Currently, I only have a T&P relief discharge line that runs down to just above the pedestal and out through the exterior wall. I would like to install a drain pan under the water heater.
I want to cut my relief discharge line and install a tee in order to connect my drain pan's line and allow both to exit using the existing pipe. My concern is that this might allow water flowing down from the relief valve to flow back into the pan and overflow it.
Is this a recommended solution?
Plumbing – Can the water heater’s relief valve discharge line and drain pan line merge into a common pipe
plumbingwater-heater
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Best Answer
The answer is no. This configuration would most likely fail multiple code requirements.
Explanation
You do not mention the diameter of the current discharge pipe, the distance that it runs, how many changes in directions there are, and where it terminates, so I cannot provide a complete answer. However, I can confirm that it would be against code to directly connect the two pipes together due to the resulting cross-connection between a potable system and a drainage system.
The pipe that drains the pan is considered part of a drainage system (either sanitary or storm, depending on what it connects to or where it terminates). The T&P relief valve’s discharge pipe is connected directly to the potable system and as such is considered as part of the potable system. It is against code to directly connect these two systems as the resulting cross-connection allows for the potential of the potable system becoming contaminated.
In addition, there are pipe diameter requirements to be considered.
In a typical installation, the relief valve’s discharge pipe terminates indirectly above the drain pan’s drain opening with an air break that prevents the two systems from being cross-connected. The requirement for a drain pan’s drain pipe is that it be 2 times that of the relief valve’s discharge pipe diameter.
I assume that the diameter of your T&P relief valve’s discharge pipe is the same size as that of the T&P valve’s outlet connection, therefore this pipe cannot be used as the drain pan’s drain pipe, unless you increase the size of it.
Suggestions
Code Requirements (Based on the Canadian Plumbing Code)
Relief Valves
Every hot water heater mush have a pressure relief valve and a temperature relief valve. The two can be combined in one device so long as it meets the requirements for both individual valves:
Relief Valve Discharge Pipe
The requirements of the relief valve discharge pipe are that is must:
In addition, if the relief discharge pipe is longer than 2m (6’ 6”) or if more than two 90° elbows are used, the valve manufacture’s installation instruction must be followed to ensure that the piping does not restrict the valve’s discharge capacity.
Drain Pan Requirements
A drain pan is required when a hot water tank is located in a ceiling or roof space, or over a floor of wood construction. The requirements of the pan are:
Typical Hot Water Tank, Relive Valve, and Drain Pan Configuration:
Note: if the drain pan’s drain connects to a sanitary system, a p-trap (as shown) is required. In addition, the p-trap would require a trap primer.