2.3 Flushing Devices, Water Conservation & Temperature-Limiting Controls

Why this section matters

Flushing devices and temperature controls sit where fixtures, water supply and backflow meet, so exam writers like them. Learn the numbers in Tables 604.3 and 604.4 and the standards in 412 and 415.

Flushing devices (415)

• 415.1: Every water closet, urinal, clinical sink, and any fixture that relies on trap siphonage to empty must have a flushometer valve, flushometer tank or flush tank. That device must deliver enough water to flush, clean the fixture and refill the trap. Under 415.1.1, one flushing device may serve only one fixture.
• 415.2, flushometer valves and tanks: These must conform to ASSE 1037/ASME A112.1037/CSA B125.37 or CSA B125.3. Their vacuum breakers must meet ASSE 1001 or CSA B64.1.1 and must be accessible. A flushometer valve must be the water-conservation type and must not be used where pressure is below its operating minimum. It must close positively, have a way to regulate flow, and refill the trap seal automatically.
• 415.3, flush tanks: A device must refill the tank and shut off fully. The antisiphon fill valve must conform to ASSE 1002 and be set at least 1 inch above the full opening of the overflow pipe (415.3.1).
• 415.3.2: The tank overflow discharges into the fixture and is sized for the maximum fill rate.
• 415.4: Flush pipes and fittings must be nonferrous.

How the main types work

• Gravity flush tank: stored water drops into the bowl when the flapper opens. It works on low pressure but refills slowly.
• Flushometer tank (pressure-assisted): supply pressure compresses air in a sealed vessel to give a strong flush from a tank. Table 604.3 calls for 1.6 gpm at 20 psi.
• Flushometer valve: connects directly to the supply and meters a flush in seconds. A diaphragm or piston valve stays closed because pressure on its upper side, fed through a small bypass, outweighs the force below. Tripping the handle vents the upper chamber and opens the valve, and the bypass then refills the chamber to close it.

Supply needs for flush valves

Vacuum breakers on flush valves

A flushometer valve feeds water straight into a bowl of waste, so back-siphonage protection is critical. The atmospheric vacuum breaker must be set with its critical level (CL) at least 6 inches above the flood level rim of the fixture (608.16.4). If no CL mark is shown, use the bottom of the vacuum breaker as the critical level. Vacuum breakers may not be installed under exhaust hoods or other places that hold toxic fumes.

Water consumption limits (Table 604.4)

The exceptions in 604.4 are blowout water closets using no more than 3-1/2 gallons per flush, vegetable sprays, clinical sinks using no more than 4-1/2 gallons per flush, service sinks and emergency showers. EPA WaterSense labels (1.28 gallons per flush for water closets, 0.5 gallon per flush for urinals, 1.5 gpm for lavatory faucets) are voluntary efficiency labels, not IPC maximums.

Temperature-limiting controls

Hot water heaters are often set near 140°F to limit Legionella growth. Water that hot can cause a full-thickness burn in adult skin in about 5 seconds, while at 120°F it takes several minutes. The IPC therefore limits the delivered temperature at the fixture rather than the storage temperature.

• An in-line thermostatic valve may not be used to meet 412.3.
• An ASSE 1062 temperature-actuated flow-reduction device may limit a faucet to 120°F, but it may not replace the required shower or tub valve (412.7).
• Pressure-balance valves keep the hot-to-cold ratio steady when the pressure on one side drops. Thermostatic valves sense the mixed-water temperature.

Commercial items linked to fixtures

• Food waste disposers (416):
  • Domestic units conform to ASSE 1008 and UL 430. Commercial units are listed to UL 430.
  • Domestic and commercial units drain through at least 1-1/2 inches, and a commercial unit is trapped separately.
  • Every disposer needs a cold water supply protected by an air gap or a backflow preventer.
  • A disposer may not discharge to a grease interceptor (1003.3.2).
• Commercial dishwashing machines discharge through an air gap or air break into a waste receptor (802.1.6). Domestic dishwashers connect to a wye on the sink tailpiece, to the disposer's dishwasher inlet, or through an air break to a standpipe. Their discharge line must rise and be fastened to the underside of the counter (409.4).
• Service sinks and hose bibbs: any opening with hose threads must have a vacuum breaker or a permanently attached hose-connection vacuum breaker (608.16.4.2).

Exam traps

• Flush valve pressure: 35 psi (siphonic) or 45 psi (blowout), not 15 psi.
• The 1.28 gallons-per-flush figure is a WaterSense label, not the code maximum of 1.6.
• Public lavatory faucet: 0.5 gpm, or 0.25 gallon per metering cycle.
• Shower limit 120°F; public lavatory tempered water 110°F.