Spec Check: Undercounter Warewashers

Undercounter warewashers are typically one of the most expensive equipment pieces in a commercial kitchen and usually one of the most abused. Though compact and geared for smaller operations, these units can be complicated. Because these warewashers incorporate a number of variables, including electricity, water and chemicals, specifying the appropriate unit is key to ensuring dishware is properly cleaned and sanitized. 

 Operators first need to consider what type of items they plan to wash in these units, including glassware, dishes or a combination of both. This will help determine whether a low- or high-temp unit is necessary. Low-temp warewashers utilize water that is at 120 degrees F., while also incorporating chemicals for proper sanitizing. High-temp warewashers typically heat the water to 150 degrees F. for washing and 180 degrees F. for sanitizing.

In comparing the two types of units, low-temp machines only require 120 volts of power, but dishes come out wet. High-temp units require 220 volts to operate. With these units, dishes come out hot and, therefore, dry more quickly.

Another consideration operators need to weigh is the location of the unit. For undercounter warewashers used in the front of house or behind a bar, low-temp units are a more common choice due to the lack of hot steam escaping from the machine, which can create uncomfortable conditions for the user and patrons. Also, this type of warewasher provides cooler glass temperatures after washing, which better accommodate cold beverages.

Although glassware dries more quickly with fewer spots when washed in high-temp units, there can potentially be a smaller yield from a keg by dispensing beer, for example, into a warm mug or glass due to foaming and other considerations. On the plus side, high-temp warewashers are more effective at breaking down solids and fats on glasses, dishware and flatware, including lipstick marks and finger smudges.

Waste management in terms of food scraping is another concern when specifying these units. Will staff scrape leftovers into garbage cans or disposers by hand or will they employ another method? Understanding this helps determine the work flow and, subsequently, the best placement for the undercounter warewashing unit.

It is important to note that, unlike residential dishwashers, commercial warewashers don't have top racks. Undercounter warewashers typically accommodate one rack at a time. During the cycle, staff remove the rack after cleaning and then load in a different rack containing dirty dishware and glasses.

When specifying an undercounter warewasher, a common mistake operators make is not allowing adequate space to stage and unload racks. More labor is required for undercounter units than door-type machines, so the dishwashing area needs to be taken into account.

When looking at the warewasher's placement, understand the unit's drainage needs. For lower level or basement locations as well as older facilities, drains may be situated in the wall as opposed to on the floor. Although approximately 80 percent of warewashers utilize gravity drain systems, pump drains are necessary for drains that are more than eight inches off of the floor.

Rack flow will determine how many racks per hour the unit can clean, which ties into the amount of seats in the operation. Although undercounter warewashers have standard sizing, units have capacities ranging from 18 to 40 racks per hour. To determine the approximate load, multiply the number of pieces in a place setting, including glassware, plates, salad plates, bowls and silverware, by the number of seats. For example, if a 50-seat restaurant has 5 pieces of ware per setting, the warewasher will need to accommodate 250 pieces per load. The table turns also need to be taken into account. This means with 2 seatings a night, there will be a total of 500 pieces to wash.

Another common error operators make is purchasing an undercounter unit when a door machine would be the better option. An important factor to consider is that warewashers typically only meet about 70 percent of the hourly rack rates, because factories base these numbers on a perfect scenario. Rack rates do not take into account the loading speed of employees and other factors. As a result, operators can count on losing about 12 racks per hour due to the realities presented by working in a wet, and typically hectic, dishroom.

Many operators don't realize that standard hot water heaters and pipes are not sufficient for these units. This can cause problems with machines reaching the proper wash temperatures and water pressure. Because commercial undercounter dishwashers require a substantial hot water supply, it is important to confirm that the size of the pipe connecting to the unit is large enough to provide an adequate amount of pressure. Water pressure should be between 20 and 30 pounds per square inch (PSI) at a temperature of at least 120 degrees F.

When purchasing an undercounter warewasher, the incoming water temperature needs to be assessed. Cooler water sources may require a heat booster to provide adequate water temperatures and help maximize the machine's performance. The colder the water used, the longer the wash cycle will be. This extended wash cycle will result in reduced washing capacities, which could be decreased by as much as 50 percent, depending on the water temperature. Boosters range from 2 to 9 kW, depending on the warewasher's make and model.

Undercounter warewashers require between 20 and 60 amp breakers, so operators need to confirm they have adequately sized breakers. In some cases, electricians may need to run dedicated lines to the unit. High-temp units run off of a minimum of 220 volts and have a more substantial amp draw than low-temp machines.

Plate buildup can be a result of impurities in the water or excessive amounts of mineral content. The key to low cost operation in dishwashing is how clean the wash water is kept. Prior to specifying a machine, it may be worthwhile to assess the water condition to determine if a mineral filtration system is needed. (For more on water filtration's impact on foodservice equipment, turn to page 102.) Cleaner water requires fewer chemicals for sanitizing. Some units provide advanced screening mechanisms, which effectively cleanse the wash water by incorporating a level of filtration. This keeps contaminates at lower levels and can produce more effective cleaning results. Warewashers with internal filtration units use less water overall.

Units with different operating principles are available, depending on the operator's preference. Fill and drain machines are available in partial and complete variations. With complete fill and drain machines, 100 percent of the rinse water drains out upon completion of the wash cycle. The tank only contains water during the wash cycle. Partial fill and drain units use 100 percent of the wash water and drain 100 percent of it, then bring in the rinse water before sanitizing. The machine uses the rinse water during the next wash cycle. These types of units are geared for operations washing heavily soiled items. In addition to fill and drain warewashers, overflow units are available. With these types, the wash water is reused cycle after cycle, but fresh water is utilized for rinsing. The operator breaks the cycle by powering down and draining the unit. Overflow warewashers are utilized with less soiled items, such as glassware.

Operators can choose from different finishes that will help repel lime deposits in warewashing units. Also, depending on the brand, there may be the option of either composite or stainless steel wash and rinse arms.

Energy Star certification criteria for undercounter warewashers has been updated. High-temp units are required to have idle energy rates of less than 0.50 kW and water consumption of less than .86 gallons per rack. For low-temp Energy Star machines, the idle energy rate is less than .50 kW and water consumption is less than 1.19 gallons per rack.

Typical undercounter machines wash at 10 PSI for 90 seconds for a general wash. There are units that offer multiple settings for different run times, although this is not typical with a majority of commercial dishwashers. This offers a choice of washing at 7 PSI for 90 seconds, 10 PSI for 120 seconds or 15 PSI for two minutes. The varied time selection allows the adjustment to the type of ware or amount of soil. For example, shorter run times may be preferable for operations washing delicate items. Variable speed units also are available for operators to choose the length of the wash time and water pressure.