9.3 Water Temperatures, Scald Control & Thermal Expansion

9.3 Water Temperatures, Scald Control & Thermal Expansion

Quick Answer: Occupied buildings get hot water to bathing, washing, culinary, laundry, and maintenance fixtures (248 CMR 10.14(5)). Residential stored domestic hot water is 120–130°F (130°F is the cap; dishwashers and dispensers that need hotter water are excepted). Shower valves and tub fillers are 120°F / 120°F. Public and employee lavatories are 120°F maximum in both 10.14 and 10.10(10)(a). Commercial-kitchen hand sinks are 120°F / 120°F in the 10.14 table; the Board policy on the Mass.gov list allows 120°F there and does not treat the kitchen hand sink as a “public” lavatory. Shower controls are Product-accepted thermostatic, pressure-balancing, or combination valves, limited to 120°F and field-adjusted before final. ASSE 1070 is named for central shower mixing used in lieu of individual 1070 controls and for free-standing tubs and whirlpools. When a meter check, PRV, or backflow preventer closes the system, add a properly sized expansion tank close to the metering device — and never put a check valve in the heater cold.

This is the temperature third of the PSI six-item Water Supply cluster. Independent OpenExamPrep teaching uses 248 CMR 10.14(5) and 10.10, plus the Mass.gov Maximum Temperature for Hand Sinks in Commercial Kitchens policy still posted on the Board policies list.

The 10.14 temperature table — numbers you can defend

10.14(5)(c) caps domestic hot water in residential buildings at 130°F. Fixtures that need higher temperature for proper function, such as dishwashers and hot-water dispensers, are excepted. The same subsection prints Minimum and Maximum Hot Water Temperatures (Fahrenheit):

*See 10.14(5)(c) for the dishwasher/dispenser exception.

248 CMR 10.10(10) matches the lavatory split: public and employee maximum 120°F, flow 0.5 GPM (metering faucets 0.25 gallons per cycle); residential maximum 130°F. 10.10(4)(c) is the shower-control rule: every shower-head supply goes through a Product-accepted individual thermostatic, pressure-balancing, or combination thermostatic/pressure-balancing valve. Hand-held showers follow the same rule, count as a shower head, and need a vacuum breaker. Shower heads 2.0 GPM maximum. All control valves shall limit mixed outlet temperature to 120°F and shall be adjusted by the installing plumber prior to final inspection under 248 CMR 10.04(2)(b).

ASSE 1070 appears by name in two 10.10 places. Central automatic temperature-control mixing valves may be used in lieu of individual control complying with ASSE 1070, if they limit hot water to individual shower controls to 120°F whenever showers are in use. Those central valves need a thermometer in the outlet piping and check valves on hot and cold inlets. When that central valve already limits the incoming hot, individual shower controls may be Product-accepted two-handle or single-handle valves. Free-standing tubs and whirlpool baths shall not exceed 120°F, controlled by a temperature-limiting device conforming to ASSE 1070. 10.10 does not print “ASSE 1016” as the shower-valve standard number; it prints the thermostatic / pressure-balancing / combination function and Product acceptance. Teach what Massachusetts printed.

Commercial-kitchen hand sinks. The 12/8/2023 table already lists 120 / 120. The Board policy Maximum Temperature for Hand Sinks in Commercial Kitchens (enacted 10-02-2013, still on the policies list) interprets older public-lavatory language: commercial kitchens are not “public,” so those hand sinks were not forced to the old 110°F public-lavatory outlet limit, and the Board allows a maximum of 120°F. Do not walk into PSI quoting 110°F for a kitchen hand sink. Current 10.10 public lavatories are 120°F, and kitchen hand sinks are 120°F in both the table and the policy. Scullery and service sinks may run to 140°F; that is a different row from the hand sink.

Scenario. A Framingham restaurant has a 140°F pot sink beside a hand sink. The pot/scullery row allows 140°F. The hand sink stays at 120°F maximum. The public restroom lavatory is also 120°F, 0.5 GPM. The dish machine that needs hotter sanitizing water is the kind of fixture 10.14(5)(c) excepts from the residential 130°F stored-water cap when higher temperature is required for function — still protect that machine’s water supply under 10.14(7) and Table 10 (dishwasher C-L six inches above flood level on hot and cold).

Hot-water recirculation: if developed length from the source (water heater or recirculation loop) to the farthest fixture supply exceeds 75 feet, the system shall be total return circulation. Minimum recirculating line 1/2 inch (10.14(2)(f)).

Combination potable water / space-heating systems (10.14(6)(g)) add their own temperature and expansion hardware: maximum 100 feet developed length heater-to-coil-and-back, Product-accepted 10.06 piping, a pump timer at least once every six hours for 60 seconds, a properly sized potable expansion tank, and a mixing valve for service to the plumbing fixtures.

Thermal expansion when the system is closed

Two 10.14 sentences must be read together.

10.14(6)(c): A check valve shall not be installed in the cold-water supply to any hot water heater or hot water storage tank. A properly sized thermal expansion tank may be installed to prevent excessive pressure from thermal expansion.

10.14(3)(j): When a metering device with a check valve or backflow preventer is installed, creating a closed system, a properly sized thermal expansion tank shall be installed as close as possible to the metering device.

A PRV that holds house pressure at 80 PSIG (10.14(2)(e)) also stops expanded water from pushing back toward the street. Treat that closed-system physics the same way 10.14(3)(j) treats a meter check: the water heater still expands, and the expansion tank is the listed relief path — not a check on the heater cold that 10.14(6)(c) forbids. Combination space-heating loops shall have a properly sized potable expansion tank (10.14(6)(g)4.).

Place the tank where the code puts it: as close as possible to the metering device when the meter (or its backflow preventer) is what closed the system. Size it to the heater volume and the temperature rise using the tank manufacturer’s listing; 248 CMR does not print a gallon table for expansion tanks, so do not invent one.

10.05(7)(e) separately requires protection of piping against thermal expansion as temperature variation warrants. That is pipe-loop expansion (especially plastics), not a substitute for the potable expansion tank on a closed water heater.

Unattended basement storage connected to a direct heating device needs fully automatic control so tank water cannot reach 212°F (10.14(6)(d)2.). Coils or boosters shall not sit in direct contact with a building heating unit’s heat-generating source (10.14(6)(d)1.).

Water hammer arrestors

248 CMR 10.14(2)(b) (Prevent Water Hammer): building water-supply systems that have quick-acting / quick-closing valves and solenoid valves shall have devices to absorb the high pressures from those valves. Devices are air chambers that include a means for restoring the air if they waterlog, or other Product-accepted mechanical devices. Place them as close as possible to the quick-acting valves and keep them accessible for maintenance or replacement. A mechanical absorber may also be installed at the ends of long runs or on piping serving a battery of fixtures. Follow the mechanical-device manufacturer on location and method.

Clothes washers, dishwashers, and flushometers are the usual solenoid or quick-close loads. A waterlogged air chamber with no recharge path is not the device 10.14 described. Accessibility is part of the listing: an arrestor buried behind tile with no access is not maintainable.

Scenario. A Cambridge two-family gets a new meter with an integral check. The water heater cannot receive a check on the cold. Install a listed potable expansion tank as close as possible to that meter, keep shower valves at 120°F after you set them, and put a Product-accepted mechanical arrestor (or a rechargeable air chamber) next to the washing-machine solenoid valves, accessible.

Official resources

• 248 CMR 10.14 (Cornell) — 10.14(5) temperature table, 10.14(2)(b) water hammer, 10.14(3)(j) and 10.14(6)(c) expansion
• 248 CMR 10.10 Plumbing Fixtures (Cornell) — shower mixing, ASSE 1070, lavatory 120°F / 130°F
• Maximum Temperature for Hand Sinks in Commercial Kitchens — Board allows 120°F; kitchens are not “public”
• Policies, regulations, and statutes for plumbers and gas fitters