Quick Answer

The T&P relief valve discharge line must be installed to carry a safety discharge to an approved location without creating a hazard or restriction. Material, sizing, routing, termination, support, freezing exposure, and the water-heater instructions all need to be checked under the adopted plumbing code.

The discharge path is a safety path

A temperature-and-pressure relief valve is designed to protect the water heater under abnormal conditions. The discharge piping must not turn that protective function into a backpressure, scalding, or property-damage hazard.

The 2024 IPC model code addresses discharge piping in Section 504.6. Use that section and the appliance instructions as a starting point—not a generalized internet diagram.

Route and terminate deliberately

A sound field review considers the discharge opening connection, pipe size, material, slope and support, exposure to damage or freezing, and a termination that can discharge safely. Restrictions such as valves or other arrangements that obstruct a safety discharge require careful review under the adopted code.

Do not hide the termination where a discharge cannot be recognized or where it creates a hazard to occupants or property.

Avoid assumptions about materials and drains

A material that is common on one job is not automatically acceptable on another. Match the material, fittings, termination, and drainage connection method to the adopted code and water-heater instructions.

Always verify the code edition adopted by the local jurisdiction, applicable state and local amendments, equipment listing, and manufacturer installation instructions.

Common Mistakes

  • Reducing the discharge pipe size.
  • Adding a shutoff or obstruction in the discharge path.
  • Using unsuitable material or an unapproved route.
  • Terminating where discharge can injure people or damage property.
  • Ignoring freezing and physical-damage exposure.

Bottom Line

T&P discharge piping deserves the same care as the valve itself. Verify the whole path—from valve outlet to safe termination—under the adopted code and equipment instructions.

Sources & References

These official sources support the scope of this guide. Consult the current source and local authority for a project-specific decision.

JL

Author & technical perspective

Jordan Lovell

Building Inspector | Mechanical Plans Examiner | HVAC Contractor

ICC-certified building and trade inspector; ICC Mechanical Plans Examiner; Virginia DHCD Mechanical Plans Examiner; Virginia Master Tradesman — HVAC; Virginia Master Tradesman — Gas Fitting.

Jordan Lovell brings experience from both the contracting and code-enforcement sides of the skilled trades. His background includes residential and commercial building inspection, mechanical plan review, HVAC contracting, field installation, code compliance, and contractor operations. His SkilledCurrent coverage focuses primarily on HVAC, mechanical systems, building codes, inspections, contractor operations, and the intersection between field practice and code compliance.

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