Pressure relief valve

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    • #275239
      Avatar photoMasterPlumbers

        I am selling a house and the inspector has called for the pressure relief valve on the hot water tank to be plumbed outside. Can I plumb it to the crawl space or do I have to plumb it to a drain or can I plumb it up about two feet and over about 8 feet to the outside of the side wall of the house? Thnak you – D

      • #291516
        Avatar photofourth year

          It depends on what your code requires. Our code requires that it pitch downhill and then terminate approximately 9″ above the ground outside the building, or above an approve drain. If yours is the same then you cannot jump up two feet, and neither can you drop into the crawl space and then jump up outside. A approved drain can be subject to an inspector’s decision, but is usually a funnel drain or floor sink.

        • #291517
          Avatar photoGuest

            Your code official is asking that you provide an extra measure of safety and damage-prevention by piping the relief outside. Some precautions are necessary when doing so. Running the pipe above the valve creates the possibility of trapping water above the valve which will act as a possible dirt collector and act as added resistance to flow from the valve.

            Running long lengths of pipe also acts as resistance to flow. It is possible to place a drain below a pipe that terminates some inches above the drain entrance and have drain large enough to allow all the water to leave through gravity.

            What is often forgotten is that in winter a snow line can be some feet above the ground and cover the outlet of an exhaust relief pipe or a drain, so freezing can occur to completely clog the pipe, rendering it useless.

            The inspector was mute about what and how to do this requirement; so some possibilities are to draw alternative piping plans to cover the probabilities and have the inspector approve them one-by-one until he becomes clear in his requirements. There is a possibility that he will make a suggestion in writing to clarify his intent and document his approval.

            “Due to the scalding potential of the discharge from the T&P valve, the outlet from the valve should be piped to a safe area. Typically they are piped down to within 6 inches of the floor or even outside of the dwelling at near ground level. Check with your local building department for local building code requirements.”


            “You should direct the discharge from relief valves to a location in which scalding hot water will not strike people. Also,
            provision must be made to accommodate full discharge of the tank without risk of property damage due to hot water.”

            “According to the Uniform Plumbing Code, a pipe should be connected to the pressure relief valve, extending down along the side of the tank to w/in 6 inches of the floor. This extension pipe prevents the spraying of hot water when the valve is released or if a malfunction occurs.


            “If your water heater is hooked up properly, there is a pipe hooked to this pop-off valve which will direct the venting to an area where it will cause no harm. If your heater is in the house, this will be outside the house by the ground.

            There are two ways to check for the leak. One is to feel this pipe; if it is hotter than just warm, there is a good chance it is leaking. Or you can find where the pipe opens to the outside and look for signs of a leak. The pipe usually ;empties out just above the foundation on the nearest outside wall.

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