Plumbing Code: Water heater relief valve

Written by in Design, Water

 In this tutorial you will learn about the codes and regulations concerning the water heater relief valve safety device. If you don’t want to read the code skip to the bottom for a summary.

A typical water heater has a safety device known as a relief valve and is sometimes known as a temperature and pressure valve. If pressure builds or temperatures reach dangerous levels the valve opens up and discharges the pressure. This prevents an explosion. Attached to the relief valve is a discharge pipe. The discharge pipe has both a maximum and minimum distance from the floor according to State plumbing code.

Below is the current plumbing code as written by the Department of Commerce. First I will start with the Department of Commerce official definitions then move forward with the actual pluming code.

Chapter Comm 81  Definitions

Comm 81.01 (126) 

Hot Water: Means water at a temperature of 110 degrees F or more.

Comm 81.01 (281) 

Water Heater: Means any heating device with piping connections to the water supply system that is intended to supply hot water for domestic or commercial purposes other than space heating

Comm 81.01 (188)

 Pressure Relief Valve: Means a pressure actuated valve held closed by a spring or other means and designed to automatically relieve pressure at a designated pressure.

Comm 81.01 (254)

 Temperature & Pressure Relief Valve: Means a combination relief valve designed to function as both a temperature relief and a pressure relief.

Comm 81.01 (255)

 Temperature Relief Valve: Means a temperature actuated valve designed to automatically discharge at a designed temperature.


Plumbing codes for the installation of a temperature and pressure valve

A plumber is required by law to follow the rules according to plumbing code.  Below is what the code book says about the installation of the discharge pipe for a water heater relief valve.

Comm 82.40 (5) (d) (1) and (2) 1-5 (a-f)

Safety devices: Water heaters shall be equipped with safety devices as specified in this paragraph.

1. All pressurized storage-type water heaters and unfired hot water storage tanks shall be equipped with one or more combination temperature and pressure relief valves. The temperature steam rating of a combination temperature and pressure relief valve or valves shall equal or exceed the energy input rating in BTU per hour of the water heater. No shut off valve or other restricting device may be installed between the water heater or storage tank and the combination temperature and pressure relief valve.

2. All pressurized non-storage type water heaters shall be provided with a pressure relief valve installed at the hot water outlet with no shut off valve between the heater and the relief valve.

3. Temperature and pressure relief valves shall be installed so that the sensing element of the valve extends into the heater tank and monitors the temperature in the top 6 inches of the heater or tank.

5. Every relief valve which is designed to discharge water or steam shall be connected to a discharge pipe.

     5 (a) The discharge pipe and fittings shall be made of a material acceptable for water distribution piping in accordance with s.Comm 84.30 (4) (e) 1.

     5 (b) The discharge pipe and fittings shall have a diameter not less than the diameter of the relief valve outlet.

     5 (c) The discharge pipe may not be trapped.

     5 (d) No valve may be installed in the discharge pipe.

     5 (e) The discharge pipe shall be installed to drain by gravity flow to a floor served by a floor drain or to a receptor in accordance with s. Comm 82.33 (8). The outlet of the discharge pipe shall terminate within 6 inches over the floor or receptor, but not less than a distance equal to twice the diameter of the outlet pipe. The discharge pipe may not be threaded.

     5 (f) The discharge pipe for a water heater shall terminate within the same room or enclosure within which the water heater or hot water storage tank is located.


Summary of relief valve code requirements

The plumbing code can be a little confusing if your not a plumber. The above codes were taken directly out of a code book but it’s really simple. The relief valve on your water heater has a pipe attached. Most residential water heaters have a 3/4″ threaded opening for the discharge pipe. By code, you have to run the same size as the opening which means the pipe needs to be 3/4″ in diameter. The pipe itself needs to be either copper, CPVC, or galvanized water piping. Most residential houses have a floor drain that is flush with the finished floor and with the dimensions discussed in the code above the discharge pipe needs to be a minimum of 1.5″ off the floor and a maximum of 6″ off the floor. The pipe can’t have anything attached to it other than a support. The reason why is to prevent a closure in the relief device which would be dangerous. The discharge pipe needs to be in the same room as the water heater.


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