Does a restaurant need a booster heater for a 180 F final rinse?

A high-temperature machine kills germs with heat. The final rinse has to land on the dishes hot enough to bring their surface to a sanitizing temperature. The FDA Food Code explains that "the surface temperature must reach at least 71ºC (160ºF) as measured by an irreversible registering temperature measuring device." To get there, the rinse water has to enter the machine's manifold at 180 degrees F for most machines, or 165 degrees F for a stationary rack, single temperature machine. Section 4-501.112 sets the ceiling: the rinse "may not be more than 90oC (194oF)."

The main water heater cannot do this on its own. The county's guide says a restaurant water heater runs at a thermostat set-point of at least 120 degrees F, and it requires a 140 degrees F feed for a high-temperature machine. Running the whole building at 180 degrees F would be a scald risk at every sink. A booster heater solves that. It only heats the water going to the machine's final rinse.

### The county's booster rule

The guide states the rule in three sentences:

• "A booster heater shall be provided when a high temperature warewashing machine is installed to pre-heat the water."
• "A minimum incoming fresh hot water supply of 140°F is required for high-temperature dishwashing machines."
• The booster raises that supply "up 40ºF to attain the required 180ºF at the manifold for the final sanitizing rinse cycle."

The guide defines a booster heater as "a tankless water heater designed and intended to raise the temperature of hot water to a higher temperature for a specific purpose." So it is not a substitute for the main heater. It needs a 140 degrees F feed to work with.

Two more county requirements affect the plumbing around the booster.

1. 1A temperature reading. The guide says the machine must have a device that shows the water temperature "when the water enters the hot water sanitizing final rinse manifold," and a data plate listing the temperatures and pressures the manufacturer requires. The Food Code adds that such a device must read "in each wash and rinse tank."
2. 2A pressure reading. The final rinse pressure must be "not less than 15 psi nor more than 25 psi," with 20 psi as the optimum. The guide explains why: low pressure gives "inadequate spray patterns and incomplete coverage." High pressure "will tend to atomize the water droplets" into a vapor that cools before it reaches the dishes. A machine that lists a pressure on its data plate needs a gauge, and the guide asks for a pressure regulator on the final rinse line.

The wash tank has its own number. The guide says that in a machine using hot water to sanitize, "the wash solution temperature must be at least 150°F," and 150 to 165 degrees F "for effective washing." That comes from the main heater or from the machine's tank heater, not from the booster.

Where the booster goes matters as much as its size. The guide says the booster must be "properly sized to meet the demand of the final sanitizing rinse cycle of the warewashing machine," and gives these installation rules:

• Stay close. Provide a hot water line directly from a dedicated primary heater, "or a booster heater shall be provided within 5 feet of the warewashing machine to avoid heat loss in the supply lines."
• If it is farther than 5 feet, the final rinse line "shall be either recirculated or equipped with approved self-regulating heat tape."
• Keep it off the floor. A booster installed below a drain board must be "at least 6 inches above the floor and away from walls," so it can be cleaned and serviced.
• Add a gauge. A temperature gauge is required on the supply line "just before the booster heater."
• Temper the rest. A thermostatic mixing valve goes on any line that carries hot water to other appliances or fixtures.

### Backflow and drains

The guide says warewashing machines and hot water equipment "may require the installation of approved backflow protection," and that annual test results "shall be maintained on file." Where the machine drains is a separate question. Our page on whether a commercial dishwasher can drain to a grease trap covers that.

A low-temperature machine sanitizes with a chemical, usually chlorine. The county's guide says the wash in that kind of machine "may not be less than 120ºF," and that a machine using chemicals must have "an approved device that indicates audibly or visually when the sanitizer level is low." The plan review checklist repeats the alarm requirement for a mechanical sanitizer dishwasher. No 180 degrees F rinse is involved, so no booster is required.

The trade-off is chemistry and upkeep. A chemical machine needs sanitizer on hand, test strips and a working alarm. A high-temperature machine needs the booster, more gas or electric load, and a clean supply line. That choice is usually made by the kitchen and the equipment dealer, and the plumbing has to match it.

A water heater that serves a machine also has to be big enough. The plan review checklist says a restaurant with a mechanical dishwasher needs a water heater of at least 75 gallons with a 100 percent recovery rate. Our page on how to size a commercial water heater for a Maricopa County restaurant shows how that number is figured.

These are the problems a plumber runs into most often on a hot-water-sanitizing line.

1. 1Rinse never reaches 180 degrees F. Check the incoming temperature first. If the main heater is set at 120 degrees F, the booster is being asked to add 60 degrees F instead of 40.
2. 2Pressure swings. A missing regulator or a worn one moves the rinse outside 15 to 25 psi. That is a plumbing fix, not a machine repair.
3. 3Long run, cold rinse. If the booster sits more than 5 feet from the machine, the line loses heat between the two. Recirculation or heat tape is the county's fix.
4. 4Scale. Hard water scales heating elements, and Phoenix water is very hard. The county guide says to consider "water filters and/or softeners." Our page on whether hard water ruins a hot water heater covers what scale does to heating equipment.
5. 5No clean dishes to sanitize. The guide says "unless utensils are clean to sight and touch, they cannot be effectively sanitized," so a weak wash cycle defeats a good booster.

### What to do next

Start with the machine's data plate. It lists the temperatures and pressures the manufacturer requires, and those decide the booster size. Then measure the incoming water where it reaches the booster and read the gauges on the final rinse line. Ask your plan reviewer to confirm the numbers for your machine, since the county needs to approve the plan.

HQ Plumbing & Air is licensed and insured, and can look at the piping around a dish machine and tell you what would need to change. We offer free estimates and upfront pricing.