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)."

Maricopa County’s general hot-fed arrangement uses a main water heater and a booster to reach the required rinse conditions without sending that sanitizing temperature to every sink. Its guide describes a thermostat set-point of at least 120 degrees F and a 140 degrees F feed for high-temperature warewashing. Confirm the accepted arrangement for the exact machine; Hobart’s LXGnR instructions instead identify a cold inlet and an internal booster. Do not substitute the general feed figure for that model’s instructions or assume the model has already been accepted by the County.

### 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." Its 140 degrees F feed describes that general hot-fed approach. It is not the inlet requirement for every internal-booster or heat-recovery machine. Submit the selected specifications to the County and resolve the approved model’s actual supply and heating arrangement before installation.

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 where applicable. The guide describes 15 to 25 psi, with 20 psi as optimum, for the fresh hot-water sanitizing rinse arrangement. It explains that low pressure gives "inadequate spray patterns and incomplete coverage," while high pressure "will tend to atomize the water droplets." Its pressure-gauge provision explicitly excludes machines using only a pumped or recirculating sanitizing rinse; its fill-and-dump example needs neither a pressure-reducing valve nor a pressure gauge for that pumped rinse. Hobart’s December 2024 LXn/LXGn manual likewise says all covered models have a pumped rinse, so a rinse-pressure gauge is not required or supplied. Compare the exact machine’s inlet flowing-pressure requirements separately; do not apply a line-pressure rinse specification to its inlet by assumption.

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.

Before reusing a supply for a replacement bar machine, check the heat-recovery glasswasher inlet review. It compares named cold-fed and hot-fed models and the manufacturer documents to submit for local review; a sanitizing temperature does not identify the required inlet by itself.

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 examples concern the guide’s hot-fed booster arrangement. Use the actual manufacturer’s troubleshooting instructions for a machine with a different supply or an internal heat-recovery system.

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 outside the applicable requirement. On a line-pressure rinse arrangement, check the data plate and the required rinse-pressure controls. On a pumped-rinse model, compare inlet flowing pressure with the manufacturer’s separate supply requirement; do not assume the 15 to 25 psi rinse figure or a rinse-gauge requirement applies.
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 and current instructions. Confirm the required inlet temperature, heating arrangement and pressure conditions for that model. Have the responsible provider check the incoming water and any required rinse readings; a pumped-rinse unit may not require a rinse-pressure gauge. Ask your plan reviewer to confirm the arrangement 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.

Hot rinse water also has a sewer-side limit; see how hot restaurant wastewater can be.