Low-Temp vs. High-Temp Commercial Dishwashers
The NSF and local governments have very strict guidelines on sanitization in commercial warewashers, requiring either extreme heat or sanitizing chemicals to remove bacteria from dirty dishes, cookware, and utensils. These guidelines have resulted in two main types of dishwashers: high temperature, which use an often-external booster heater to heat water to a sanitizing temperature, and low temperature, which use chemicals to sterilize the dishes. Both methods remove bacteria, but the differences in how they do so can have an impact on which one is best suited to your operation.
Comparing Commercial Dishwashers
As mentioned above, NSF sanitation guidelines ensure that both high temperature and chemical sanitizing methods remove bacteria from dishes. Customers cannot see germs, though; they are more interested in what meets the eye, and sometimes low-temperature dishwashers are not able to completely remove lipstick, greasy residue, and other hard-to-remove substances in just one wash. Fats and grease can represent a particular difficulty, as temperatures below 130 degrees Fahrenheit cannot effectively remove them. High-temperature washers must reach a minimum of 180 degrees Fahrenheit, which means they remove these difficult substances much more reliably.
Both types of dishwashers have varying impacts on the environment and your utility bills, with some pros and cons for each. Because high-temperature warewashers must use a powerful booster heater to get wash water to the proper temperature, this type will typically use more energy, in the form of either gas or electricity, than a low-temperature washer. It may also be necessary to install a cold water line to the unit's drain to "quench" or "temper" drain water, cooling it from sanitizing temperatures to a level that is safe for wastewater systems and grease traps. In contrast, low-temp machines are more energy efficient, but the cost of sanitizing chemical refills every week or so can be pricey.
The location of your dishwasher can play a big role in determining whether high temp or low temp will work best for you. High-temperature machines produce more steam, so most models require a vent hood system. That unit will capture the steam output in order to prevent water damage to the surrounding area and keep all that excess heat from creating an uncomfortable work environment. Because of this, a high temperature machine may require more room and an additional electrical connection, not to mention the potential for a sizable bill for the hood.
Some specialty models have built-in condensers or other ways of mitigating the steam created by the hot water. They typically use the steam to heat incoming wash water for the next cycle, which cuts the energy needs for that process. As it does that, the steam condenses on the fresh water pipes and is dispersed down the drain.
Because they lack that steam and the potential to create higher ambient heat, low-temperature machines are usually preferred for locations near customers. They don't produce as much steam because they don't have to heat the water to sanitizing temperatures, which also means they're easier on your utility bills.
Different models will have varying utility requirements. With the dishwasher, booster, and vent hood, high temperature washers usually require more power, and some models may only be available in with a 220 volt or a 3-phase configuration. Machines that use chemical sanitizers will normally require fewer amps. For high-temperature dishwashers, the temperature of the incoming water is also a consideration; each booster is rated for how many degrees it can add to incoming water. For example, water that arrives at 110 degrees Fahrenheit will require a minimum of a 70-degree-rise booster to get to the required 180 degree minimum, while you will only need a 40-degree-rise booster if your water comes in at 140 degrees.
Dishwashers that use chemicals to sanitize must use a solution of chlorine, iodine, or ammonium. Unfortunately, these solutions can damage some materials used for dishes and utensils, such as some plastics, steel, silver, aluminum, pewter, and other alloys. If you are considering a low-temperature dishwasher, it will be important to know what all of your serving products are made of to avoid chemical degradation. Consult with your chemical vendor to make sure it’s safe to use its product with your wares.
For high-volume operations, wash cycle time is important to be aware of, as even a few seconds per wash can add up over the course of a dinner service. Because they do not have an extra rinse with chemicals at the end, high-temperature machines tend to have faster wash cycles on average. The hot water they are rinsed with means they also tend to dry faster and are ready to use sooner.
However, when this type is used for drinks and particularly in bars, remember you'll have to allow time for your drinkware to cool after washing, since hot glasses can warm up cold beers and blended cocktails. On the other hand, chemically sanitized glasses can prevent beer from forming a head, which will cut into the flavor profile and will force you to serve more beer to fill each glass, cutting into profits.
Regularly-scheduled fill-ups and maintenance will be required for any chemical sanitization dishwasher, as it cannot function without the chemicals its final rinse depends on. Most modern machines come equipped with a chemical dispenser that will need to be refilled on a weekly or monthly basis. While the high-temperature dishwasher may not require such regular attention, the necessity of the vent hood and booster mean there are two more major parts with the possibility of eventual failure, which could require emergency maintenance.
Costs of the Dishwasher Types
Upfront costs are easy to determine between the two types, since they're on the invoice. Low-temperature washers are generally going to cost several thousand dollars less than high-temperature washers.
Long-term costs are unfortunately not as easy to pin down. Low-temperature washers will have the ongoing costs of the chemicals, leaving you at the chemical manufacturer’s mercy if it decides to raise its prices. High-temperature washers require only detergent, but they also use more energy and water. Depending on the efficiency of the specific dishwasher, this may or may not outweigh the costs of the sanitizing chemicals, but low-temperature dishwashers are generally accepted to be more expensive over time, even with their lower initial cost.