Can You Beat an Energy Star Dishwasher?
A few months ago, my dishwasher stopped working. I had a lot going on in my life at the time, and since I had never fixed a dishwasher before, I knew it would take me considerable effort to learn how to take it apart and fix it. So I delayed that repair and instead tried life without a dishwasher.
Much to my amazement, I found that I actually like washing my dishes by hand! Back in my college days, I had such a negative experience washing my dishes in the dormitory bathroom sink that I never tried again in a full kitchen. It turns out, the process is very fast and easy in the double kitchen sink I now have, and I feel like I am actually spending less time washing dishes than I did when I used the dishwasher. I eventually repaired my dishwasher, but didn’t go right back to using it.
Intuitively, it feels like hand washing is more eco-friendly than using a dishwasher. Especially when I consider the whole picture, including the environmental cost of manufacturing, shipping, maintaining, running, and eventually disposing of the actual machine, plus other factors like pre-rinsing the dishes before loading them to prevent clogs like the one that inspired this whole inquiry. And while many people seem to agree, there are also numerous claims touting the opposite conclusion. Convictions run high on both sides of this argument, but the science runs low.
I zeroed in on an often-cited claim from the Energy Star web site: washing dishes by hand costs about $1300 more in water and energy vs washing with an Energy Star certified dishwasher over the 12 year expected lifetime of the dishwasher. This claim seemed surprising, specific, and credible given the source. I was curious how they came to that number, and I wanted to learn more. So I contacted EnergyStar to request more information about the scientific studies they conducted or referenced in order to reach that number. They were gracious enough to respond. This is an excerpt from the email they sent me:
“On average [study participants] used 42.3 gallons when hand-washing that test load…. The energy consumed during hand washing is from the water heater.”ENERGY STAR Support
Holy steam, 42.3 gallons is a lot of hot water! The average shower, by comparison, consumes about 17 gallons. This information illuminated a potential source of the confusion. While 42.3 gallons may be the average amount of hot water used to hand wash dishes, I suspected that it was possible to do better. But, is it possible to use less hot water when hand washing dishes than an efficient dishwasher uses? Which methods of hand dishwashing are most efficient? And which methods of hand dishwashing are most wasteful? I headed into my own kitchen to find out.
Note: this is a long article, so if you want to skip the details, feel free jump straight to the findings!
Faucet: My kitchen faucet is equipped with a low flow aerator that has a maximum output of 1.2 GPM (gallons per minute). I also have a spray wand off to the side, which has a maximum output of 0.55 GPM.
Sink: I am using a double sink (a sink split into two halves). Each side has a maximum capacity of 10 gallons.
Dishwasher: The dishwasher used in these tests is a Frigidaire LFBD2409LF0B purchased in approximately 2015, with an EnergyStar certification.
Environment: This is not a controlled lab experiment. I am more interested in real world data from a real kitchen. I have taken careful measurements and notes from my real life, which includes hand-wash-only dishes, double-load-days, and half-load-days.
Funding and Bias: This is a citizen science study, conducted at home, by me, because I was curious. No money was exchanged as a part of this study, and I’m not on anybody’s payroll.
Hand Dishwashing Methods, Compared
Part 1: Water-Wise Hand Dishwashing
Considering all the information I gathered in the parameters about water flow rates, I put forth my best effort to optimize my wash routine. On four separate days, I carefully measured my water use and documented my dishwashing strategy. Even in my worst attempt, I used only 5 gallons of hot water, less than a gallon more than my dishwasher’s Energy Saver cycle uses (not counting the pre-rinse water that I would have had to use in addition to running that cycle). My best attempt used only 2.5 gallons of water per load, nearly twice as efficient as the dishwasher. As long as I was being careful of my water usage, I never came anywhere near the 42.3 gallon average.
Soaking In The Wash Basin
- Water Use: 5 Gallons
- Time Spent: 25 Minutes
- Notes: Since many of these dishes would have needed a pre-soak treatment even if they were being washed in the dishwasher, I would have needed 2-3 gallons of soaking water in addition to whatever the dishwasher uses.
With both sides of my double-sink clean and empty, I plug the drain in one side, add 1-2 TB of detergent, and turn on the hot water. As the hot water runs, I scrub some of my cleaner dirty dishes, the ones that don’t need soaking, and move them to the other side of the sink without rinsing. By the time a couple of inches of water have accumulated in the sink, I’ve typically finished with the original pile of dishes. I turn the water off. I continuously add dirty dishes to the reserved soaking water in the basin. Without running any more water, I use the soapy water in the sink to scrub those dishes, and when each one is scrubbed, I move it over to the other side of the sink. If there are more dishes, I keep repeating this process without using any additional water until all the dishes are scrubbed.
When all that is left is to rinse, I lift each soapy dish and individually, hold it over the basin filled with water, and spray it clean with the wand. That way, all the rinse water is collected in the basin for measurement. Note that use of the spray wand here contributes to efficiency, since it uses much less water than the main faucet, and because the water is more pressurized, it cleans the dishes faster.
If you anticipate generating more dirty dishes later in the day, you can leave the soaking water in the sink and reuse it until it becomes too dirty.
Reduced Soaking Water
- Water Use: < 4 gallons
- Time: 30 minutes
- Notes: I also washed a clay pot that did not fit in the dishwasher (not pictured), and some recyclables and plastic wrappers for ecobricks. That clay pot isn’t dishwasher safe, so I would have needed at least a gallon of additional water to soak and hand wash it separately, over and above whatever the dishwasher used.
I begin with a clean sink, plug the drain on one side, add soap, and begin filling the basin with hot water as I wash dishes. This time I only allowed 2 gallons of wash water to accumulate in the sink instead of 3. I scrubbed all the dishes in this 2 gallons of water. I found it worked just as well as the 3 gallons in Method 1. It took a little more time, due to smaller but more numerous soaking batches.
Fixed Position Wand
After a couple days of careful wash optimization, I contrived a slight modification to my setup. I mounted the spray wand onto the main faucet using two rubber bands. This allowed me to use both my hands to rinse the dishes, without having to hold the wand in one hand. This made it easier to rinse the plates, but harder to rinse the insides of glasses and bottles.
(Reminder: the reason I want to use the wand is to save water, because the flow rate of my wand is much lower than my faucet, while being more pressurized.)
Days With Multiple Loads & Reusable Soaking Water
- Washed: one very-full-dishwasher-sized load and one pretty-full-dishwasher-sized load
- Water Use: 5 gallons for two loads, an average of 2.5 gallons per load!
- Time: ~50 minutes
- Notes: In addition, I cleaned all the day’s recyclables in the same soaking water.
On the days when there are multiple loads of dishes to be washed in the same day, there is an even greater opportunity for water savings when hand washing by reusing the primary soaking water all day.
Part 2: Low Effort Hand Dishwashing Methods
We have seen how water and energy is used in hand dishwashing when a person is actively trying to conserve resources. Obviously, there are myriad ways to waste water while washing dishes, and I can’t test them all. But I did examine four specific short-cuts that I think are pretty common.
Not Fitting The Faucet With Low-Flow Aerators
You’ll recall from the Parameters section that I’m using a low-flow aerator and a super low-flow spray wand. Normal (not low) flow kitchen faucets output about 2.2 GPM. If you have one of these 2.2 GPM faucet aerators and you run hot water for 19.2 minutes, you have used 42.3 gallons of hot water like the participants in the Energy Star study.
If you have a 1.2 GPM aerator like the one I use on my faucet and you run hot water for 35.2 minutes, you have used 42.3 gallons like the participants in the EnergyStar study.
Using the spray wand with 0.55 GPM output, you would have to run hot water for 76.9 minutes to match the 42.3 gallons used by participants in the study.
Using The Main Faucet Instead Of The Spray Wand
In my own tests, regardless of how much water was allowed to accumulate in the wash basin, I used about 2 gallons of rinse water each time with the spray wand.
If I had not used the spray wand and instead used the faucet with 1.2 GPM aerator, I would have increased that rinse water usage to about 4.3 gallons, bringing my total water use to about 7 gallons.
If I had used a faucet with a not-low-flow 2.2 GPM output, I would have used about 8 gallons of rinse water, bringing my total use to about 10 gallons.
These numbers assume that the dishes are pre-soaked, pre-scrubbed, and arranged in a way that facilitates quick rinsing. More time rinsing would increase the number of rinse water, as described above. I suspect I could rinse even faster if I had a dish drying rack. I could place the drying rack in the empty half of the sink, load it with the scrubbed-but-still-soapy dishes, and aim the spray wand at the fully-loaded drying rack to rinse all the dishes at once. Since I don’t have a drying rack, I stack them neatly in the empty half of the sink and lift one at a time for rinsing.
Running Water While Scrubbing
Since it took me about 30 minutes to hand wash an entire load of dishes each time, if I had left the faucet running that whole time I would have used about 36 gallons of water. Without the low-flow aerator, that could be as much as 66 gallons. Wow. I think I see how the Energy Star study came to an average of 42.3 gallons used. This is one method we should all stop using. I cringe to think that I used to pre-rinse my dishes this way before loading the dishwasher, thinking it too wasteful to fill up the sink and soak them. Going forward, I will always use the wash basin method, whether I’m pre-rinsing before running the dishwasher or hand washing the dishes. Not only does filling the wash basin appear to save significant amounts of water, it is much easier and faster to do. Soaking my dishes this way is also responsible for the time savings benefits I noticed when I switched to hand washing. If you don’t have a double-sink, you can buy a wash basin that nests inside your sink and fill that, or you can fill the whole sink and then drain it when you’re ready to rinse.
Filling The Whole Sink
Instead of carefully filling only 2-3 gallons of soaking water in my sink and soaking my dishes in batches, admittedly it is easier to fill the sink most of the way up and soak all the dishes at once. Since the capacity of one side of my sink is ten gallons, the most I would use is 8 gallons. This increases my total use water from 4-5 gallons to about 10 gallons.
Electricity As Water
Even if you live in an area where water is not scarce (as I do), there is an energy cost associated with water use, especially with hot water use. To calculate approximate energy used by an electric water heater similar to my own, I used the data here.
- Approximate Energy Used To Heat 1 Gallon Of Water: 0.195 kWh
My water comes from a well on the property, so I see the energy cost of the well pump and pressure tank included in my electricity bill (we have solar power, but it’s a grid-tied system). Even if you have city water, there are machines involved in pumping, filtering, and pressurizing the water that runs from your faucet. It is very difficult to determine exactly how much electricity is used to pump water, because there are so many unknown variables. I put forth my best effort to come up with an average number that could roughly represent energy used to deliver a gallon of water to a faucet. I used this publication as a guideline to find an approximation of the energy required to pump and pressurize one gallon of water.
- Average Well Depth In My Area: 60′
- Average Pump Height: 10′ higher than the bottom
- Average Pump Efficiency: 60%
- Average Home Water Pressure: 55 psi
- Approximate Energy Required To Pump and Pressurize One Gallon of Cold Water: 0.00066
Combining those numbers, one gallon of hot water carries an energy cost of approximately 0.196 kWh.
Dishwasher Cycle Water Use
|Pots & Pans||9.1||150||1.78|
|Normal Wash + Hi-Temp & Sanitize||8.1||120||1.59|
**Note: The water used by the dishwasher is sourced from the hot water hose. This means that the water going into the dishwasher is already hot, so when we compare gallons of water used by the dishwasher to gallons of water used in the sink, that is a fully equivalent comparison in terms of both water and electricity per gallon. But the dishwasher also uses electricity in order to run, in addition to the energy already used to heat the water. Unfortunately, I have so far been unable to find out how much electricity the dishwasher uses.
If you turn on the faucet full blast and leave it running while you scrub and rinse all your dishes, then you could be using up to 66 gallons of hot water every time you wash your dishes. That’s almost as much as four average showers, and carries an approximate energy burden of 12.9 kwh. If this is sounds familiar, then you have some room for improvement, and you have some options. One way to reduce water and energy use over that particularly inefficient method of hand dishwashing might be to purchase an efficient dishwasher. But that is by no means the only way to wash dishes efficiently. If you learn to wash your dishes carefully by hand, doing all your soaking and scrubbing in a shallow wash basin with the faucet off and then quickly rinsing the soap off of them after they are already clean, you can beat or tie an efficient dishwasher in terms of water and energy use, as I did.
Even if you take a few short cuts and use a little more hot water than the dishwasher uses, there is still a strong argument to be made that washing dishes by hand is more environmentally friendly than owning a dishwasher. Consider the noteworthy environmental impact of mining, manufacturing, transporting, and disposing of all the components in the dishwasher machine. Consider the electricity used to run the dishwasher, over and above the energy needed to produce hot water, and whether you need to run extra hot water to soak or pre-rinse the dishes before loading them into the machine. Consider the ongoing maintenance of the machine. And consider the satisfaction we can gain by relying on our own hands and minds instead of the global industrial system.
Since I already have a dishwasher, I think I’ll keep it for hectic days when I feel compelled to save a little effort, and on those days I’ll pre-soak my dirty dishes in the wash basin instead of rinsing them in running water. But when this dishwasher is done, and it is send off for disposal, I don’t plan to buy a new one. It is no longer a priority for me to own a dishwasher, now that I have learned to wash my dishes quickly and efficiently by hand. If your needs are different from mine and you feel you get great value from your dishwasher, then keep using it in good conscience, because it seems this is a pretty efficient device as far as devices go. Perhaps you are better able to reduce your environmental footprint in another way, maybe by driving less, buying used, hanging your laundry to air-dry, or growing a garden. The world is full of possibilities.