Phoenix and Mesa both bar wastewater hotter than 150 degrees Fahrenheit from the city sewer, and neither lets heat push the treatment plant intake above 104 degrees. Piping that will carry wastewater above 140 degrees must be rated for it under the 2024 plumbing code. Hot kitchen equipment is usually cooled or tempered first.
What is the sewer temperature limit in Phoenix?
Phoenix City Code 28-8 makes it unlawful for any user to discharge to the city's treatment system "Water with a temperature greater than 150 degrees Fahrenheit (66 degrees centigrade) or heat in amounts that will inhibit biological activity in the POTW resulting in interference, but in no event heat in such quantities that the temperature at the headworks of the wastewater treatment plant exceeds 104 degrees Fahrenheit (40 degrees centigrade)." The headworks is where sewage enters the plant. The 104 degree figure is the one that governs when many hot discharges add up.
What is it in Mesa?
The same two numbers. Mesa's sewer code, Section 8-4-15, bars "Wastewater with a temperature greater than one hundred fifty degrees Fahrenheit (150°F) or heat in amounts which will inhibit biological activity in the POTW resulting in interference; but in no event, heat in such quantities that the temperature at the headworks of the POTW exceeds one hundred four degrees Fahrenheit (104°F)." Both cities track a federal pretreatment rule. 40 CFR 403.5(b)(5) prohibits "Heat in amounts which will inhibit biological activity in the POTW resulting in Interference, but in no case heat in such quantities that the temperature at the POTW Treatment Plant exceeds 40 °C (104 °F)," unless the approval authority allows other limits.
These are limits on the wastewater. They do not say where in your building the temperature is measured. If a hot stream joins a larger cool flow before it leaves the property, the mixed temperature is what leaves. That is a design question to settle with your plumber and the city's pretreatment staff, not something to assume.
Which kitchen equipment discharges hot water?
Steam kettles, steamers, boilers, dish machines and process tanks are the usual suspects. The plumbing code treats several of these as indirect waste. Section 802.1.5 of the Phoenix 2024 IPC says that where "devices and equipment such as process tanks, filters, drips and boilers discharge nonpotable water to the building drainage system, the discharge shall be through an indirect waste pipe by means of an air break or an air gap." Our page on commercial sinks and air gaps covers how that receptor works.
We did not find a rule in the city or county text that names dish machines or kettles, so do not assume your equipment is exempt or banned. Read the equipment's installation sheet for its drain temperature, then compare it to the city's limit.
What temperature must the drain piping handle?
Section 702.5 of the Phoenix 2024 IPC says "Where the wastewater temperature will be greater than 140°F (60°C), the sanitary drainage piping material shall be rated for the highest temperature of the wastewater." That is a piping rule, separate from the sewer limit. A discharge can be under 150 and still above 140, so the pipe material matters. Ask your plumber what the drain line is made of and what it is rated for.
How do kitchens cope with hot discharges?
By cooling or tempering the flow before it leaves the building, or by routing it so it mixes with cooler water first. Which method fits depends on the equipment and the flow. For dishwashers the final rinse water is hot on purpose; see whether a restaurant needs a booster heater for the 180 degree rinse. For steamers, see boilerless versus boiler-based commercial steamer plumbing, which covers the drain side.
What to do
- 1List every piece of equipment that drains hot water and find its rated drain temperature on the spec sheet.
- 2Compare it to 150 degrees Fahrenheit and ask the city's pretreatment staff how they want it measured or tempered.
- 3Confirm the drain piping is rated for anything above 140 degrees.
- 4Put the equipment spec sheets in the plan set; see why spec sheets matter at plan review.
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