bring the hot water to the dishwasher… As you’ve indicated, each minute you run the hot water you waste up to 3 gallons of water per minute. Not only is that water itself wasted, but that’s now 3 gallons of water your water heater has to re-heat that wasn’t even used to wash any dishes.

        Furthermore, that water has to run through pipes from the water heater tank to the dishwasher. I’ve seen depressingly few homes where these pipes are insulated, so much of that energy used to heat the water is simple dissipated through the pipes on it’s way to the dishwasher.

        So, given that each gallon of water requires the same electrical energy to be heated regardless of whether it’s heated in your water heater or the dishwasher, does it make more sense to heat 12 gallons by running the hot water tap for 2 minutes where much of that heat is lost in the pipes (Where it’ll require re-heating by the dishwasher anyway) or to simply let the dishwasher heat only the 6 gallons it needs at the point of use so you don’t need to worry about transmission losses from pumping the water from one place to another?

        If you’re one of the very few households that have a solar or heat pump based water heater, obviously those ARE more energy efficient than the electrical elements in your dishwasher. Natural gas or propane may also be more efficient/economical. But most houses today still use regular old electrical heating elements to heat water, and those have been 100% efficient for as long as they have existed. Heat pump water heaters are more than 100% efficient because they don’t heat the water by “generating” heat, they do it by moving heat from the air around the tank into the tank. Those are very expensive and not all that common yet.

        Gas water heaters obviously aren’t 100% efficient, as much of the heat goes out the exhaust. However the real efficiency loss for electric heating is in the transmission losses getting that electricity to your home. Instead of burning natural gas at an electrical generating station, sending it through dozens of step up and step down transformers and over hundreds of miles of electrical wiring and then convert that electricity to heat at your home, a gas water heater turns the fuel into heat right in your tank, which overall is usually more efficient and cheaper.

        The bottom line is if you’re using electric heating elements to heat water, the one in your dishwasher is just as 100% efficient at doing that as the one in your water heater, and heating it in the dishwasher eliminates the need to pump that water through pipes to get to the dishwasher where much of that heat would be lost, in addition to negating the need to waste water trying to get hot water to your tap.

    • You mom must have a portable dishwasher to turn on cold water from the faucet because no under the counter dishwasher is hooked up to a cold water line. All dishwasher in the United States use hot water only. This is different in other countries.

  7. I’ll have to try Smartydish. I too used Cascade until the formulation changed and not use Finish. (Why the name change from Electrosol??) Finish is ok but occasionally I have to rewash something. Probably because I stuff the dishwasher to get it all done. I like how Smartydish is made by Method and is better for the environment and probably for humans too!

  8. Hi Heather, I just came across your article when I was looking for an answer to the hot water pipe purge question. I can’t quite make sense of this sentence:

    “If an average faucet uses 2 – 2.5 gallons a minute (3 if it’s not water saving) and dishwashers use about 6 gallons of water a cycle. If it takes 1 minute for your water to get hot, that’s 1/3 of the water that has to be brought up to temp.”

    Are you saying that, “If an average faucet uses 2-2.5 gpm (3 if it’s not water saving), and dishwashers use about 6 gallons per cycle, and it takes 1 minute for your water to get hot, then 1/3 of the water used in the wash cycle has to be brought up to temp”?

    Thank you for any clarification you can provide on the way the dishwasher heating element works during the cycle. I’m uncertain as to how much standing water there is in the washer during the cycle.

    • When a dishwasher is running, it will circulate the water as soon as gravity can make it fall. It holds just enough water so the pump doesn’t pull in air. About 2.5 liters of water will circulate throughout the dishwashers chamber. A older KitchenAid dishwasher could pump 55 gallons per minute (gpm) while using 14 gallons of water per wash load. Today’s dishwasher use 5-7 gallons total. Now that a dishwasher can heat water by itself, it won’t use as much from your water tank. This new feature took place in the “90”.

  9. I got a question. It appears that at the end of the cycle the water in the dishwasher is cold. How I know this is I turn on the hot water at the sink and it is cold. Maybe this is why my dishes are not getting clean. Is there always an element in dishwashers that act like instant hot water and compensates for the cold water coming in?

    • Yes, your dishwasher has a heating element. However, the temperature at your sink at the end of the dishwasher’s cycle doesn’t matter. It’s already done its job. The hot water at the beginning of the cycle is what matters the most. You want the hot water to help with the most with the food particles that need to be brought into solution. The heating element will be quite hot when the rinse water is pumped in.


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