How do modern dishwashers take way longer to run and clean better yet use less energy and water?
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As others said: they trade time for water. I would not say that modern dishwashers get dishes “cleaner” than old ones: they expect you to put them in fairly clean to start with.
My parent’s KitchenAid was made by Hobart, who makes commercial dishwashers too. Other than one burned out (and replaced) motor, it lasted for more than 30 years. It had a beast of a motor, lots of spray jets, a huge and largely self-cleaning filter, filled up its tub before starting, had a Sani Cycle, two soap dispensers (both automatically opening) and a food disposer.
But the big expense was hot water. The cycle plan was like:
Drain (get rid of spilled liquids in the tub)
Pre-rinse 1
Pre-rinse 2
Pre-wash (5 min) -first soap compartment
Main wash (15 min) – main soap compartment
Rinse 1 (5 min)
Rinse 2 (5min)
(Heat water for Sani if selected)
Final Rinse (rinse aid dispense) (8 min)
Hot Air Dry
The whole thing took about an hour. Each wash and rinse cycle put several inches of water in the bottom of the tub.
Today a dishwasher fills with just barely enough water to be able to pump. The “pipes” have a narrower diameter (saves water) and they use a much smaller pump (saves power). As a result there are only a relatively few spray jets, and no water pressure available to spray-clean the filter do you have to remove it and clean it yourself. And the cycle plan is like this:
Prewash (cold water) – 8 min
Main wash (warmer water) – 60 min
Rinse 1 – 20 min
Rinse 2 (hot water, Sani, rinse aid) – 20 min
Dry (passive by default) – 0-30 minutes. (Some machines use condensation drying after the cycle is over).
The efficiency is gained by heating the water less, using much less water, and using smaller pump motors.
A completely different way to look at it: for maximum efficiency, we want the water going down the drain to be as dirty and as cold as we can possibly make it- except for that final rinse, which for safety’s sake should be hot and crystal-clean. So we do as much of the wash with dirty water as we can, and run the wash for a very long time to dissolve as much dirt (grease) as we can-fully saturating the wash water with “dirt” before dumping that water and replacing it.
If you’ve seen a commercial kitchen, they do this. They recycle dirty wash water with a pump and use that to flush big food particles. A spray rinse (a small bit of warm clean water) rinses that dirty water off (which then gets recycled). Only then do dishes go into a commercial dishwasher- which, mostly, makes sure the dishes have been duly cleaned and sanitized at the cost of only about 1 gallon per load.
Hobart now only makes commercial gear. The KitchenAid brand is owned by Whirlpool.
There is some subterfuge in the Energy Star ratings, by the way. If you have to pre-rinse dishes in the sink, it doesn’t count against the dishwasher’s EmergyGuide. Worse yet: if the machine itself last s 8 years instead of 30- there’s a huge hidden cost and environmental impact.
How come nobody is mentioning better detergents? Today’s detergents contain enzymes which break down the grease into smaller soluble parts. So the water temp does not need to go up as high, which improves energy efficiency.
Technology connections has a good video on YouTube that shows the inside working.
Basically they reuse a lot of the water. First it pumps a little water and uses sprayers to get most of the food particles off. They have their own filter and can reuse most of the water. It also does the top and bottom separately so it needs less water total. The machine is also insulated to keep the water hot once it’s heated up. It only replaces the water for the final rinse and steam disinfection cycle. Honestly the heated dry part uses more energy than needed but still less than a water heater.
Compared to a sink which probably takes at least a dozen gallons of hot water to fill up. It takes a lot of energy to heat up that much water. Plus you have to use even more for rinsing. I think the average new dishwasher only uses like 4 gallons for a whole load. So that’s a lot less energy in heating and a lot less water.
The dishwasher uses the water, heats it up and it uses it to wash the dishes. It’s like when you fill the sink up with water. You don’t empty it it until you’re done washing. The dishwasher will use the same water and then drain it and use new water to rinse the dishes and drain again.
Here is the video showing what is actually happening inside the dishwasher.
Then when it is done, it uses heat to dry the dishes like a dryer.
A dishwasher works the same way a washing machine works but it has a built in dryer too. That is why it uses less water than it does when you do it by hand.
This may get buried but I had a professor who focused on sustainability and did a study on this exact topic. She found the major reason was that when people did dishes they let the water run the whole time.
When they had people turn the sink off, soap everything up, then turn it back on to rinse off the soap. Or turn it off and on between each use, the sink was either the same or a little more efficient than the dishwasher.
Heating the water takes much more energy than the spray pumps do.
Turns out if you start with less water, then heat that smaller amount to a lower temperature, but then spray it around for way longer, you get at least as good a cleaning for less energy.
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It’s all to do with efficiency, newer models are more efficient but run slower, heat less water at lower temps (sometimes)
Think of a car doing 100mph, it would take 1 hour to go 100miles and say it burns 5 gallons of fuel (20 mpg)
If the car ran at 50mph it would take 2 hours but might get 40mpg so would only use 2.5 gallons.
Same job done, it took longer but was cheaper.
Also a huge improvement in modern dishwashers is the design. Most of the old crap is either plastic or metal with nearly zero insulation. Modern dishwashers are typically steel tube with a rubber tar like layer melted onto it, and then also come with actual insulation on the outside to aid in heat loss reduction. Also keeps the noise down better.
Next is by design it uses less water, which is good. However the old gel dishwasher detergent is extremely bad, as water saving units do not drain enough water to get that gel crap out of your drain lines, which in term causes pump failure. Only use pods or powder.
Edit, I mean pods which have a small amount of gel, and the rest are powder. Thought I should clarify.
Fun fact, dishwashers use about the same amount of water in 2-3 minutes of washing by hand.
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