Because undercounter warewashers incorporate a number of variables, including electricity, water and chemicals, operators need to carefully weigh their options when specifying these units. 

Rack flow: This will determine how many racks per hour can be cleaned, 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. The number of pieces in a place setting, including glassware, plates, salad plates, bowls and silverware, multiplied by the number of seats will determine the approximate load. The table turns also need to be taken into account. This means with two seatings a night, there will be a total of 500 pieces to wash.

Sizing: A common error operators make is purchasing an undercounter unit when a door machine is needed. An important factor to consider is that warewashers typically only meet about 70 percent of the hourly rack rates, because these numbers are based on a perfect scenario, without taking into account the employees' work speed or other contributing factors. Operators can count on losing about 12 racks per hour due to the realities presented by working in a wet, and typically hectic, dishroom.

Utility compatibility: Oftentimes, 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 temperature: When purchasing an undercounter warewasher, operators need to assess their incoming water temperature. Cooler water sources may require a booster heater to maximize the machine's performance. This is because the colder the water used, the longer the wash cycle will be. An extended wash cycle will result in reduced washing capacities.

Water condition: Prior to specifying a machine, it may be worthwhile to assess the water condition to determine if a mineral filtration system is needed. The key to low-cost operation in dishwashing is how clean the wash water is kept. Cleaner water requires fewer chemicals for sanitizing. There are units available that provide advanced screening mechanisms that effectively wash 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.