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?
Counter-question: Why do you ask this online rather than just testing and seeing if it makes a difference?
Also, does it even give bad results anyways? Because i have never once in my life encountered a dishwasher that didn’t get things squeaky clean almost without even needing detergent. I suspect many people worry about the cleanliness of their dishes for absolutely no reason.
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=jHP942Livy0came 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.
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.
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 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.
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.
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).
Growing up we had to run the shower until it was hot before we could wash the dishwasher.
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.
The Technology Connections guy on YouTube thinks so
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.
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
He also said that with modern detergents, you should do colder washes anyway, as the hot water has little benefit.
Yes. I’ve watched all of them in their entirety
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.)
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.
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.
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.
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
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.
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
Ah that makes sense. Cheers.
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
I was so sure the answer was going to be no. TIL
So do dishwashers in North America they are just less powerful because of the 120 volt.
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 😅
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
