What is a TPR Discharge Pipe and Why it’s Important

Tpr Discharge Lg

Temperature and pressure relief, aka TPR valves, are essential safety features in water heaters. When installing a water heater, you must install the TPR discharge pipe per manufacturer guidelines.

A TPR (Temperature and pressure-relief) is installed on water heaters, such as tank water heaters and boilers. TPRs are made to automatically release water if the temperature or pressure inside the tank exceeds safe levels. When the TPR valve opens, scalding water is released from the tank. A correctly installed TPR discharge pipe directs this scalding water to discharge to a safe location to the exterior or drain location.

Water heater manufacturers state that a TPR discharge pipe is required to direct hot water to the exterior or a suitable drain location. TPR discharge pipes are required to be made of copper, CPVC, or PEX pipe. PVC piping or plastic tubing is unsuitable for a discharge pipe due to the scalding water temperatures.

TPRs are temperature and pressure sensors and safety devices. In case they malfunction, the water in the tank could get superheated. The TPV valve releases pressure inside the tank to prevent water heaters from exploding. TPR valves without a discharge pipe could release scalding hot water causing bodily injury.

If you want to prevent such a situation from ever happening, there is a need to install a TPR discharge pipe and must consider the best option. This article will concentrate on the TPR discharge and focus more on the three different options: copper, CPVC, and PEX.

Requirements of Discharge Pipes

All discharge pipes must meet some basic requirements. A discharge pipe must: 

  • Be designed and developed from approved materials, including copper, polyethylene, CPVC, stainless steel, polypropylene, and galvanized steel. Non-approved plastics and PVC should never be used since they are prone to melting.
  • Never be smaller compared to the actual diameter of the pipe outlet valve it is supposed to serve.
  • Never decrease in size from the valve to the point of discharge (air gap).
  • Be as straight and short as possible to prevent undue stress of valves.
  • Be installed to drain by gravity.
  • Never be trapped because standing water can be contaminated and flow back into potable water. 
  • Discharge to the outdoors, an indirect waste receptor or floor drain. 
  • Not be linked to the drainage system.
  • Discharge through visible air gaps available in the same room as water-heating appliances.
  • Be piped to an indirect waste receptor first through the air gap.
  • Never terminate above 152 mm (6 inches) above the waste receptor or floor.
  • Discharge in a way that doesn’t lead to scalding.
  • Discharge in a way that doesn’t lead to property or structural damage.
  • Discharge to the ending point that’s observable by occupants. 
  • Be piped differently from other water heater pans, relief valve discharge, or equipment drains piping to the end of discharge. 
  • Never contain valves anywhere.
  • Never possess tee fittings.
  • Never possess a threaded connection at the termination of the pipe to prevent capping.

Activation and Leakage

A fully functioning TPR valve ejects powerful jets of hot water out of the discharge pipe when it’s fully activated. Therefore, a leak from the TPR valve indicates the need for a replacement. If the TPR activates, you should shut off the valve immediately and contact a professional plumber for repair and assistance. 

Inspectors make recommendations for the testing of TPR valves at least every month. However, inspectors should do this themselves. The best thing they can do is explain to the homeowners where the main water supply can be located and how it can be disconnected. 

TPR Data Plate Information

Here are some things you should know about the data plate:

  • Any TPR that doesn’t have a data plate should be immediately replaced.
  • The BTU/HR rating on the data plate water-heating appliance should never be more than that of the TPR. The ratings of the TPR are on its data plate.
  • The pressure that will activate the TPR is printed on the data plate that’s found below the test lever. The mount should never go above the working pressure limit that is available on the data plate 
  • of the appliance that it serves. 

Even though the chances of a TPR valve being activated are closer to zero, it’s still a critical safety component on domestic water heaters and boilers. Guidelines involving the discharge pipes and valves reflect real hazards that all home inspectors and homeowners must consider seriously. 

Fixing Leakages in Temperature Pressure Relief Valves

When you find your TPR valve malfunctioning, you might have to make a quick replacement. Managing a replacement is simple, and in most cases, you can even do it yourself. Follow the steps below to achieve this:

  1. Start by turning off your water heater breaker.
  2. Proceed to shut off the water.
  3. Drain the bottom to empty water from the water heater.
  4. Using a wrench, remove the discharge tube and TPR valve. 
  5. Replace with a new discharge tube and TPR valve.
  6. When you are done, turn the water back slowly. You can also turn on the water heater. 

Comparing Labor Costs of Different Types of TPR Discharge Pipes

For the past 30 years, copper has been the dominant discharge pipe used in at least 80% of home constructions. However, CPVC has seen steady growth in the last few years.

CPVC is popular with do-it-yourselfers and remodelers since it doesn’t involve soldering pipes and sweating. 

Each type of TPR discharge pipe comes with its advantages, disadvantages, and purpose. But, in most cases, the main difference between PEX and CPVC comes down to how familiar you’re with materials and the plumbing functionality and materials that you’re after.

You employ either copper, PEX, or CPVC tubing without experiencing significant problems. However, you should ensure that they’re installed by someone familiar with their best practices. To enable you to come up with an enlightened decision on which option is the best fit for you, we’ll explore each material and illustrate the ups and downs.

CPVC for Plumbing

Like we have seen above, CPVC piping is the best option for do-it-yourselfer and remodelers. The option has been around for over 40 years now. It’s rated for temperatures of at least 140 degrees. 

This piping option is very safe to use, just like copper piping. The good thing about CPVC is that it can handle high amounts of heat and has a high resiliency. 

CPVC has a different and unique outer diameter compared to PEx and copper. It is something that you should consider while planning your connections. CPVC is also easy to install and highly lightweight compared to copper. 

This piping option has a lower cost compared to copper. It can be attributed to the cost of metals increasing over the past few years. 

Pros of Using CPVC

  • High impact strength
  • Resistance to abrasion and corrosion
  • Cost-effective and easy installation
  • Has a smooth bore for better flow (also decreases water noise)
  • It’s competitively priced against copper, thus less subject to job site theft
  • Lightweight
  • It’s self insulated to reduce thermal loss
  • Virtually no condensation of sweating
  • Stops pressure leaks at the solder joints
  • Non-conductive
  • Has a low smoke density and is flame retardant
  • Eliminates water hammer due to flexibility
  • Dormant to corrosive water supplies and acidic soils
  • Possible to bury it directly under slabs without chemical interaction

Considerations When using CPVC

You should note that CPVC:

  • They are subject to cracking when there are earthquakes
  • Requires at least a 24-hours cure period during cold weather before being pressurized with water

All national building codes approve the use of CPVC in Canada and the United States to carry potable water. In addition, quality control standards and extensive testing have been established to ensure that these products are manufactured with consistency. 

Copper Piping Option

For a long time, copper piping has been referred to as the workhorse product of the United States. The use of copper has been around since the 1920s. 

By the 1980s, copper for water piping purposes was more than half a billion linear feet each year. As a result, copper piping offers one of the best solutions for commercial and home piping, provided that you keep the supplied water near a pH of 7. 

However, many people have raised the challenge of pinhole leaks. Pinhole leaks that result from corrosion inside the pipes occur in most older homes in cases where the supply lines are horizontal. The pipe walls are therefore disrupted in a non-uniform fashion.

The leading causes of pinhole leaks include high pH, excessive flow rates, and water softeners. 

Pros of Copper Option

  • Tolerant to earthquakes.
  • Biostatic since it doesn’t support bacterial growth.
  • Has proven durability of 15 to 20 years in non-acidic installations.
  • Has light joints.
  • Widely allowed by all building codes.
  • Has a melting point of 1981°F, thus being resistant to fire.
  • The melting point is five times that of CPVC.
  • Has a smaller external diameter compared to CPVC.
  • Fast cure time.
  • Highly rated for internal working pressure.
  • Available ion is drawn (hard) and annealed (soft) versions.
  • It can be bent to prevent obstructions, minimizing joints.
  • It is 99.9% copper/silver as per the ASTM specification

Cons of Copper Option

  • Repairs are complex for those who want to do it by themselves, thus requiring special tools and training.
  • Some people report that water has a metallic taste.
  • Its pricing is very volatile, meaning that it can experience a steep increase based on market forces.
  • In the presence of acidic water, there can be water leaks. 
  • There could be a fire hazard if you were to install it with a gas torch.
  • There are areas where copper piping can only be applied when the pH is less than 6.5 (acidic).
  • Can leach copper or lead into the water supply.
  • A skilled plumber is required since the installation process is intensive.
  • Can compress water flow due to calcium build-up.
  • The higher installation cost for both materials and labor.
  • Require insulating jackets due to thermal loss.
  • Noisy with high water velocities.
  • If there is no proper insulation, condensation is possible.
  • You might be required to have water hammer arrestors to prevent damage in case of water hammer at high velocities.
  • When the temperatures are high, copper joints can fail.

Although there are no listed side effects of copper piping, the EPA lists copper among metals that contaminate drinking water. In addition, older copper installations might have higher levels of lead which is poisonous. 

PEX Tubing

PEX tubing also means cross-linked polyethylene. It’s the fancy approach of illustrating the process through which the plastic pipe is made. What cross-linking does is create a link between the polymer chains. 

Manufacturers employ three methods to manufacture PEX piping: PEX A, B, and C. There is an extrusion process that heats the material under high pressure. The tubing is eventually pulled out through a die. 

PEX tubing has been used since the 1980s strictly for commercial purposes. However, many installers prefer using PEX due to its flexibility and can run for long distances in a single run. It, therefore, saves more time during installation compared to CPVC and copper. 

Why Should You Use PEX Tubing

One of the main reasons PEX is preferred among most people is that it can operate in a wide range of temperatures. The range can be from below-freezing temperatures to above 180 degrees Fahrenheit. As a result, it makes PEX the ideal solution for cold and hot potable water hydronic radiant floor heating systems, service lines, and supply lines. 

PEX can penetrate the slab and be installed under the slab with only a sleeve. The piping runs in home-run configuration, which involves cold and hot runs directed from a single source to a destination tap, fixture, and spigot. To modify or repair the fixture, you need to shut down one line. 

Plumber working on PEX piping can save time since they are easier and quicker to install. In addition, installation can be managed using either compression-style or mechanical fittings. 

When you install PEX piping correctly, they’re expansion tolerant and highly durable.


From what we have seen above, CPVC comes out on top as the most reliable TPR discharge pipe. In addition, it stands out for being straightforward and cost-effective. 

PEX piping comes second and becomes less expensive when you eliminate the expenditure on tools. Copper piping is the most expensive option. However, there are some homeowners and pros who consider copper a premium high-end solution. 

In our own opinion, we would go for PEX if we were creating our own homes and building new constructions. However, when it comes to older homes, we convert all copper to CPVC where possible. Therefore, we only use copper to save energy and time converting to CPVC and vice versa. 

However, it would be best to understand that there is no wrong answer in the copper vs. PEX vs. CPVC debate. You need to find the perfect material for yourself and your plumber. We hope that this guide illustrates the variables involved in deciding the perfect approach for you. 


Hubert Miles | Licensed Home Inspector, CMI, CPI

Hubert Miles is a licensed home inspector (RBI# 2556) with more than two decades of experience in inspection and construction. Since 2008, he has been serving South Carolina through his company, Patriot Home Inspections LLC. As a Certified Master Inspector, Hubert is dedicated to providing his expertise in home inspections, repairs, maintenance, and DIY projects.