Does Hot Water EVER Make it to the Dishwasher?

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A dishwasher connected to the hot water line…but does hot water EVER make it to the dishwasher?

When you hook up your new dishwasher most times in the United States, manufacturer installation instructions require the water supply to be connected to a hot water supply line.

But why?

• Dishwashers are supposed to use very little water compared to hand washing!
• How hot should your water going into the dishwasher be?
• Does the hot water ever make it to the dishwasher
• How does the water stay hot?

We will address these ideas and more in this post.

Maybe you are like me—I admit to waiting on one last cup before getting the dishwasher started to maximize the load. I want the dishwasher to clean as many items as possible all at once. By doing this, I continually fill the machine until ready to run a cleaning cycle. This does not happen all at once though. I cannot be certain that the last items I pre-rinse before placing in the dishwasher will give my hot water supply line a full, up-to-temp charge before starting a dishwashing cycle.

If you use a delayed start option, to avoid using the dishwasher at a peak usage hour–say, the middle of the afternoon on a hot day when it is more important for electricity to go to the entire neighborhood’s air conditioners–there is a snowball’s chance in hell for hot water to get to your dishwasher.

Really, how do we KNOW that hot water is even reaching a dishwashing machine?

Depending on how efficient the dishwasher is and how long of a distance you have between your water heater and the dishwasher, hot water may NEVER make it to the dishwasher.

Distance from the dishwasher to the water heater.

Newer dishwashers only use between 2 to 4 gallons over the course of a 2 to 3 hour cleaning cycle.

Energy star dishwasher water usage.

For instance, the regular cycle of my 2009 Kenmore Elite dishwasher uses 1.2 gallons at the beginning, 1.1 gallons 10 minutes later, .33 gallons one hour and 12 minutes into the cycle, another .33 gallons at the one hour and 20 minute mark, and another 1.1 gallons in the rinse cycle at one hour and 27 minutes.

Hot water usage in a normal dishwashing cycle of a 2009 Kenmore Elite.

The only hot water that might make it is that first 1.2 gallons—after doing a good hot water rinse.

Amount and time of the first water used in a dishwashing cycle.

The remaining water demanded during a dishwashing cycle will have cooled off on the way to the machine!

A hot or cold water supply line charge might not be a big deal if your plumbing runs through an unconditioned attic in the summer and your dishwasher is in the attic. That does not happen for most … the dishwasher in the attic part that is…

Insulated pipes can help with maintaining operating temperature after use, but insulation cannot keep stagnant water from falling below 120 degrees Fahrenheit when running through cooler spaces. At any other time of the year, if your plumbing runs underground, or your dishwasher is in your kitchen, or not directly attached to a water heater right next to it, the water going into the dishwasher often will not be up to recommended operating temperature from the hot water supply.

I am not hitting that 120 degrees Fahrenheit requirement in the installation instructions.

EVER.

The maximum temperature at my kitchen sink is 110°F (43.33°C) when the storage water heater thermostat is turned to 120°F (48.89°C).

So how is the water for washing dishes getting to operating temperature?

In this case, you are relying on the heating element inside the dishwasher to do all the heavy lifting to bring the water to a decent cleaning temperature. To add insult to injury, the water heater will be running for no good reason other than to put hot water in a line that will just cool off.

You could run the hot water to pre-charge the line, and somehow use the cold water coming out of the hot line to rinse off the next round of dishes already piling up, or capture it to water plants.

Use cold water instead of letting it go down the drain.

However, you have to ask yourself, do you do this every time?

There is also the option of adding a recirculating loop to your plumbing… that will be an extra cost.

The answer might be perhaps, but I’m going to venture that most normal people do not want to run extra water to pre-charge a hot water line nor do they want to add something else under their kitchen sink, either.

If your water heater is set to 120 degrees Fahrenheit, as mine is from the manufacturer, there will be some cooling in the line as it comes out when the new hot water mixes and pushes the cold sitting water down the line.

Hot water pushing cold water out of plumbing.

Then the supply pipe will absorb energy from the hot water.

Plumbing absorbs heat, dropping the temperature of hot water.

Overall temperature stability will lag just because it has to heat up the copper pipe and the cooler dirt around the pipe below the house as it travels to the fixture.

It takes a while to achieve and maintain a constant hot water temperature…this is not an instant process!

For example, I discovered in this past video, my kitchen sink maxes out at 110 degrees after blowing the cold water out of the line for 2 minutes. (link goes to exact timestamp)

I am not sure how long I would have to run hot water to get it higher and keep it there, if that’s even possible. I’m saying that because at some point I’d be using the water faster than it can heat and the cooling forces between me and the water heater may just be too much to ever reach 120 degrees.

Note, this only applies to storage water heaters, and not tankless.

You can compare that to the first 1.2 gallons that comes out in 1 minute and 8 seconds of a dishwashing cycle. That first .87 gallons for 34 seconds was me filling up the brita filter and the follow on 1.9 gallons in 1 minute and 20 seconds was getting a steady reading after watching the temperature gauge go up.

Phyn Plus water monitor measurements of how long and how much was used to get the hot water to the kitchen sink.

So you can see, if I’m not precharging the line, hot water will not make it from the water heater 16 feet away, but I will say due to a leak under the slab, we know the plumbing takes a meandering route past the kitchen entirely only to make it back through the pony wall to the kitchen sink and dishwasher.

Depending on how often you use your dishwasher, and if, indeed, you DO preheat the hot water line to the dishwasher, this could be a big hit in your electricity or gas budget just from running your electric or gas water heater for no good reason.

This was all a very disappointing haphazard discovery. I would have never known this phenomenon existed without Phyn Plus, my water monitor and shutoff system (you can check out what all it does in this review post: Phyn Plus Feature Deep Dive Review)–that is where the measurements you see came from–you learn a whole lot about your own habits and where your water gets used with one of these devices as well as protect your home from leaks.

Phyn Plus sample daily water usage.

For those of you who have followed my progression on the water monitor side of the blog/YouTube channel–this was a mind-blowing finding and a sneak preview just for you. Phyn Plus gives a very clean usage history despite an open plumbing system (IN OTHER WORDS not all water monitor and shutoff systems are alike and you may see some massive differences in the usage logs dependent on the design of the device). Despite having Flo by Moen installed for years, I never knew how my dishwasher worked. So I was pretty excited…and dismayed (not at Phyn) at what I discovered.

Without knowing how often my dishwasher runs and how much water is used, along with my self-imposed leak tests (an in-progress video series comparing different methods of leak detection), and discovering how to battle thermal expansion for better leak discovery, I would have no clue that hot water does not really reach my dishwasher.

This is crazy!

How is it that probably the majority of us washing dishes are washing with cold water?!? Going into the personal side, perhaps that speaks to our digestive system. However, I’m a bit disturbed that the Energy Star system / manufacturers expect the incoming temperature of water to be something that is not achievable in reality.

THIS SEEMS WRONG.

So what can you and I do to solve this problem because hot water is an essential part of any sanitary dishwashing?

You could immediately start handwashing all dishes and use the dishwasher as a drying rack. This might not be the best idea because of the eventual buildup at the bottom of the dishwasher. Moreover, you could cause long-term damage to your dishwasher from a lack of use: seals could dry out, bacterial growth at the bottom of the unit, trapped stagnant water in the drain line loop…

Dishwashers are not intended to be expensive, decorative drying rack boxes!

Another idea is to increase the temperature of the water heater. It’s important to note that you need to make sure you do not raise the temperature to the point someone could get scalded.

Avoid scalding from setting water heater too high.

A better solution is to educate people like you and me and maybe request cold line dishwashers from manufacturers. This way, we are not asking our water heaters to run more often and not potentially voiding the warranty because you want to install your dishwasher on a cold line instead of a hot line.

However, this kind of request goes against the Energy Star rating system, which encourages dishwasher manufacturers to push the energy burden of heating water to water heaters in order to achieve a positive rating.

I have to say I LIKE efficiency and in discovering something is COMPLETELY wasteful, I would like that to change. If you know of a dishwasher that a manufacturer allows their product to be connected on a cold water supply line, please drop a note in the comments.

A dishwasher connected to the cold water line would be efficient…or at least less wasteful AND HONEST about what appliance should be responsible for the job at hand! Yes, that’s sparkle in that photo!

I’ve also included some research and some lively discussions on this topic in the description below.

• Plumbing to Prevent Domestic Hot Water Scalds
• A Lively Discussion on ALL Things Dishwasher Related to Hot Water
• Energy Star Paraphanelia on Dishwashers

One question I still have outstanding is: how much does the heating element at the bottom of the dishwasher heat the water?

If I pre-charge the line with hot water will that shorten the dishwashing cycle because there is some internal water temperature check where the dishwasher stops to heat the water before proceeding to wash? I know the manufacturer states there is something like that happening, but what incoming temperature is the bottom limit before it just continues on the cleaning cycle. That might be a follow on video–let me know in the comments if you are interested.

I reached out to Kenmore and did not have success finding someone with the answer. However, this is not limited to Kenmore–it is across all dishwasher manufacturers who have products “requiring” a connection to a hot water line.

Please share this information if you know of anyone in the market for a new dishwasher so they are better informed on their purchase. The information online on this subject is pretty light and another lively conversation here could perhaps even make some changes in the future, or at least leave us all better educated.