Water Heater Drip Pans and Relief Valves

Water Heater Drip Pan Requirements
1. Install a drip pan under storage tank water heaters located where leakage could cause damage. The IRC does not specify these locations. They often include attics and all areas within the conditioned area of the home, including finished basements. This provision does not apply to demand type (tankless) water heaters.
2. Use a drip pan at least (≥) 1 ½ inches deep and made with at least (≥) 24 gage galvanized steel or other approved materials. Use a pan with a size and shape to catch all leaks and condensation from the water heater.

Water Heater Drip Pan Discharge Pipe
1. Use at least (≥) a ¾ inch diameter discharge pipe to drain the drip pan. Use a larger discharge pipe if the connection to the drip pan is more than (>) ¾ inch diameter.
2. Run the discharge pipe to an indirect waste receptor (such as a floor drain) or to outside the building. If the discharge pipe terminates outside the building, locate the outlet at least (≥) 6 inches and not more than (≤) 24 inches above the adjacent ground surface.

Water Heater Relief Valves
1. Install either a separate temperature relief valve and a separate pressure relief valve or a combination temperature and pressure relief valve on all appliances used to heat or store hot water. Combination temperature and pressure relief valves (T & P valves) are used almost exclusively in modern water heaters. This provision applies to tank-type, tankless, and swimming pool water heaters.
2. Install the temperature relief or T & P valve on the top of the water heater or on the side of the water heater within 6 inches of the top. Do not install an extension pipe between the water heater and the T & P valve.
3. Do not install a check valve or shutoff valve anywhere that might interfere with the operation of the relief valve or the fl ow of water or steam from the discharge pipe.

Water Heater Relief Valve Discharge Pipe
1. Use water distribution pipe listed in Table P2905-2 as the relief valve discharge pipe. Copper and CPVC are the most commonly used discharge pipes. It is difficult to maintain uniform slope and fall on flexible tubes such as PEX, although such tubes may be used if supported so that slope is maintained. Note that this provision does not apply to manufactured homes.
2. Install the discharge pipe so hot water and steam will not cause personal injury or property damage if the relief valve discharges.
3. Install the discharge pipe so that any leaking from the pipe outlet is readily observable by the building occupants.
4. Use a discharge pipe that is at least (≥) as large as the relief valve opening. This size is usually ¾ inches diameter.
5. Run the discharge pipe full size to the floor, to an indirect waste receptor (such as a floor drain) inside the building, to the water heater drip pan or outside the building. If the area is subject to freezing, terminate the discharge pipe through an air gap into an indirect waste receptor located inside the building. You may use other discharge points in areas subject to freezing, if approved by the local building official.
6. Slope the discharge pipe so that it drains by gravity from the relief valve to the discharge point.
7. Do not connect the discharge pipe directly to the building’s drain, waste, and vent system. Leave an air gap between the discharge pipe and the floor, ground, or other termination point.
8. Do not install a trap, any type of valve, a tee fitting, or a threaded outlet in the discharge pipe.
9. Terminate the discharge pipe through an air gap not more than (≤) 6 inches above the floor.
10. Do not connect more than one appliance to a discharge pipe.

Water Heater Relief Valve Discussion
Improper installation of the T & P valve and discharge pipe is a common problem, particularly when water heaters are replaced. Try to select a water heater that is similar in size and shape to the one being replaced. This will make it easier to install a discharge pipe that slopes toward the outlet point.
PVC pipe is commonly used for discharge pipes in manufactured homes and is acceptable in these homes. Refer to Appendix E for information about IRC application to manufactured homes.