Should you run your sink until the water comes out hot before you start your dishwasher?
Today, I washed my hands at the kitchen sink while making lunch, and was unexpectedly chastised by my partner because she had just started the dishwasher. Apparently, she has recently come across something that has convinced her that running the hot water in your sink means the water that enters your dishwasher will be hotter (checks out), and thus the dishes will be cleaner. I tried searching startpage to see if this is real, but I couldn't make it through even one llm-slop-ticle about it before my eyes rolled back into my head, so here I am asking y'all: chat, is this real? Doesn't my dishwasher have a heating element? Is there any meaningful difference between heating the water with a hot water heater vs a dishwasher, other than I can't use my sink while the dishwasher is filling and I have to pour a bunch of cool water down the drain?
131 replies
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.
Growing up we had to run the shower until it was hot before we could wash the dishwasher.
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.
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.
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?
https://us.mieleusa.com/MieleMedia/docs/operatinginstructions/Old-Archive/Residential/Dishwashers/English_manuals/Installation_Instructions/Full_Size_install.pdf
"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.
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.
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)
I run the dishwasher every night, even if there's just a few dirty dishes, so I'm pretty hard on my dishwasher. I use the heck out of it.
It's caused lots of wailing and gnashing of teeth in my family but I can't stand unloading a dishwasher packed to the gills with a week's worth of clean dishes. Just get it done as part of a daily routine.
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.
Yup, and that's why some dishwashers include PreWash text somewhere on the side of the door. Sometimes it's even on that little flap where you put the pod
So do dishwashers in North America they are just less powerful because of the 120 volt.
Crazy. Mine only takes in cold water. Never even knew ones that take in hot water existed.
You'll be surprised to hear that U.S washing machines have the same setup, and this is why they talk about "wash cold" or "wash hot" instead of having specific temperatures on their washing programs like 30 C, 40 C, 60 C etc.
How do you do a 90°C wash? Surely the tap water doesn’t get that hot.
The washing machine heats the water, many go up to 95°C
I wouldn't know unfortunately, I'm in Europe.
As a European that carefully checks the temperature levels indicated on the clothing before washing, I feel like I did it wrong - or at least overly complicated - my whole life now 😅
It's because the US electrical system sucks and they refused to upgrade it, although reasonably speaking it would be kind of impossible at this point. In order to be able to actually run a heating element you would have to have a special circuit fitted with a decent voltage.
it's pretty trivial to combine two hots to get back up to 240. It's common for industrial and some consumer appliances
Also why US homes tend to have the immersion heater setup for hot water with a big tank that gets heated over time, compared to the common euro system of on-demand instantaneous hot water.
I gotta love how the US is really advanced for the most part but then occasionally you come across one area in which it operates like 1980s Estonia.
The water heaters are usually gas here though, so electric system doesn't really matter. Tankless heaters have become a lot more common over past decade or two, both gas and electric. For electric ones you just use a 240V circuit. Most electric appliances that need a lot of power run on 240V here, 30A and even 50A or 60A circuits are common and provide enough power for household needs.
The newest construction near me puts tankless in townhomes and full-size in single-family homes. (as long as gas is available)
They're super efficient when you don't use tons of hot water because your waste on tank heaters is heat loss through the pipes and heater itself.
Ah that makes sense. Cheers.
I was so sure the answer was going to be no. TIL
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)
Provided your dishwasher is even connected to the warm water line. Typical dishwashers with internal heaters are not. A family member of mine has the dishwasher connected to the warm water line to save on electricity for heating the water (has solarthermal elements on the roof for heating water). Though that can alao mean, that on hot days the warm water line gets too hot for most plastics (like 70°C). A bit inconvenient.
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.
I noticed an improvement preheating the water. It's also probably more energy efficient than letting the dishwasher do it, if it can at all.
They both have electric heating elements so identical efficiency. The advantage is that priming hot water means it’s hotter for longer and reaches a higher peak temperature in the dishwasher, which means more effective cleaning.
Not every home heats their water with electric resistance heating. My previous place used natural gas for hot water, and my current home has a heat pump water heater, which has an effective efficiency much greater than a normal electric water heater.
The heating element in the dishwasher at best maintains the water at a warm temperature. It will not instantly heat the water up for the very short first cycle of prewashing, just like if you suddenly put cold water into a water heater it wouldn't be suddenly hot. It takes a lot of energy/time to warm water up.
My statement is taken directly from TCs video where he graphed the temps for primed vs unprimed washing. Priming the water leads to hotter (higher peak) and more area under the curve. Not priming leads to lower peak temps, but it’s certainly warmer than at best warm. The element will heat your water up even hotter than it comes out of the primed line, assuming you primed it.
When I open my dishwasher it is absolutely steaming and the dishes are too hot to handle. This temperature is above the setting on the hot water heater, ergo this extra heat can only have come from the heating element. It provides significant extra heat.
You are correct that it will take significantly longer than the prewash cycle’s duration and is not something to be relied on if you want optimal washing.
If you live in the US. Dishwashers works very differently in Europe for example.
Indeed. Both apartments I’ve lived in (in Europe) had the dishwasher hooked up to the cold water feed, so preheating the water would absolutely do nothing at all.
Ah thanks, I was beginning to question everything I thought I knew about how my dishwasher works.
Reliably having 3 phase 230 V (thus 400 V delta between two phases) makes a big difference from single phase 120 V. Usually rated at 16 A too, available from each phase pair.
Almost 10 kW available at the peak (although almost nothing made for regular homes use it that much, aside from electric cars).
https://everycalculators.com/kilowatt-calculator-3-phase.html
As compared to a US outlet typically limited to 20 A at 120 V in one phase, giving you 2,4 kW (a quarter) or 15 A at 1,8 kW.
Technically I think he says that IF your dishes don't already get clean.
Yeah if you aren’t having issues why make the extra step
Yes. I’ve watched all of them in their entirety
You don't see the giant bent calrod in the bottom?
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.
It is real.
Here's the biggest rabbit hole you can go down. Alec has multiple videos just about dishwashers.
https://youtu.be/jHP942Livy0
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.
European dishwashers seem to be designed vastly differently to American ones.
Water efficiency goals specifically; I've seen consumption of 7 US gallons (26.5 litres) per cycle called "eco" on American dishwashers, where mine (Miele) claims 12 litres on the heaviest cycle.
The manual for mine calls out connecting to hot water as a way to increase efficiency if you have hot water with a >1 COP, mentioning solar or heat pump cylinders.
A professional I asked noted though that for protein-heavy residues (like egg), hot water could bake it on before the dishwasher starts cleaning it.
And a little detergent in the pre-wash helps a lot with that. (My machine, a Bosch, does not have a pre-wash compartment so I just spill a little when I fill it.)
Alec recommends powder detergent, and simply pouring some outside the compartment if there's not a dedicated one for pre-wash
thank you. I'm supremely annoyed that I'm reduced to posting to fedi to find good sources for a basic adulting question, but I'm equally grateful when someone comes through for me.
Always try to be one of today's lucky 10,000: https://xkcd.com/1053/
If you read the dishwasher manual you’d find it in there.
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)
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.
It's just to get the hot water flowing in the hot water line. So your dishwasher doesn't get as much cold water as it would other wise.
The manifold they're referencing is probably closer to the water heater than the sink. More specifically, it's probably in their basement or garage. It's unlikely that running hot water from anywhere will clear those lines.
@[email protected], if it begins to bother you too much, do what we did at my friend's house and turn off the dishwasher supply valve and install a splitter at the sink's hot water supply valve. I'm obviously making numerous assumptions on how close your dishwasher is to the sink and how accessible everything is.
Yes. Foolishly most of the less expensive dishwashers don't heat the water themselves, and the first cycle is more effective if it doesn't have a period of using cool water from the pipes until the hot water arrives.
I was skeptical at first too but it truly works.
But it may be worth clarifying to your partner that once the water is coming out of the tap hot, the water in the hot pipes is already hot, so turning the tap to cool at that point no longer negatively impacts the dishwasher.
The important part is getting the cool water in the hot water pipes that has been sitting there flushed out before starting the dishwasher. If that's already achieved, then what you do with the tap doesn't matter anymore
Why did your wife chastise you over having cleaner dishes?
Is this an American thing? Dishwashers run off the cold water and heat it up themselves over here.
Plumbing code in the UK (and parts of Europe?) allowed/allows hot water tanks to be open to the atmosphere, to prevent boiler explosions. The specific tanks in question are filled via float valve, much like a toilet tank. Being potentially exposed to airborne bacteria, fungi, and other biological material, water out of these tanks is not considered potable. If you have one of these atmospheric pressure heaters, you shouldn't consume the water, or clean cookware, dishes, and utensils with it. Because they might be installed in buildings with atmospheric pressure hot water, dishwashers in areas with atmospheric pressure hot water tanks are designed to be connected to the potable, cold water supply, rather than a potentially contaminated hot water supply.
US does not allow atmospheric pressure hot water tanks. US tanks are under positive pressure, using T&P valves to protect against excess pressure and boiler explosion. The water in US hot water tanks is considered potable. Dishwashers in the US do have heating elements, but they are designed to be connected to a hot water supply.
This is also why UK taps typically have two spouts. The cold water side is pressurized; the hot water can be gravity fed. This causes two problems: 1. If there is any restriction in the output, cold water can backfeed the hot supply and overfill the hot water tank. 2. non-potable hot water can contaminate the cold water in a mixing valve, rendering the cold water non-potable as well.
Sounds like a legacy thing. The vast majority of houses now have combi boilers so no hot water tank. Hot water is on demand. Which would also be why separate taps have pretty much disappeared from UK homes since at least the 2010s.
Though I do think it's very likely that a big chunk of it is as the other commenter said, an electricity thing.
With the price of gas what it is over here at the moment I'm rather glad my dishwasher is electrically heating as I can run it even on a dull day and my pannels will provide a good chunk of the power.
Exactly. UK and European legacy standards required cold water dishwashers; US legacy standards called for hot water dishwashers. Once that expectation took hold, it's somewhat difficult to alter it. Builders install plumbing for their respective systems; consumers buy appliances to match their plumbing. It's a vicious circle with little compelling reason to break it. Neither is objectively better; neither is objectively worse.
The overwhelming majority of households had gas-fired water heaters, because for decades, it was significantly cheaper than electric, and those gas-fired systems remain in place in a majority of homes. In that sense, it's an electric thing.
In the sense that US circuits simply can't handle the current requirements of a permanently installed heating appliance, that is a complete myth. Trust me, we know how to
wasteuse electricity.It has nothing to do with that. It is about the electrical system in the US not being able to supply water heaters in dishwashers and washing machines. Also the system you are describing is certainly a UK-centric one.
That is a myth arising from US typical residential circuit standard being 20A @ 120V, or 2400W.
Major appliances are not limited to this typical standard. US/Canada have code for and commonly install dedicated 30A@120V, (commonly used for large through-window air conditioners) as well as 240V circuits rated from 20A to 80A. The North American electrical system typically provides 200A @ 240V to the residence. That's sufficient for heating hot tubs and in-ground pools.
No, the decision to use hot water instead of cold water arises primarily from plumbing factors, not electrical.
It's because I have never seen a dishwasher in the US designed for a high current circuit.
The standard is a single dedicated 15amp circuit for the dishwasher, because the standard dishwasher is designed to use the house hot water, so doesn't need a larger circuit for a water heat cycle at the start.
Since US homes have a built-in, stable hot water supply, why would you build further pre-heat into a dishwasher?
It has fuck all to do with the water supply,
Right. But, if they did make a 5000W dishwasher, it would not be difficult to power it in the US. Even though typical NEMA 5-15 and 5-20 outlets can only handle 1800/2400W, US electric code provides for 50A@120V, 20A@240V, and much, much larger circuits for ranges, water heaters, hot tubs, pools, arc welders, air compressors, etc. There is no electrical limitation preventing adoption of cold-water dishwashers.
I feel like this is only a concern if you keep having poorly washed dishes. And if that’s the case, I would opt for a new dishwasher.
Yes. For a typical American dishwasher installation, anyway, where the dishwasher is connected to the hot water line which is in turn connected to your storage tank water heater.
First, your water heater is already full of hot water that you've already paid the energy cost to heat up. It's therefore nonsensical to deliberately pump cold water from the line into your dishwasher only for the dishwasher to have to heat it up (using energy/money) and then have your water heater also heat up the displaced water inside it that was just pumped out.
On dumb dishwashers that don't do anything to sense the internal water temperature, this will also moderately improve your wash performance. (GE calls this feature "Automatic HotStart," for instance. Other brands call it something different. These machines will pause and run their little internal water heater coil at full blast until their current charge of water is at a temperature their programming considers acceptable to start the cycle. There is no performance detriment in this case, but it will cost you time and more energy/money.)
Modern dishwashers use a surprisingly small amount of water per cycle. Usually somewhere around 3.5 gallons for the entire thing from start to finish. This is contrary to what your parents think, who will insist to you they can totally hand wash an entire sink of dishes with "less water" than that wasteful dishwasher, which they absolutely cannot. Your dishwasher is not consuming water the entire time it is running. It will fill and recirculate that fill's worth of water inside itself, usually going through 3 or 4 phases of filling and draining throughout the cycle to arrive that that final water usage figure of around three and a half gallons. Therefore it does not readily have access to hot water unless you've primed it by running your sink, as what used to be hot water in your pipes rapidly cools off when said water is not flowing. Your dishwasher probably will not draw in enough water in one fill cycle to purge all of the standing cold water that's in the pipe unless the distance from your water heater to the dishwasher is unrealistically short.
(The latter actually is the case for the dishwasher at my office, which is fed by an undersink "low boy" water heater that's directly next to it and only separated from the dishwasher by a grand total of about 18 inches of pipe.)
The hot water will be missing from the tank and has to be replaced with cold water that needs to be heated up again. So shouldn't the amount of water that needs to be heated be the same in the end?
More than that, you will be pumping more water to flush the cold water from the line, which is more energy. You will use more water overall because that cold water will all be going down the drain. You will then have to heat up enough water to match the cold water you flushed from the line plus the water used to wash your dishes to reheat your water tank. If, from an energy/cost perspective, that is less than what it would cost for the likely less efficient water heater in your dishwasher to heat the water, then you have saved some money. If it isn't, and your dishes are already coming out clean, then you are neither getting a better nor more efficient cleaning job done.
Maybe take a look under your sink and check if the dishwasher is connected to the cold or warm water line. It only matters if it is connected to the warm line.
Depends on how the dishwasher is connected, but I would assume it's connected to the cold water. At least that's the common way in Scandinavia
That's a good point. I think in the US it's connected to the hot water line, so the answer to this probably differs by region.
100% does considering my country doesn't even have hot water lines
Yes, hot water cleans better, and results in dryer dishes due to condensation drying.
The heating element in a dishwasher is weak. It can’t heat water up that well since it’s limited to 120v and probably not even 20A. The first rinse cycle will effectively be cold water.
Your tank water heater is 240v and has a dedicated circuit, probably 30A. It can heat a lot of water, fast.
If you’re concerned about wasting water you can get a small tank or tankless hot water heater under the sink. Your water will then be hot nearly always.
Some wash cycles will both purge more water and heat it up longer to compensate.
The water heater tank is also insulated better than your dishwasher because it doesn't have a big door on it. Even if the heating elements were the same, the water heater would be more efficient at heating water and keeping it hot due to less energy loss.
They are both 100% efficient, although 240v has less loss over the same amount of length.
Insulation doesn’t matter too much if you’re just dumping the water down the drain.
But you’re right a dishwasher doesn’t have nearly as much insulating properties. The heat element in one is basically there to counter act the heat loss.
Different country and all, but both are 240v in my neck of the woods, and since I live on tank water with mains water supply as a back up. Coupled with what I believe may be the most circuitous route from hot water cylinder to kitchen tap on earth (3 meters point to point yet seeming out to the local post office and back based on how long it takes to get hot water out of the tap) we use the Dishwasher to heat our water.
Which is all a very verbose way of saying "It depends on your circumstance..."
US doesn't get 240v at most outlets unfortunately. My hot water to the kitchen is 50-60 ft as it goes up to the 2nd floor attic, across maybe 45 ft, then back down.
Takes a couple of litres of water before we get hot water. I have filled the kettle twice before the water was too hot to hold my hand under before. That's roughly 3.5 litres of water just to get to the hot stuff. Luckily boiling water was a key consideration in our voltage level (actually that's something I made up on the spot 😜) but more power equals good so... Its weird that this is a field that the US apparently just decided to let a large portion of the world be more "powerful" almost expect that if there were parts of the world settling on 240v the US would arbitarily decide they needed 500v.
Are you going to pay to change the entire electrical grid, rewire every house, replace every appliance, etc.
It would be an unimaginably massive undertaking for very little gain.
The US electrical system was well-established when Europe had to rebuild post-WWII.
I always thought the decision was made a lot earlier than that. Wasn't it largely due to Westinghouse that America settled on 60hz 110v? Where AEG pushed 50hz 220v in Europe? That was late 1800s early 1900s from memory. World war 2 may have resulted in some rebuilding but they rebuilt along lines that were already established, the bump up to 230-240v with time and gained efficiencies is mirrored in the US with the move towards 120v at least that's what I recall, but I must admit that outside of some Technology Connections videos I haven't delved too deeply in recent years (and yes I know Alec would say the US technically already sends 240v but that's not what your general appliances are rated to).
The US uses many smaller circuits. I have two appliance circuits, a lighting circuit, a dedicated refrigerator circuit, and a 240V range circuit. Five separate electrical circuits, just for my kitchen.
Rebuilding after WWII, the UK standard was to run a single ring circuit for each floor of the home. They ran as few household circuits as possible, because they needed the copper.
If you look at the amperage/wattage ratings of UK circuits, they are considerably higher than other 220v/240v countries, because their circuits are intended to be shared among many more devices.
You know how they warn you not to plug in too many devices into a single circuit? The UK electrical system took the exact opposite approach, because they needed to. This is why they have a fancy plug that nobody else in the world uses: it is an essential safety component that serves the same purpose that the household circuit breaker performs for the rest of the world.
Technology Connections (youtube channel) says yes run until it's hot IF you have trouble with dirty dishes, iirc. I think the bigger thing is to clean your debris trap. Also you should be fine washing your hands. The dishwasher will still pull as much hot water as it needs, they are typically only hooked up to hot water so it's not like you having the tap on mixes it up or anything.
You want to make sure the water in the line is hot by running the sin to flush the old settled hot water that has cooled to house temp in the pipe. , once the cold water in the line has been run and replaced by fresh hot water the dishwasher can take hot water and not have to heat it from cold to lukewarm.
The dishwasher has a heating element inside and it's using maybe 4-5L max for the wash cycle. It heats up pretty fast.
Not in the US. https://www.youtube.com/watch?v=_rBO8neWw04
Too much link, not enough answer
I’m not sure why you’re being chastised for using water while the dishwasher is filling. That is a non sequitur. But for most people, the answer is probably yes, it moderately improves performance.
I'm just telling you how I discovered his piece of information. It was a very normal household interaction but with a dash of source amnesia.
edit: I misunderstood how you meant non sequitur. I turned the water cooler to wash my hands because I have soft hands and cannot tolerate the water at full heat.
I had a suspicion. Water coming out of pipes is just kinda black magic for many people (not to be negative, irs just not worth learning about). Because the cold and hot water don’t combine until inside the tap, it doesn’t matter for the dishwasher. But pulling hot water out of the tap gets hot water to wherever the dishwasher ties in - in most kitchens, but not always in fancy ones.
That won't make a difference. You need to pull the hot water up before you start the dishwasher, but after that you can run the sink with pure cold water and it won't change the dishwasher temp at all. The dishwasher is connect to the hot water pipe directly
So everyone else is talking about how yes, it is generally better (at least in the US). But what I think is missing is that once the hot water is there, there’s no reason to not use cooler water at the sink. The dishwasher isn’t pulling its water from the sink, but if the hot water makes it to the sink then it’ll make it to the dishwasher more effectively.
For my specific setup, the hot water from the sink is hot immediately if I've already been running the dishwasher. So, just by that, I'd assume that clearing out all of the cooler temperature water by pre-running the sink could provide some benefit. As to whether it makes a substantial difference or not, I don't know. I'd say it's certainly possible though.
This is the correct answer. Turning on the hot water before the dish washer starts clears out the not-too-hot water that was in the line. They don't use that much water so it apparently makes a difference.
ETA: but washing your hands (with hot water I presume?) won't impact the machine.
The dishwasher has a booster that brings to steaming- much hotter than your full-home water heater should be set to.
I wouldn’t worry about it. The difference in efficiency is negligible.
Not in the US.
US dishwashers run on a 15 Amp circuit so don't have a preheat for the first wash. The heater is too slow.
https://www.youtube.com/watch?v=_rBO8neWw04
How does that change anything in any meaningful way?
The difference between the hot tap and the cold tap is peanuts compared to the difference of hot tap to dishwasher’s hot.
It’s not even all that more efficient- unless you ignore the water heater’s energy use. There is, though some reason to hook up to the cold side any ways- water heaters can get nasty and the water in them is soaking in that nastiness.
no!
No, buy a better dish washer. Mine heats the water after fill and before washing starts. The only reason to do this is if gas heat was cheaper than electric and the money saved is less than the hassle and the waste in doing it.
Let's say you have a kitchen faucet with a high flow rate of 2 gallons per minute. And let's imagine you need to run the sink for a long time, say a full minute. So perhaps you lose 2 gallons of cold water to flush the lines. (Assuming you don't do anything with that water, which you can certainly choose to do so.) Some searching suggests the average cost of water in the US is $5-8 per 1000 gallons. Let's make it a round $10 per 1000 gallons, or a penny per gallon.
So, even with generous assumptions, it costs you 2 cents in wasted cold water as you flush the lines every time you run the dishwasher. If you run the dishwasher every single day, that comes to $3.65 in wasted cold water. If the fancier dishwasher with the better heating element costs only a hundred dollars extra, it will still take 27 years for the extra cost to be paid back via saved water.
In practice, these numbers were chosen to be generous, and the payback period is likely over a century. Your dishwasher will not last 27 years, let alone a hundred. Plus the time value of money. In short, the fancier heating element will never come close to paying for itself. You're paying for a convenience, not saving money.
If you're trying to be savvy about saving water, use the un-hotted hot water supply line water to fill a pitcher. In case the water is too hot, let it cool. Use it to water your plants, fill your pets' water bowl or dispenser, run it through a passive filler jug if you have concerns about water from your water heater, or add a little detergent while it's still warm and go scrub your bathroom floors. Go, do it now, TheFartographer. You've been meaning to do it for days. Get off the Internet and go scrub your filthy bathroom floors right now. Why am I this way?
That's the dumbest thing I ever heard.
It's an old thing that isn't necessarily needed anymore. Technology Connections has a video about it.
You guys don't hand wash?
It's my understanding that dishwashers generally do not have a heating element, so the hot water is coming directly from your water heater. I believe you should run the sink water till it gets hot before starting the dishwasher, and not run cold water until the dishwasher stops filling. They generally share the same line. If the dishwasher had a dedicated water line I imagine it wouldn't make a difference, but most inexpensive dishwasher models and homes share with the sink.
Hot and cold do not use the same line. Dishwashers tap off the hot water pipes to your sink. They also commonly have heating elements. Even my $150 landlord special Midea has one. Running cold water in the sink after it starts has no effect. There’s no cold water connection to the dishwasher.
Yeah, I was wrong about the heating element, but I would still run the water hot. Check out the video I posted
Yeah, I’m echoing my knowledge from that video as well.
And yeah, the hot water cleans better, especially if you have stuck on food.
Ok edit: your dishwasher DOES have a heating element, but it's not enough on its own, so the logic still applies. If you want the full deep dive check this out, I love this guy's videos. https://youtu.be/jHP942Livy0?is=KOvmqlGaLBekpM6Y