Submitted ⁨⁨15⁩ ⁨hours⁩ ago⁩ by ⁨CombatWombat@feddit.online⁩ to ⁨[deleted]⁩

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?

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dhork@lemmy.world ⁨15⁩ ⁨hours⁩ ago
The Technology Connections guy on YouTube thinks so

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- Rothe@piefed.social ⁨5⁩ ⁨hours⁩ ago
  If you live in the US. Dishwashers works very differently in Europe for example.
  
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  - ValiantDust@feddit.org ⁨4⁩ ⁨hours⁩ ago
    Ah thanks, I was beginning to question everything I thought I knew about how my dishwasher works.
    
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- Gerudo@lemmy.zip ⁨15⁩ ⁨hours⁩ ago
  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.
  
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- someguy3@lemmy.world ⁨14⁩ ⁨hours⁩ ago
  Technically I think he says that IF your dishes don’t already get clean.
  
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  - Aeao@lemmy.world ⁨14⁩ ⁨hours⁩ ago
    Yeah if you aren’t having issues why make the extra step
    
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- lol_idk@piefed.social ⁨8⁩ ⁨hours⁩ ago
  Yes. I’ve watched all of them in their entirety
  
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CubitOom@infosec.pub ⁨8⁩ ⁨hours⁩ ago
The technology connections guy says it helps assuming your dishwasher water connection is at the sink and that the heating element in your washer probably sucks.

Detergent packs are kinda wishy-washy (Dishwashers Explained)

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- lucullus@discuss.tchncs.de ⁨4⁩ ⁨hours⁩ ago
  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.
  
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VibeSurgeon@piefed.social ⁨7⁩ ⁨hours⁩ ago
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

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- bananabread@lemmy.zip ⁨4⁩ ⁨hours⁩ ago
  I was so sure the answer was going to be no. TIL
  
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- khannie@lemmy.world ⁨7⁩ ⁨hours⁩ ago
  
  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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  - VibeSurgeon@piefed.social ⁨6⁩ ⁨hours⁩ ago
    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.
    
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  - echodot@feddit.uk ⁨6⁩ ⁨hours⁩ ago
    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.
    
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BlameThePeacock@lemmy.ca ⁨15⁩ ⁨hours⁩ ago
It is real.

Here’s the biggest rabbit hole you can go down. Alec has multiple videos just about dishwashers.

youtu.be/jHP942Livy0

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- Damage@feddit.it ⁨14⁩ ⁨hours⁩ ago
  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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  - qupada@fedia.io ⁨14⁩ ⁨hours⁩ ago
    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.
    
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- CombatWombat@feddit.online ⁨15⁩ ⁨hours⁩ ago
  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.
  
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lemmyng@piefed.ca ⁨12⁩ ⁨hours⁩ ago
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.

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- 4am@lemmy.zip ⁨10⁩ ⁨hours⁩ ago
  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.
  
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cecilkorik@lemmy.ca ⁨10⁩ ⁨hours⁩ ago
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)

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neatchee@piefed.social ⁨8⁩ ⁨hours⁩ ago
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

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dual_sport_dork@lemmy.world ⁨15⁩ ⁨hours⁩ ago
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.)

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.)

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then_three_more@lemmy.world ⁨10⁩ ⁨hours⁩ ago
Is this an American thing? Dishwashers run off the cold water and heat it up themselves over here.

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- Rivalarrival@lemmy.today ⁨7⁩ ⁨hours⁩ ago
  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.
  
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  - Rothe@piefed.social ⁨5⁩ ⁨hours⁩ ago
    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.
    
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gagootron@feddit.org ⁨7⁩ ⁨hours⁩ ago
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.

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Nomecks@lemmy.ca ⁨12⁩ ⁨hours⁩ ago
The dishwasher has a heating element inside and it’s using maybe 4-5L max for the wash cycle. It heats up pretty fast.

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- Onomatopoeia@lemmy.cafe ⁨6⁩ ⁨minutes⁩ ago
  Not in the US. www.youtube.com/watch?v=_rBO8neWw04
  
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Forester@pawb.social ⁨9⁩ ⁨hours⁩ ago
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.

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HejMedDig@feddit.dk ⁨15⁩ ⁨hours⁩ ago
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

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- crank0271@lemmy.world ⁨14⁩ ⁨hours⁩ ago
  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.
  
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  - Dagnet@lemmy.world ⁨12⁩ ⁨hours⁩ ago
    100% does considering my country doesn’t even have hot water lines
    
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someguy3@lemmy.world ⁨14⁩ ⁨hours⁩ ago
Technology connections 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 stiill 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.

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Brkdncr@lemmy.world ⁨14⁩ ⁨hours⁩ ago
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.

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- NaibofTabr@infosec.pub ⁨14⁩ ⁨hours⁩ ago
  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.
  
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  - Brkdncr@lemmy.world ⁨14⁩ ⁨hours⁩ ago
    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.
    
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- shads@leminal.space ⁨14⁩ ⁨hours⁩ ago
  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…”
  
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  - Brkdncr@lemmy.world ⁨11⁩ ⁨hours⁩ ago
    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.
    
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gaiussabinus@lemmy.world ⁨9⁩ ⁨hours⁩ ago
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.

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- isleepinahammock@lemmy.blahaj.zone ⁨8⁩ ⁨hours⁩ ago
  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.
  
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CompactFlax@discuss.tchncs.de ⁨15⁩ ⁨hours⁩ ago
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.

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- CombatWombat@feddit.online ⁨15⁩ ⁨hours⁩ ago
  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.
  
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  - CompactFlax@discuss.tchncs.de ⁨13⁩ ⁨hours⁩ ago
    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.
    
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  - Beacon@fedia.io ⁨14⁩ ⁨hours⁩ ago
    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
    
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FuglyDuck@lemmy.world ⁨12⁩ ⁨hours⁩ ago
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.

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- Onomatopoeia@lemmy.cafe ⁨6⁩ ⁨minutes⁩ ago
  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.
  
  www.youtube.com/watch?v=_rBO8neWw04
  
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Reyali@lemmy.world ⁨14⁩ ⁨hours⁩ ago
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.

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Kazel@lemmy.dbzer0.com ⁨8⁩ ⁨hours⁩ ago
no!

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viral.vegabond@piefed.social ⁨15⁩ ⁨hours⁩ ago
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.

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- Arcanepotato@crazypeople.online ⁨14⁩ ⁨hours⁩ ago
  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.
  
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dualcoreduron@lemmy.world ⁨15⁩ ⁨hours⁩ ago
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.

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- dualcoreduron@lemmy.world ⁨15⁩ ⁨hours⁩ ago
  And yeah, the hot water cleans better, especially if you have stuck on food.
  
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- dualcoreduron@lemmy.world ⁨15⁩ ⁨hours⁩ ago
  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. youtu.be/jHP942Livy0?is=KOvmqlGaLBekpM6Y
  
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the_q@piefed.social ⁨15⁩ ⁨hours⁩ ago
You guys don’t hand wash?

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