How We Test Dishwashers

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The humble dishwasher may be one of the most revolutionary, time-saving inventions of all time. That’s why it’s especially disappointing when you drop hundreds of dollars on a new dishwasher, but your dishes come out dirty.

Here at Reviewed.com, we’re confident that we only recommend the best dishwashers. That’s because our tests are both scientifically rigorous and representative of how the average person does dishes. Want to learn more? Read on.

Installation/Hookup

A lot of dishwashers fail because of improper installation. That’s why we do it ourselves.

We install the dishwashers ourselves.
Credit: Reviewed.com / Julia MacDougall
It can be a messy job, but our reviewers install the dishwashers themselves.

After a dishwasher is unboxed, we connect it up to power and the water input and output hoses. We install inline water and electric meters that allow us to measure the water and electricity usage for each cycle. These measurements make it possible for us to draw conclusions about the product’s efficiency.

Two dishwasher testing stations.
Credit: Reviewed.com / Kyle Looney
Each dishwasher testing station is surrounded by wooden panels and a countertop to simulate real kitchen installation.

Once the dishwasher is safely and correctly connected to water and power, we place it at a testing station that is surrounded by wooden cabinet panels and covered by a countertop—just like it would be in your kitchen.

An Intellifaucet with a temperature near 120°F.
Credit: Reviewed.com / Julia MacDougall
Each dishwasher testing station has an Intellifaucet that maintains the ingoing water temperature at around 120°F.

The dishwasher is connected to an Intellifaucet, which guarantees the recommended incoming hot water temperature of 120°F.

We level the dishwasher both in a side-to-side and in a back-to-front sense. The act of leveling may seem superfluous, but having a dishwasher installed on an angle could obstruct clean water flow and dirty water drainage. A dishwasher that’s not installed on the level might leak or its spray jets may miss some dishes. By leveling, we give each product the chance to perform at its best.

Lastly, we run a break-in cycle to check that the dishwasher is hooked up properly and that water is flowing through the machine ahead of subsequent tests.

Objective Testing

The main purpose of a dishwasher is, of course, to remove food and liquid detritus from your dishes. But how, exactly, do your dishes actually get clean? It turns out that the process of cleaning a plate in a dishwasher relies on the convergence of a few different factors: the type of food/liquid staining the plate, how long that stain has been on the dish, the dish’s placement within the dishwasher in general and the rack in particular, the detergent you choose, the amount and placement of other dishes in a load, and the dishwasher cycle and feature selections.

In our testing protocol, we account for all of these variables.

Dirty dishes with food stains being baked on.
Credit: Reviewed.com / Julia MacDougall
Stains are baked onto dishes in the oven at 170°F for 1 hour.

What goes into a dirty dishwasher? Dirty dishes! We need standard dirt on standard dishes to properly compare performance from machine to machine, however, so we must make all the food stains ourselves. We buy the same brand of ingredients and prepare the same Corelle dishes, applying food stains and then cooking them on—either from a short stint in the microwave or an hour in the oven at 170ºF. We then let the dishes sit in the dishwasher for no more than 48 hours. This entire process simulates dishes that have been used, left out, and then put into the dishwasher.

A plate is stained with meat.
Credit: Reviewed.com / Julia MacDougall
Test plates are stained with meat.

We test three cycles on each dishwasher, the Quick (or 1 Hour) cycle, the Normal Cycle, and the Heavy (sometimes called “Pots & Pans”) cycle. In each of these cycles, with the exception of the Heavy cycle, we create a load of dirty dishes containing 19 dishes – four glasses, four plates, three regular bowls, four small bowls, and four spoons, containing milk, meat, oatmeal, spinach, and egg stains, respectively.

A small bowl is stained with burnt cheese.
Credit: Reviewed.com / Julia MacDougall
Burnt cheese is one of the additional stains included in the Heavy Cycle.

Because the Heavy cycle is by definition a more intense wash cycle, we bake three additional food stains onto casserole dishes: burnt sugar, melted cheese, and leftover lasagna, which stand in for burnt-on carbohydrates, animal fats, and a mixture of the two, respectively.

Dishes in a dishwasher.
Credit: Reviewed.com / Julia MacDougall
Dish placement affects the dishwasher cleaning performance.

In our tests, we determine where to place dishes based on recommendations listed in the manufacturer’s use and care manual. These recommendations optimize the likelihood that strong jets of water will consistently strike the dish and remove difficult stains. If no mention of dish placement is made in the manual, then we abide by a general loading pattern that most closely matches those of other dishwashers in the same style and price range.

Dishes in a dishwasher.
Credit: Reviewed.com / Julia MacDougall
"Dummy" or "Ballast" dishes are interspersed with the stained dishes in each dishwashing cycle.

In loading the dishes, we alternate dirty dishes with “dummy” or “ballast” dishes, or clean dishes that are identical in type and style to the dirty dishes. This spreads out the dish load more, and helps us to more exactly determine how clean dishes can get at varied locations throughout the dishwasher.

A water carafe in the dishwasher.
Credit: Reviewed.com / Johnny Yu
Oddly-shaped or unusual dishes are analyzed qualitatively for drying.

Lastly, we also distribute a selection of oddly-shaped, large, or plastic items, such as baby bottles, water bottles, a water carafe, and Tupperware containers throughout the dishwasher (without blocking water jets to the main dish load). These dishes are not used to ascertain cleaning power, but are useful in describing the product’s drying capabilities, which will be discussed later.

Dishwasher cycle settings.
Credit: Reviewed.com / Johnny Yu
We select the default settings for the Quick, Normal, and Heavy (or Tough, in this case) cycles.

Since most users do not enable features when they wash dishes, we use the default settings on each of the Quick, Normal, and Heavy Cycles, and do not select any extra features, such as extra rinse or extra drying. This also allows us to compare each dishwasher at its default setting.

A dishwasher filter.
Credit: Reviewed.com / Julia MacDougall
Dishwasher filters are removed and cleaned between each dishwasher cycle.

Prior to each individual wash cycle, we add 24 g of Cascade powder detergent into the detergent dispenser. We also clean out the filter between each cycle run and remove any food or stain detritus that may have collected there during the course of the previous cycle. If any rinse aid samples have been provided along with the dishwasher test unit, we fill the rinse aid dispenser with those samples. If no samples are included, we fill the rinse aid dispenser up to the top with Cascade brand rinse aid.

Once a cycle is complete, we record the cycle time duration, water use, and electricity use. We wait an additional 30 minutes after the end of the cycle before unloading the dishes; this gives the dishes more time to air dry, and reduces the possibility of wet dishes on the upper rack dripping down onto dishes in the lower rack.

Drying

Once the 30-minute waiting period has elapsed, we open the dishwasher to assess the dryness of each dish, one by one. Dryness is judged on a scale of 1 to 3, defined by these three descriptions: soaking wet (it would be impossible to eat off of the dish), slightly wet (a few passes with a towel would make it completely dry), and bone dry (no water droplets present, and ready to eat off). The drying scores for each dish are used to calculate the overall drying score for that cycle.

We also note and describe the drying condition of the oddly-shaped, large, and plastic objects that were mentioned earlier, but we do not include these judgments in the score, since those results can vary greatly.

Stain Removal

A stained dish before and after a dishwasher cleaning cycle.
Credit: Reviewed.com / Johnny Yu
A stained dish before (left) and after (right) a dishwasher cleaning cycle.

After assessing the drying score for each dish, we determine exactly how much of the stain has been removed from each dish. We arrive at the stain removal percentage using a rough estimate of the surface area occupied by the stain before and after the wash cycle. Looking at the amount of stain left behind on individual dishes and the location of dirty dishes gives us a good idea of the cleaning power and water distribution in each cycle. The stain removal scores for each dish are used to calculate the overall stain removal score for that cycle.

Redeposit

Redeposit occurs when food stains from one dish have been washed onto another dish. Since redeposit is a measure of how well a dishwasher filters water, we score it separately.

Spinach redeposit on a glass.
Credit: Reviewed.com / Kyle Looney
Spinach redeposit can sometimes be found on other dishes.

In our dishwashing loads, the spinach stain is the most likely suspect in the case of redeposit. In fact, leafy greens tend to clog filters, which is why we use it. We have also observed some bits of meat on dishes other than the plates in the past.

We score redeposit on a 1 to 3 scale defined by these three descriptions: high amounts of redeposit (large portions of a new food stain exist on a dish), some redeposit (only a few dots of meat or spinach are found on another dish), and no redeposit (a dish is free of the stains from other dishes). The redeposit scores for each dish are used to calculate the overall redeposit score for that cycle.

Dirty Dish Scoring

In our testing, we define a “dirty dish” as a dish that still has remnants of that dish’s food stain and/or redeposit from another dish. In addition to calculating the stain removal for each dish, as discussed above, we also calculate the total number of dirty dishes (out of 19 dishes for the Normal and Quick Cycles, and 22 dishes for the Heavy Cycle).

Objective Test Scoring

We base four major scores on our objective testing: Efficiency, Quick Cycle, Normal Cycle, and Heavy Cycle.

A power meter measures the electricity usage of each dishwasher cycle.
Credit: Reviewed.com / Julia MacDougall
A power meter measures the electricity usage of each dishwasher cycle.

The efficiency score is based off of the water and power usage for each cycle, which we project into the average usage for a year. Lower water and power usages translate into a higher efficiency score.

The Quick, Normal, and Heavy Cycle scores include the drying, stain removal, dirty dishes, and redeposit scores discussed above, as well as the cycle duration. The exception is the Heavy Cycle, where we do not assess drying. This is largely because we have found that stain removal is the most important aspect of a customer’s choice to use a heavy cycle.

Sound

As dishwashers get quieter, consumers pay more attention to sound ratings, which are usually described in units of dBA (decibels with A-weighting). Decibels are logarithmic units of loudness; basically, for every doubling in loudness you perceive, the decibel level has increased by 6-10 dB.

Some manufacturers are making dishwashers that have sound ratings as low as 38-40 dBA, which is on par with the average amount of noise in a library.

Louder dishwashers have sound ratings between 50-55 dBA, which represents, at minimum, a dishwasher that sounds twice as loud as the quietest ones available on the market today; that kind of noise can be disruptive in an open concept living environment, and especially if you are having a conversation in the kitchen.

We do not test sound ratings ourselves, largely because it’s an extremely onerous and expensive task. We feel the installation of an anechoic chamber and hiring of an audio engineer would be overkill—especially since retailers already force an independent third party sound lab to test nearly every dishwasher. We incorporate that sound rating into the overall score for a given dishwasher.

Subjective Scoring

The other part of our dishwasher scoring involves recording the more intangible aspects of the user experience.

We judge ease of use (i.e. in changing cycles, in opening and closing the dishwasher door, etc.), the usefulness of certain features (i.e. a third rack, a cutlery basket that hangs on the edge of the rack, etc.), and the sturdiness of the materials (i.e. if the racks feel rickety, etc.). With these scores, we can give you details about our personal experiences with a given dishwasher that cannot be described by objective tests.

These are more difficult to score, but we think we’ve done a good job developing a questionnaire that teases out differentiation without highlighting personal biases. In fact, we’re proud that multiple reviewers come to the same conclusions after reviewing the same unit using our questionnaire.

By combining both objective dishwasher testing and experience-driven data, we help our readers make an informed decision when the time comes to purchase a new dishwasher. To see the results of these subjective and objective test protocols, be sure to look at our list of dishwasher reviews. If you want to see our current top ranking dishwashers are, check out the Best Right Now: Dishwashers article.