Some dishwashers have a hot and cold water intake, but it's pretty rare, abd only makes sense if you heat your water with some alternative energy source. Letting the cold water bleed out makes sti zero sense either way.
this post was submitted on 12 Sep 2026
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Your dishwasher uses hot water so if you run your sink until hot water is coming out before running your dishwasher it means it's immediately getting hot water. It's about clearing the cold water out of your pipe.
Whether or not you can use the sink while the dishes are being washed depends on your water heater. If you can wash your hands while someone is taking a shower without blasting them with cold water then you should be fine to use your sink while the dishes are being washed.
In the US, you need to run hot water before starting the machine, but once the machine is running there is no reason you shouldn't be able to use the sink as normal.
The federal government put restrictions on how much energy a dishwasher can use in a cycle, which has significantly restricted how much time they can spend on heating water and drying the dishes at the end of a cycle. In order for dish detergent to work properly, the water needs to be at least 135ºF, most machines aim to reach 140ºF. Most manufacturers will also state incoming water needs to be 115-120º minimum in order for them to be able to work (which is a common-high setting for a hot water heater - 120ºF is hot enough to scald you if you are not careful). If you do not get the cold water out of the pipes between the hot water heater and the kitchen, then the water starting temperature won't be high enough and the dishwasher won't work as well (specifically the detergent won't work as well).
Not every dishwasher has a heating element. My dishwasher does, and the manual still says to run the hot tap to make the dishwasher more effective.
Also, just because your dishwasher might have a heating element, that doesn't mean you always wanna use it. You know what the "sanitize" setting does if you accidentally leave some oily residue or food on your dishes? Everything gets some junk baked onto it. And then you (actually, me) have to scrub at hard, dried crud that you should have handled before loading the dishwasher the first time, but you were lazy and let your wife wash the dishes, and you didn't know at the time that she doesn't inspect things before baking them in the soapy dish-steamer. (Rant over)
As for washing your hands while the dish washer is running, I've never heard of this issue. Most residential plumbing is capable of carrying somewhere around 6 GPM (Gallons Per Minute), and your faucet is probably limited to 1.5 - 2.2 GPM, but if you wash your hands at that pressure, your shirt is probably gonna be soaked from splashing or spray. Your dishwasher only takes a minute or two, maximum, to fill, and the remaining 3.8 GPM is more than enough. Once your dishwasher fills, the pump (sometimes heated, sometimes not) cycles that water through the jets, and then eventually pumps the water out the drain hose.
If she's upset because you don't like using scalding-hot water to wash your hands, then that's also a non-issue. Your hot water lines are connected to your water heater, and the hot water lines will deliver water from your heater whether you want them to or not. Your cold water and hot water lines shouldn't interact behind the faucet. You can run all the cold water you want at your faucet and the only difference is that not only will the hot water supply line be hot, the cold water supply line will be cold. Separately.
Now, something you shouldn't do is run your disposal at the same time as your dishwasher. When you install your dishwasher, it specifies that you should install a "high loop." This just means to make your dishwasher's drain hose go as high as possible under the cabinet before reaching the sink drain. It doesn't have to be a literal loop, but I like making an actual loop because I like the way it looks. This "high loop" acts as a vacuum break to reduce the chances of your dishwasher sucking dirty water back into it. If you recall how to make a siphon, the two things you need are an unbroken hose with no air pockets to disturb the water flow, and for the source to be higher than the destination. Your dishwasher's drain is at the bottom, close to the floor, and the hose intersects the sink's tail piece around knee-height. The high loop makes it more difficult for backflow water to fill the cavity of the drain hose, so you'd pretty much have to clog your sink drain past the p-trap, and then fill the sink to nearly overflowing for you to move water from the sink drain to the dishwasher. BUT! This isn't true with a disposal. Disposals are capable of generating enough pressure that they can actually push some water up the dishwasher's drain hose. So, if your dishwasher is draining while you use the disposal, and it stops draining while you're still using the disposal, you might actually be able to get some of the ground up food from your disposal past the high loop. Even worse, your disposal can often let through food particles that are bigger than the jet holes in your dishwasher. Since your dishwasher fills and then pumps the water already inside it to spray your dishes, you can end up putting food particles through your pump, breaking it, or through the jets, clogging them. Also, you're taking that dank smell from your disposal and using it to clean your food.
In the United States and other countries with 120V electricity
It has nothing to do with 120v electricity. We used to have dishwashers in the USA that could heat water from cold to 140ºF without issues.
I believe one of the technology connections videos talks about making sure the sink water is hot so the dishwasher can have hot water and not clean with cold water
It might be this video
https://www.youtube.com/watch?v=jHP942Livy0
One thing I just want to point out that's stated in the video is the hot water is for the pre treat cycle. It always heats up the water for the main wash cycle.
came to post this. note: this works if your dw is on same line feed as sink. if for some reason it’s not, you can’t purge the cool water away.
Growing up we had to run the shower until it was hot before we could wash the dishwasher.
https://m.youtube.com/watch?v=jHP942Livy0
Here is a video from someone explaining why you should run the water hot before turning on the dishwasher, along with a few other tips.
Upvote for Technology Connections
Edit: okeedokee I'm wrong.
GE Appliances: Dishwasher - Correct Water Temperature
Ummm...what are all the USA people in here talking about?
I've installed and replaced my own dishwashers 4 or 5 times over the years and helped friends and family members many times. They only last about 5-7 years so it happens often enough for it to be routine for me.
The water supply is connected to the cold water. The dishwasher has it's own heating element. It heats the water to "sanitizing" levels. There's even a sanitize button.
That water gets so hot that I can't open the door mid-cycle with my reading glasses or they'll get completely fogged up.
The sanitize button is not a new development...
They aren't all designed to connect to your cold water line. In fact, most seem to specifically instruct you to connect to your hot water intake. You are right that most in the US have water heaters, but that doesn't mean that the machine's cycles will heat the water effectively for the full duration of the wash.
Maytag, Whirlpool, GE, and LG all recommend you connect to hotwater. Bosch (EDIT: Spelled this like the drug company not the appliance company) recommends cold. Depending on your machines cycles as well, the heating element may not get the water hot enough to make effective use of the pre-wash cycle. If your machine is connected to the hot water line and you purge the cold water from the line, you will see a more effective pre-wash (and thus more effective wash) than if you let it run cold.
North America vs Europe, North America cannot heat the water fast enough due to the limit of being on a 120V and 15 A circuit.
They have 120 volt electricity, it can't heat quickly enough, so the wash cycle will begin with less than optimal temperature and take a while to get to sanitizing temperature.
So they feed it water from the hot water tank, which isn't hot enough usually but the heating element can get it up to temp much faster at 120v.
Many modern dishwashers only have a cold water inlet so it literally does not get water from the hot water tank.
120V really doesn’t matter that much as they are commonly on their own 20A breaker. At 1500W of power it can heat 1.5L of water from 60F to 168F in 1 minute.
Where are you getting your information? Can you find an example of a dishwasher where the installation manual says to use cold water?
And the claim that 120v doesn't matter is baseless.
At 1500W of power it can heat 1.5L of water from 60F to 168F in 1 minute
Lol no it can't, are you nuts? That's physically impossible and mathematically incorrect by a factor of more than 4.
My information is based on installing 3 dishwashers in the US that all said to either connect to cold water or give an option for cold water or hot water
Voltage doesn’t matter for heating what matters is overall power. 1500W at 120V and 1500W at 450V both heat at the same rate. The advantage of higher voltage home systems is they usually allow higher power since current is generally the limiting factor but they make higher current breakers for 120V
I was off on my conversions and did calories instead of joules. Either way it takes 4 minutes to get from 60 to 160 which is still trivial on a multi hour cycle
Here is one that allows either connection but emphasizes increased efficiency with hooking up to cold water. I admitted I was wrong on my conversions will you admit you are wrong that they have to hook up to hot water?
Here is one that allows either connection but emphasizes increased efficiency with hooking up to cold water.
"For fastest possible wash times, with slightly higher energy consumption, connect the dishwasher to a hot water source. Hot water supply specifications: Recommended temperature: 120 °F (49 °C), max 140.
will you admit you are wrong that they have to hook up to hot water?
I never said that.
So weird. You want to be right? Okay, you're right, you don't have to hookup to a hot water, it's recommended and commonly done... I don't think I claimed you have to... The reason it's recommended to hook to hot water is because it's slower at 120v. They all allow you to do whatever the hell you want, but American tap water (which doesn't sit in a rooftop tank that gets warm as it sits around, but that doesn't apply much in the northern hemisphere) is typically not ideal.
You want your dishwasher to take longer? hook it up to cold water and save some electricity, you do you.
1500W at 120V and 1500W at 450V
Why would I use 1500W at 240V? My dishwasher has a 2100W heating element, which heats 40% faster, that's not negligible. You can get higher wattage models.
You installed 3 dishwashers? That doesn't make you an expert on international dishwashers, it just makes you a homeowner. Jesus, you don't have to just argue for the sake of arguing, just say "I learned something dumb today" and move on with your life.
You said "Many modern dishwashers only have a cold water inlet so it literally does not get water from the hot water tank" and then provided an example that says what I said, if you want a faster wash use hot water.
The reason most of the world uses the cold tap for dishwasher hookup is because they use a higher wattage heating element, which they can operate safely because they use 220V power. I didn't come up with the 1500W limit, you did, don't move the goal posts.
You probably have higher voltage and more power going to that heating element, so the cold water line is fine. In the US, the heating elements in our dishwasher can't draw enough power for cold water, so it needs to start with hot water.
Also, 5-7 years is... Pretty bad. It's not uncommon for dishwashers to last multiple decades here. I'm pretty sure mine is at least 20 years old (and ugly lol)
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Not USA but North America and we ours is hooked to hot water. Has to do with having a shitty heating element since they wanted it to be plugged into 120 15A circuit.
I checked under my cabinet just recently, and the dishwasher is indisputably connected to the hot water line.
It was like this in the last place, too, and my sibling’s place.
My sibling’s dishes won’t get clean unless she runs the water first, as her sink takes a crazy amount of time to warm up.
YMMV though. Not all sink piping takes so long to “warm up” anyway.
So test it!
Run a dirty load. If your dishes get clean in the dishwasher, no problem; your routine ain’t broke. If you aren’t satisfied, try running the hot water first.
It’s certainly not worth an argument with an SO though, as it could plausibly help.
It's correct if in a country where the dishwasher lacks its own water heater.
Dishwashers in the U.S don't have water heaters and therefore it's beneficial to purge lukewarm water from the hot water line before starting the dishwasher, such that the water in the dishwasher is on average hotter and as such more effective at washing the dishes.
Dishwashers in Europe have water heaters and as such it's entirely irrelevant to do it there
I live in the US and every dishwasher I ever owned had a heating element, and was capable of heating its own water as needed, depending on what cycle was selected.
Same with my washing machines, my current one even has a steam cycle.
I feel like if dishwashers without heating elements were ever a common thing here, it must have been many decades ago.
Its not so much about that, as it is about the fact that they almost always do an initial "clean-off-the-dirtiest-bits" cycle for around 10 minutes which pulls in (mostly) cold water if your line is not purged like the OP describes. And they don't use the heating element for this initial cycle.
After the first 10 minutes they flush out the super dirty water with the dirtiest food bits and sauce and whatnot, fill in brand new water, and then run for the duration of the washing cycle (1hr plus) along with the heating element.
So flushing the cold water out of your kitchen water lines AND adding pre-wash detergent (such as some extra powder right in the door, outside of the main closable detergent compartment) helps a ton with this initial 10ish minute cycle.
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So do dishwashers in North America they are just less powerful because of the 120 volt.
Dishwashers in the U.S don't have water heaters
Crazy. Mine only takes in cold water. Never even knew ones that take in hot water existed.
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The technology connections guy says it helps assuming your dishwasher water connection is at the sink and that the heating element in your washer isn't very good or efficient.
Detergent packs are kinda wishy-washy (Dishwashers Explained)
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The Technology Connections guy on YouTube thinks so
He also said that with modern detergents, you should do colder washes anyway, as the hot water has little benefit.
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It is real.
Here's the biggest rabbit hole you can go down. Alec has multiple videos just about dishwashers.
You can curse me later when you've spent 2 hours learning about Christmas light colours and LEDs.
Just mind that his is a mostly American-centric view. Here in Europe my dishwasher is hooked up to the cold water. Energy usage is negligible.
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Yes, as many others have said, there is an explanation for running the hot water before turning on the dishwasher.
However, your partner is wrong. The purpose of running hot water is to prime the hot water pipes. Once that's done you can go ahead and wash your hands with cold water, because the hot water pipe is already full of hot water.
EDIT: just to elaborate on the above comment:
You can run a mix of hot and cold water all you want, if the hot water is on, it still primes the hot water pipes with hot water; they don’t mix until they join in the faucet itself.
Running the hot water at the faucet will fill the hot water pipe with hot water (hasn’t had time to sit and cool down) so your dishwasher’s initial pre wash cycle has a higher temperature water to begin with as it draws from that same pipe; you’re not starting with slightly cooler water and waiting for the heating element to bring it up to temp (at least not as long, usually dishwasher water is slightly hotter than water heater temp).
Running cold water at the sink does not cool the dishwasher’s intake water down. Cold water isn’t mixed with hot until it’s already in the faucet (after the valves you control at the faucet itself). As long as you run the hot until hot water makes it up to the sink itself, you’re golden no matter what else is going on.
Thanks, everyone else was missing this point and I was about to write up something similar.
You don't see the giant bent calrod in the bottom?
This is primarily a North American concern. A 15amp 120V circuit does not heat water fast enough for the pre-wash cycle to actually have hot water in it. The wash cycle will eventually get hot water but not until at least halfway through, so for half of it you're washing with cold/warm water at best. Depending on what you're washing, that may be okay, but the dishwasher will definitely wash better if it is connected to the hot water supply and the hot water pipe is pre-filled with hot water by running the tap at the sink. European dishwashers are often connected to cold, because they have 220V+ heating elements that can deliver a lot more heat energy and they are designed for this. North American dishwashers are not.
The drain does not matter, you can pour whatever you want down the drain. The concern is on the supply-side only, and only applies if the dishwasher is in fact connected to the hot water line (which it should be, in North American installations, but sometimes it is installed wrong)
you can pour whatever you want down the drain
Oh good to know! I was looking for a convenient way to dispose of all the battery acid from my dead 12V batteries 😅
I do, based on an older vid from the guy CADmonkey referenced. My hot tap water gets to about 120°F.
Doesn't work for me. My dishwasher water line is a separate line. It has it's own valve at the manifold.
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