TPR Discharge Pipe
The temperature-and-pressure-relief discharge piping that safely directs water away if a water heater relief valve opens.
Applies to
Water heaters · Plumbing
Project example
A replacement water heater needs a correctly sized, routed, and terminated TPR discharge pipe rather than a capped valve.
Also called
Where this term shows up in permit work and how it affects the project
A missing or improper discharge path is a safety and inspection issue that can turn a quick replacement into a correction visit.
If this term appears in a form, plan comment, or local ordinance, start with the building permit guide, compare it against the zoning permit guide, then use the permit guide directory to find the right local path.
Why tpr discharge pipe matters in a permit file
A temperature-and-pressure-relief discharge pipe provides a safe, unobstructed route for hot water and steam if a water-heater relief valve opens. Its size, material, slope, termination, fittings, and visibility are life-safety details—not optional drain-plumbing preferences.
Where it appears in the permit process
Equipment replacement review
The water heater, relief valve, location, drain path, fuel, venting, pan, expansion control, and existing piping are assessed together.
Discharge-path design
The installer selects approved material and routing that maintains required diameter, gravity flow, visibility, and safe termination.
Plumbing installation
The pipe is connected without prohibited valves, caps, restrictions, traps, or unsafe threaded termination and is supported and protected.
Final inspection
The inspector verifies the listed valve, pipe, route, termination, pan or drain provisions, and the complete water-heater installation.
What you may need
- Water-heater and relief-valve model information
- Discharge-pipe material, diameter, route, slope, and termination
- Drain-pan, floor-drain, exterior, freeze-protection, and damage-prevention details
- Expansion-control, shutoff, venting, gas, and electrical information triggered by the replacement
Where to get it or verify it
- Use the adopted plumbing or fuel-gas code and the water-heater manufacturer's instructions.
- Ask the plumbing inspector how local conditions affect approved termination locations.
- Use a licensed plumber where required and for installations with difficult routing or drainage.
Common mistakes that create comments or delays
- Capping, valving, reducing, trapping, or threading the discharge outlet
- Terminating where hot discharge can injure people or damage the building
- Routing uphill or through a condition that can freeze or block flow
- Replacing the heater while leaving an unsafe existing discharge path
What to do next
- Inspect the existing relief valve, discharge route, pan, and drainage before quoting replacement.
- Design a full-size gravity path to an approved visible termination.
- Coordinate material and routing with the listed equipment and local code.
- Keep the complete installation accessible and test-ready for final inspection.