To help determine what size dishwashing machine you will need, you must first determine how many racks of dishes per hour you will generate. Here's an equation that may help:
(# of pieces per person) X (# of persons per hour)
20 pieces per rack
When thinking about changing to low-temp warewashing from high-temp, remember that you will still need 140° water. Heating water in your hot water heater is less efficient than using a booster heater. Also remember that the chemical usage is directly proportional to the water the dishwasher uses, and most low-temp units use a great deal of water. High-temp is still the most efficient and productive means of warewashing.
Nationwide, health inspectors require that dish machine rinse temperatures be verified to reach between 170° - 212° F, the range sure to kill bacteria. You must use a mercury filled thermometer to hold the highest temperature reached.