Why Should I Run the Hot Water Before Starting the Dishwasher

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.



  1. KimClemmer says

    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.

    • HeatherSolos says

       @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. 

      • bookchick says

        @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).

    • HeatherSolos says

       @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. 

        • jdmitch says

           @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.

  2. says

    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. bookchick says

    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. says

    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. deneicer1 says

    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. Fiona says

    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?

    • Mr anderson says

      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.

    • says

      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.

  7. says

    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!

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