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Hot water heater setting & dishwasher?

Posted by aceh (My Page) on
Wed, May 16, 07 at 8:28

My brand new hot water heater thermostat setting is right in the middle (that big middle mark on the dial). Is this setting ok for use with a household dishwasher or should I adjust the heater to the next highest setting?


Follow-Up Postings:

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RE: Hot water heater setting & dishwasher?

The temperature setting of your water heater is very closely regulated by the plumbing codes.

If all bathtubs and showers are equiped with "Anti-scald" mixing valves both the International Residential Code and the Uniform Plumbing Code will permit the water heater and potable water distribution temperature to be 140degF maximum. If you do not have anti-scald mixing valves the maximum allowable temperature is 125degF. (some local codes limit it to 120degF).

Most water heater gas controls have an index mark on the thermostat dial to indicate 125degF. It may be a Dot, longer line or possibly a different colored line at the 120DegF index. Keep in mind that the setting on the water heater is only a theoretical setting and it may vary slightly from one installation to another depending upon such conditions as the temperature of the incoming water, fuel gas pressure, etc. The best way to check the temperature is to actually measure the water temperature with a thermometer of known accuracy at the closest faucett to the water heater.

Most residential dishwashers have a built in heating element that is primarily used for the drying cycle, however that element is also used as a booster heater to heat the water in the sump and thereby insure the water is at the required temperature for the dishwasher. Some dishwashers have an "Energy Saver" switch which disables the internal heating element during the wash cycle. If you are having problems with the dishwasher that are attributed to water that is not high enough the first step is to make sure the "Energy Saver" switch is turned off.

If your dishwasher requires a water input temperature greater than the code allowed potable water distribution temperatures the solution is to install a small "On Demand" water heater or a 6gal tank type to supply water directly to the dishwasher.


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RE: Hot water heater setting & dishwasher?

At least one of my bathtubs definitely does not have an anti-scald valve, and nobody has knocked on my door to issue a citation when I've run my water heater at 140F!

In regards to dishwashers ... there may be a difference between *recommended* water temperature vs. *required* water temp depending on the capabilities of the machine. Most Euro brands and some high-end domestic US brands have built-in water heating and can work with a COLD water supply, although that makes for a longer cycle so the manufacturer may *recommend* a minimum incoming water temp of 120F to reduce the heating time that's needed.

Historically, the "Energy Saver" switch on a dishwasher is touted as turning off the heating element during the *drying* phase ... it may or may not have an effect on supplemental boosting of water temp during washing & rinsing. Any machine that is advertised as having full-fledged built-in water heating will *always* heat accordingly for washing & rinsing regardless of any energy saver setting for the drying phase.

The difference between a dishwasher that has assured water heating compared to one that only supplements is that the full heating machine will pause the cycle and continue heating until the target temperature is reached regardless of how long it takes. A machine that only has supplemental heating allows a limited time for water heating and will continue the cycle even if the target temperature is not reached.


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RE: Hot water heater setting & dishwasher?

Regardless of your water-heater setting, you WILL want a DW that boosts the heat in wash/rinse cycles. Almost all of them do this. The mass of the dishes takes a huge amount of heat out of the incoming water even if the first drop comes in at 140F. Even then, the water in the lines settles back to lower temps between fills so the incoming water in subsequent fills will be cooler no matter what you do. My Whirlpools boost to 120F for "normal" washing. "Sanitary" boosts to 155 but I never use it. I believe these levels are typical among various machines.

I would suggest setting your water heater at 120-125 and let the DW take care of the rest.

I have the same opinion of the new HE clothes washers. Those should be purchased with on-board heaters, too, for the same reason.


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RE: Hot water heater setting & dishwasher?

This is a gas water heater and the temperature was set at one hash mark past the middle setting I believe by the plumber. I know for sure my kitchen faucet has the anti-scalding feature. The bathtub does not and I'm not sure about the lavatory. FWIW the lavatory faucet is a Price Pfister TREVISO...not sure if the model is 49-DK00 or T49-K00. (Brushed Nickel)


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RE: Hot water heater setting & dishwasher?

We have very hot water, but when I open the dishwasher to add a dish while its running, the water is barely warm. The dishwasher is almost new--a Sears Kenmore Elite. The dishes are always wet and not warm when the cycle is done as well. What's up??


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RE: Hot water heater setting & dishwasher?

Gayle99,

Wow, for a minute there I thought Lazypup was back! Way to revive a 7 year old thread!

So - to answer your question: Either you are losing all your heat in the water line before it gets to the dishwasher or your dishwasher is malfunctioning. There is also third option: It was plumbed into the cold water line....

Usually the dish washer is connected to the hot water line under the kitchen sink (very few connect to the cold). Can you locate that line and feel if it's warm after dishwasher has been running? This should let you know it was connected properly and hot water is making it to the dishwasher. If it's cold, you have a problem.

The dishwasher has a heating element that maintains water temperature and in some cycles will boost the water temp. Despite what some people say, not all dishwashers heat all of the water on every cycle - but it should at least maintain the temperature / boost it some. If this heater isn't working the water will not stay hot. You can check this by using the "heated dry" feature to see if it gets warm in the dishwasher... if it doesn't, the dishwasher heater is malfunctioning.

Let us know what you learn.


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RE: Hot water heater setting & dishwasher?

Gayle99,

You didn't cite the brand/model of the dishwasher. Some new energy-efficient units don't take much water for each fill. The hot water supply line may not be getting purged of standing cold water by the volume of water the dishwasher pulls for a fill if there's some distance between your water heater location and the dishwasher.

Run your kitchen sink faucet until the flow is fully hot before starting the dishwasher.

Also ... the latest (enzyme) detergents are formulated to work at lower water temperatures than in the past regards to energy efficiency ... they function best with longer wash times at temps low as 105°F up to about 127°F.


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RE: Hot water heater setting & dishwasher?

Wouldn't it be fun to read the dishwasher instructions? That may answer some of your questions! If you cant find them in the junk drawer, check the manufacturer's web site. Besides the recommended water temperature, it may explain what heating, if any, the washer does. As we used to say at work: "When all else fails, read the instructions."

As alluded to above it is important to measure the actual temperature at the kitchen faucet. A meat or candy thermometer would do for that. If you don't have one handy, they aren't too expensive. Depending on the plumbing run, the water may lose a lot of heat between the heater and the faucet (normally the washer is next to the faucet).


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