5.4 Water Heaters, Relief Valves, Hot Water Delivery & Temperature Control
Key Takeaways
Combination T&P relief valves must have a temperature steam rating at least equal to the heater's BTU/hour input, with the sensor in the top 6 inches of the tank and no valve between.
A relief valve discharge pipe must be full size, untrapped, unvalved, unthreaded at the end, and terminate within 6 inches of (but at least 2 pipe diameters above) the floor or receptor in the same room.
If hot water piping exceeds 100 feet of developed length to a fixture, a circulation system or self-regulating heat cable is required, with no more than 25 feet uncirculated.
A public lavatory may be no more than 8 ounces of water from the hot water source, or within the pipe lengths in Table 382.40-1d (for example 6 feet of 1/2-inch pipe).
Showers in public buildings need ASSE 1016 pressure-balanced, thermostatic or combination mixing valves; lavatory and sink temperature-limiting valves meet ASSE 1070.
Where hot water is required (SPS 382.40 (3) (b))
Hot water must be provided to all fixtures, appliances and equipment used for personal washing, culinary purposes or laundering, and to maintenance sinks in public buildings. Lavatories, wash fountains and showers outside dwelling or living units must receive tempered or hot water. Exceptions: lavatories in park shelters and bath houses that are closed November 15 to March 15 and are not places of employment, and wayside lavatories that are not places of employment.
Temperature maintenance (SPS 382.40 (5) (b) and (bm))
| Situation | Requirement |
|---|---|
| Hot water developed length from source to a fixture exceeds 100 feet | Circulation system or self-regulating electric heating cable |
| Circulation used | No uncirculated branch longer than 25 feet |
| Heat cable used | Cable reaches within 25 feet of each fixture |
| Insulation on circulated or traced pipe | Heat loss no more than 25 BTU/h per sq ft aboveground, 35 underground |
Traced piping must be identified as electrically traced, and the cable may be subcontracted. Circulation connections go downstream of the heater's control valve.
Public lavatories in public buildings must meet one of two tests measured from the nearest hot water source, which can be a heater, a circulation loop or a heat-traced line:
- Maximum length from Table 382.40-1d: 1/4 inch = 24 ft; 3/8 inch = 12.5 ft; 1/2 inch = 6 ft; 5/8 inch = 4 ft; 3/4 inch = 2 ft; 7/8 inch and larger = 0.5 ft. Other fixtures and appliances are allowed 25 ft at any size.
- Maximum volume of 8 ounces in the piping (not counting stop valves, flexible connectors or the faucet), using the ounces-per-foot values in Table 382.40-1h.
Water heater safety devices (SPS 382.40 (5) (d))
- Every pressurized storage-type heater and unfired hot water storage tank needs one or more combination temperature and pressure (T&P) relief valves. The valve's temperature steam rating (AGA rating) must equal or exceed the heater's BTU per hour input. No shutoff valve or restriction may be installed between the heater and the valve.
- Pressurized non-storage (instantaneous) heaters need a pressure relief valve at the hot outlet, also with no shutoff between.
- The T&P sensing element must extend into the tank and monitor the top 6 inches.
- A vacuum relief valve is required when the bottom of the heater or tank is more than 20 feet above any outlet it serves.
Discharge piping
| Rule | Requirement |
|---|---|
| Material | Acceptable water distribution material under SPS 384.30 (4) (e) 1. |
| Size | Not smaller than the relief valve outlet |
| Trap | Not trapped |
| Valves | None allowed |
| Termination | Gravity drain to a floor served by a floor drain, or to a receptor |
| Height of outlet | Within 6 inches of the floor or receptor, but not less than 2 x the pipe diameter |
| End | Not threaded |
| Location | In the same room or enclosure as the heater |
Worked example. A 3/4-inch T&P discharge pipe must end no more than 6 inches above the floor drain area and no closer than 1-1/2 inches (2 x 3/4 inch). Ending it 8 inches up, adding a ball valve for service, or threading the end would each be a violation.
Controls (SPS 382.40 (5) (e))
Every hot water system needs automatic temperature controls adjustable across the intended range, and a separate means to cut off energy to each heater and each circulation system. Water heaters themselves must meet SPS 384.20 (5) (p). Their venting, enclosures and energy rules are in the building codes (chs. SPS 320 to 325 and 361 to 366).
Mixing and temperature-limiting valves (SPS 382.40 (8) (g))
| Application | Standard |
|---|---|
| All showers in public buildings | ASSE 1016/ASME A112.1016/CSA B125.16 thermostatic, pressure-balanced or combination valve; a thermostatic or combination valve may not be bypassed |
| Master mixing valve at or near the heater | ASSE/ANSI 1017; not for point-of-use or emergency equipment |
| Sinks, bidets, lavatories, tubs without shower heads | ASSE 1070 |
| Fixtures where the bather can't reach the adjustment and no downstream mixing occurs | ASSE 1069 |
| Emergency eyewash, eye/face wash, drench showers | ASSE 1071 |
Health care facilities have additional maximum outlet temperatures; see section 11.1.
Exam traps
- A T&P valve's steam rating, not just its pressure, must be at least the heater input. A 199,000 BTU/h heater needs a valve rated at least 199,000 BTU/h.
- A 1017 valve at the heater does not satisfy a public shower's 1016 requirement.
- The 100-foot circulation trigger is measured as developed length from the source to the fixture.
A water heater has an input of 75,000 BTU per hour. What must be true of its combination temperature and pressure relief valve?
Its temperature steam rating must be at least 75,000 BTU per hour
Its pressure setting must equal the main pressure
It must have a shutoff valve for service
Its sensor must be within 6 inches of the tank bottom
Which T&P relief valve discharge pipe installation complies with SPS 382.40 (5) (d) 5.?
A 3/4-inch pipe with a threaded end, 4 inches above a floor drain
A 3/4-inch pipe ending 4 inches above the floor in the heater room, with an unthreaded end
A 1/2-inch pipe reduced from a 3/4-inch valve outlet
A 3/4-inch pipe run through a trap to the floor drain
Under SPS 382.40 (8) (g), what standard applies to mixing valves controlling water temperature to showers in public buildings?
ASSE 1070/ASME A112.1070/CSA B125.70
ASSE 1071 tempered water for emergency fixtures
ASSE 1016/ASME A112.1016/CSA B125.16
ASSE 1017 master mixing valve at the heater
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