IRC 2024 Shower Valves: Anti-Scald (Pressure Balancing) Valve Required

What IRC 2024 § P2708.3 requires

Yes. IRC 2024 Section P2708.3 requires that all showers and tub-shower combinations be equipped with individual pressure-balancing or thermostatic mixing valves with a high-limit stop. The maximum hot water delivery temperature is 120°F (49°C).

Under IRC 2024, the valves must be listed to ASSE 1016 or ASSE 1070. This requirement applies to all new shower installations and any shower valve replacement done under permit. It protects against scalding when cold water supply pressure drops, such as when a toilet is flushed or a washing machine fills.

IRC 2024 P2708.3 states that shower and tub-shower combination valves shall be of the pressure-balancing, thermostatic mixing, or combination pressure-balancing/thermostatic mixing type that complies with ASSE 1016. The valve must have a maximum hot water setting of 120°F (49°C). The code does not specify a minimum water temperature — only the maximum delivery temperature limit — because the objective is to prevent scalding, not to establish a comfortable shower temperature.

A pressure-balancing valve maintains a constant ratio of hot to cold water pressure even when one supply pressure changes. When a toilet is flushed, the cold water supply pressure momentarily drops as the fill valve opens. Without a pressure-balancing valve, that drop shifts the ratio of hot to cold water flowing through the shower valve toward hotter water, and the shower temperature spikes. A pressure-balancing valve detects the imbalance and restricts both the hot and cold sides proportionally, keeping the water temperature approximately constant until equilibrium is restored.

A thermostatic mixing valve is a more sophisticated device that maintains a set output temperature regardless of supply pressure or temperature fluctuations. It uses a thermostatic element (a wax or bimetallic actuator) to continuously adjust the mixing ratio. Thermostatic valves are more expensive than pressure-balancing valves but provide superior temperature control, are preferred for accessible showers and institutional settings, and can be used in multi-function shower systems where multiple outlets are controlled from a single valve body.

Both pressure-balancing and thermostatic valves must have a high-limit stop — an adjustable mechanical stop that prevents the valve handle from being turned to a position that delivers water above the 120°F maximum. The high-limit stop is typically set by the plumber or contractor during installation to the appropriate maximum temperature for the household. For households with young children, elderly occupants, or persons with reduced sensitivity to heat (such as diabetics), the high-limit stop is often set to a lower temperature such as 110°F or 115°F.

ASSE 1016 is the American Society of Sanitary Engineering standard for performance, materials, and testing of individual pressure-balancing and thermostatic shower valves. Compliance with ASSE 1016 is required by the code; valves must be listed by a recognized testing laboratory to this standard. The listing mark (typically CSA, IAPMO, or NSF) and the ASSE 1016 reference should appear on the valve body or packaging.

ASSE 1070 is the standard for water temperature limiting devices, which are separate thermostatic mixing valves installed at the point of use rather than at the water heater. P2708.3 allows ASSE 1070-listed devices as an alternative or supplementary approach to temperature control at shower outlets.

Why This Rule Exists

Scald burns from hot water are a leading cause of residential burn injury in the United States, and shower scalds are among the most severe because the body exposure surface area is large and the exposure duration can be significant before the person can react and escape. Children and elderly adults are at the highest risk: children have thinner skin that burns at lower temperatures than adult skin, and elderly adults have slower reaction times and may have reduced temperature sensation due to neuropathy or medications.

At 120°F, a full-thickness burn can occur in about 5 minutes of exposure. At 130°F, that time drops to 30 seconds. At 140°F (a common water heater setting), full-thickness burns occur in 5 seconds. A shower temperature spike from 105°F to 130°F — caused by a flushed toilet drawing cold water pressure — is enough to cause a serious burn before the person can exit the shower enclosure, particularly if that person is a child or elderly adult.

The pressure-balancing valve requirement was first added to the IRC in 1992 after evidence from hospital burn units confirmed the causal relationship between pressure spikes in shared supply systems and scalding burns. The requirement has been refined over subsequent code cycles and now extends to all shower and tub-shower combinations in new residential construction.

What the Inspector Checks at Rough and Final

At rough-in, the inspector checks that the shower valve location and supply connections are correctly stubbed out and that the valve body is listed for the application. Some inspectors ask for the valve brand and model at rough-in to verify ASSE 1016 compliance, particularly in jurisdictions where knockoff or unlisted valves have been a persistent problem.

At final inspection, the inspector verifies that a pressure-balancing or thermostatic mixing valve is installed at the shower or tub-shower, that it is listed to ASSE 1016, and that the high-limit stop is accessible and set. The inspector may check the water temperature at the showerhead using a thermometer or simply confirm the high-limit stop is engaged at a position consistent with a maximum 120°F delivery. Some inspectors run the hot water to verify that the showerhead output does not exceed 120°F.

The inspector also checks that the valve trim (handle, escutcheon plate, and volume control) is installed and that the valve handle operates through its full range without binding. A pressure-balancing cartridge that is seized or incorrectly installed will fail to balance pressure, defeating the code purpose even in a listed valve body.

What Contractors Need to Know

Use only ASSE 1016-listed pressure-balancing or thermostatic valves. Do not install a two-handle (separate hot and cold) shower valve in new construction — this configuration is not compliant with P2708.3 because it has no pressure-balancing mechanism. The code requires a single mixing valve that maintains temperature balance automatically.

Set the high-limit stop at installation before installing the handle trim. Most pressure-balancing valves come with the high-limit stop set at a factory default position, but that position may allow water temperatures above 120°F depending on the water heater setting. Test the hot water temperature at the showerhead with a thermometer and adjust the high-limit stop accordingly. Document the adjustment in the project record.

For tub-shower combinations, a single ASSE 1016-listed valve with a diverter to the showerhead meets the code requirement. The same valve that fills the tub also serves the shower. Both positions (tub fill and shower) are covered by the anti-scald protection of the pressure-balancing cartridge.

Coordinate the shower valve rough-in height with the shower system being installed. A standard pressure-balancing shower valve rough-in height is typically 48 inches above the finished floor to the valve centerline, though this varies by fixture package and designer preference. Confirm the valve rough-in height with the tile setter and fixture installer before closing the wall.

For digital or multi-function shower systems with volume controls, body sprays, and multiple outlets, verify that the master thermostatic valve is ASSE 1016 compliant and that all outlets are served by the anti-scald protection of the master valve. Individual volume controls for body sprays do not need to be ASSE 1016 listed if the master thermostatic valve is.

What Homeowners Get Wrong

The most common homeowner mistake is replacing a failed pressure-balancing cartridge with a non-pressure-balancing cartridge because it was the only part available at the hardware store. Not all cartridges for a given valve brand are pressure-balancing, and installing a standard (non-pressure-balancing) cartridge in a valve body that was originally listed as ASSE 1016 defeats the anti-scald protection. Always verify the replacement cartridge is the correct pressure-balancing type for the valve model.

Another mistake is setting the water heater too high and relying on the shower valve to limit temperature. Some homeowners set their water heater to 140°F or 160°F for legionella prevention or because they believe hotter is cleaner. A pressure-balancing valve limits the ratio of hot to cold but does not thermally limit the hot supply. If the hot supply is 160°F and the cold supply drops suddenly, the valve may still briefly deliver very hot water before pressure equalization occurs. For households with high water heater settings, a separate thermostatic mixing valve (ASSE 1017-listed) at the water heater is the more reliable approach to limiting delivery temperature throughout the house.

Many homeowners also do not realize that two-handle shower faucets are no longer compliant for new installation. Homeowners who want to replace a two-handle shower with a matching two-handle set during a permitted renovation will be required to install a compliant pressure-balancing valve instead. The two-handle configuration, while still available for sale, is not compliant with P2708.3 for new work.

State and Local Amendments

California’s plumbing code adopts the anti-scald valve requirement with additional provisions regarding the high-limit stop temperature setting. Some California jurisdictions require the high-limit stop to be set to 110°F rather than 120°F in residential projects. Florida, New York, and Massachusetts have similar anti-scald requirements in their residential plumbing codes.

Some jurisdictions also require anti-scald protection at lavatories and kitchen sinks in residential care facilities, assisted living facilities, and housing for elderly or disabled persons, going beyond the IRC’s specific P2708.3 requirement, which applies only to shower and tub-shower installations. For any residential project serving special populations, verify the applicable standard with the local authority having jurisdiction.

When to Hire a Professional

Hire a licensed plumber for all shower valve rough-in work, for valve replacement during permitted renovations, and whenever the high-limit stop adjustment requires access to the valve internals behind the wall. Thermostatic mixing valves are more complex than pressure-balancing valves and require professional installation to set correctly, particularly for multi-outlet digital shower systems.

If the existing shower valve is a two-handle type and the renovation is permitted, a plumber will need to replace the valve body (not just the handles or cartridges) with a compliant single-body pressure-balancing or thermostatic valve. This typically requires opening the shower wall, which should be coordinated with the tile contractor and waterproofing installer.

Common Violations Found at Inspection

• Two-handle (separate hot and cold) shower valve installed in new construction or permitted renovation, which lacks pressure-balancing function and is not ASSE 1016 compliant.
• Pressure-balancing valve installed without a high-limit stop, or with the high-limit stop set to a position that allows water above 120°F.
• Valve not listed to ASSE 1016; non-listed import or off-brand valve installed in place of a listed product.
• Pressure-balancing cartridge replaced with a non-pressure-balancing cartridge during a repair, defeating the original listed valve’s anti-scald protection.
• Tub-shower combination with a tub fill valve that does not have pressure-balancing protection on the showerhead diverter path.
• High-limit stop set at factory default without field verification that the actual delivery temperature does not exceed 120°F.
• Thermostatic mixing valve installed but thermostatic element not functioning correctly due to incorrect orientation or a damaged element.
• Shower valve handle travel does not cover the full range of the pressure-balancing cartridge due to an incorrect trim kit or misaligned cartridge.
• Multi-function shower system with body sprays or additional outlets not served by the ASSE 1016-listed thermostatic valve anti-scald protection.
• Volume control valve installed upstream of the pressure-balancing valve, reducing cold supply pressure before it reaches the balancing mechanism.