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?
Why did your wife chastise you over having cleaner dishes?
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 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.
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.
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
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.
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.
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.
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
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.
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.
I wouldn’t know unfortunately, I’m in Europe.
The washing machine heats the water, many go up to 95°C
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.
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.
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.
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.
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.
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)
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.
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.
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.
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
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.
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
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.
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.
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.)
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.
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.
Sounds like a legacy thing.
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.
Though I do think it’s very likely that a big chunk of it is as the other commenter said, an electricity thing.
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.
It is about the electrical system in the US not being able to supply water heaters in dishwashers and washing machines.
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,
It’s because I have never seen a dishwasher in the US designed for a high current circuit.
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.
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.
