What kind of valve is required on a tub/shower, and what temperature is it supposed to be set to?

Valve Type: A pressure-balancing, thermostatic, or combination pressure-balancing/thermostatic mixing valve is required. It must be listed to ASSE 1016 (or CSA B125.1) and installed at the point of use. Code Ref: IPC 424.3 / IRC P2708.3 / UPC 409.3.

Temperature Limit: The valve must be field-adjusted to limit the mixed-water outlet temperature to a maximum of 120 °F (49 °C). Code Ref: IPC 424.5 / IRC P2708.5 / UPC 409.4.

Practical Notes

• Pressure-balancing valves react to pressure changes (e.g., toilet flush); thermostatic valves react to temperature changes and hold set-point tighter (±2–3 °F). Thermostatic is preferred for multi-head showers or users with mobility issues.
• The 120 °F limit is a final mixed-water temperature at the showerhead/tub spout, not the water-heater setting. Verify with a thermometer at the outlet after installation and after the heater has recovered.
• Most valves ship with the limit stop set conservatively low (often 100–105 °F). You must rotate the limit-stop screw/ring per the manufacturer’s instructions to achieve ≤120 °F at full-hot handle position.
• If the water heater is set above 140 °F for Legionella control, a master thermostatic mixing valve (ASSE 1017) at the heater is also required to deliver ≤120 °F to the distribution system, but the point-of-use ASSE 1016 valve and its 120 °F limit stop are still mandatory at the tub/shower.

For a tub/shower combination, a pressure-balancing or thermostatic mixing valve is required by plumbing codes (such as the International Plumbing Code – IPC Section 408.3 and the Uniform Plumbing Code – UPC Section 408.3) to prevent scalding and thermal shock.

Required Valve Type:

• Pressure-balancing valve (most common in residential): Maintains constant water temperature by adjusting hot/cold mix in response to pressure fluctuations (e.g., when a toilet flushes).
• Thermostatic mixing valve (preferred for safety, especially in homes with children, elderly, or disabled occupants): Maintains a set temperature regardless of pressure or flow changes, offering superior scald protection.

Temperature Setting: The valve must be set to deliver hot water no higher than 120°F (49°C) at the fixture outlet. This is mandated by:

• IPC 408.3
• UPC 408.3
• ASSE 1016 (performance standard for tub/shower valves)
• U.S. Consumer Product Safety Commission (CPSC) recommendations

Why 120°F? Water at 140°F can cause third-degree burns in under 5 seconds; at 120°F, it takes over 5 minutes — providing a critical safety margin.

Installation Note: The valve must be accessible for service (not buried in the wall without an access panel). If replacing an old valve, ensure the new one is ASSE 1016-certified and compatible with your plumbing system (copper, PEX, etc.).

If unsure about valve type, installation, or local code amendments — consult a licensed plumber. Improper installation can lead to scalding hazards or code violations.

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