It’s counter-intuitive. New dishwashers tend to run a lot longer than older machines, yet the new ones are advertised as using less electricity and less water. “Normal” cycles stretch to two hours and beyond, vs. around one hour for older machines.
These longer run times, judging by messages on Internet dishwasher and appliance sites, have caused people to wonder if something is wrong with their new machines. And, if they are running properly, how could newer technology be so much slower?
I became curious about dishwasher run times after we bought a new one (along with a fridge) to replace a 12-year-old unit that had become distractingly loud.
I checked the Energy Star website for an explanation about the long run times.
The U.S.-based Energy Star program issued new standards that came into effect on Jan. 20, 2012, requiring dishwashers to use less water and energy. Specifically, to receive Energy Star designation (something manufacturers aspire to because it can help boost sales) machines on a normal cycle must use no more than 4.25 gallons (about 16 litres) of water per cycle, and no more than 295 kWh of electricity in a year, assuming a machine runs roughly four times a week. Water entering the dishwasher is expected to be hot enough, and doesn't need to be heated by the machine.
Manufacturers had several years to redesign their machines. There was a dishwasher summit in October 2010 to hash out the particulars.
The objective was to have dishwashers clean just as well despite using less water and electricity. Manufacturers accomplished this, in part, by having their machines run longer. With less water to spray, the machines spray longer, using higher-efficiency motors and pumps.
How this works specifically I am not sure. The fine details appear to be trade secrets. In addition to the longer run times, the better energy efficiency seems to involve refinements to how spray arms work, the design of dish racks, and motors that despite running two and three times as long in a cycle, use less electricity than older motors.
Manufacturers have recognized that selling the concept of more is less can be difficult.
Bosch, a maker of higher-end dishwashers, made this observation in a submission to Energy Star:
“Cleaning performance can be increased and energy usage can be reduced, with longer run times. But consumers relate run time to energy usage, and will often choose to hand wash smaller loads when confronted with long run times.”
I also have trouble getting my mind around this. The dishwasher runs twice as long, but uses less water and power. Seems like magic.
But it’s still possible to return to the good old days with a new machine. The Energy Star standards are based on the “normal” cycle. Nothing stops a manufacturer from including a cycle that is shorter, that sucks up a greater quantity of water and power to produce a more aggressive spray.
On our machine, for example, there’s an express cycle that does the dishes in just under an hour. I can hear the difference. The machine is a little louder, and it sounds like more water is spraying with greater force.
The manual confirms that the express cycle requires more power (without being specific), and more water — 23.5 litres vs. 10.5 to 15 litres on the normal cycle.
- - -
Update, Sept. 17, 2019: A New York Times story about efforts to roll back energy conservation for dishwashers: Inside Conservative Groups' Efforts to 'Make Dishwashers Great Again'. As the article points out, you can easily override the default energy-saving settings if you pick a cycle that washes faster by using more water and electricity.
- - -
This is wisdom repeated on energy conservation websites: Handwashing of dishes uses more water and energy (for heating the water) than a modern-day dishwasher.
There’s a study about this, published in 2004 in Home Energy magazine.
“ . . . we persuaded 113 people from seven countries in Europe to participate in the dishwashing experiment. We compared their use of water and energy and the cleanliness they achieved to the consumption generated by two energy efficient dishwashers. To reduce variability in test conditions, we had most of the test subjects wash dishes in one laboratory at the University of Bonn. For test subjects,we chose visitors who had not lived for too long in Bonn or Germany to ensure that they had not adopted German behavior.To make sure that we were getting a correct picture of the consumer behavior for a specific country, the tests were redone using the same equipment in laboratories in France, Italy, Spain, and the United Kingdom.”
The study confirmed that, when compared with humans, recent-era dishwashers generally do a better washing job while using less water and energy.
- - -
The energy conservation people are anti-rinsing. Don’t waste all that water rinsing your dishes before putting them in the dishwasher. Just scrape. And if you can’t help yourself, at least rinse with cold water instead of warm or hot.
Energy Star even has a Scrape Don’t Rinse logo.
But many dishwasher repair people say rinsing can help prevent a machine from breaking down. They say they rinse before loading their own machines. All that gunk can clog things up. There’s a discussion about this at angieslist.com.
The manual for our dishwasher sets out a schedule for cleaning the filters so that clogging doesn't happen.
It also says that we should run the hot water at a faucet near the dishwasher for a little while before starting the machine. That way, hot water enters the machine immediately.
- - -
A PDF of a presentation from the Oct. 26, 2010 dishwasher summit.
- - -