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Water Heaters and the Poet Virgil

Aegrescit medendo, a latin phrase attributed to the poet Virgil meaning, “the disease worsens with the treatment” may also be translated into the more common english phrase, “the cure is worse than the disease.” I’m not certain of the context, but the poet may have been speaking about certain do-it-yourself home repairs.

When constructing a home inspection report, I try to strike a balance between providing enough but not too much information about any given issue. With many issues, I adopt the mantra, “less is more”. With others, especially with those where an improper homeowner repair may make things worse, I opt to provide what I hope will be enough information to help ensure that the job gets done right. One such issue is the lack of a discharge pipe to serve the temperature, pressure-relief (TPR) valve on a water heater.

The TPR valve is an important safety feature that keeps the water heater from exploding if the temperature and pressure in the water heater build beyond what it can safely contain. The TPR valve is the last line of defense in case other safety features of modern water heaters fail to prevent explosive conditions. In such an event, instead of an explosion, scalding water under pressure will discharge through the TPR valve. The TPR valve needs a discharge pipe to divert pressurized scalding water to the floor or to another approved location.

During a professional home inspection, a Pennsylvania home inspector or a Delaware home inspector will check for the presence or absence of the discharge pipe. If missing or in need of improvement, it will be noted in the home inspection report. But how much information is enough information in this instance?

A “less is more” approach may result in a comment such as, “The water heater TPR valve needs a discharge pipe for safety.” The problem with such an approach is that attaching a pipe improperly could result in a condition that is at least as dangerous – and potentially much more dangerous – than having no pipe at all. Aegrescit medendo.exploding_water_heater

An improperly connected pipe could result in personal injury, property damage, contamination of the potable water supply or, at worst, an explosion. If you’re thinking, “What’s the big deal?”, Google “exploding water heater” and see what you find.

With that in mind, I like to provide my clients with all the information that I think is needed to help ensure that, especially if they attempt the repair themselves, the job gets done right.

What follows are the detailed requirements for the installation of the discharge piping as found in the 2015 edition of the International Residential Code©.

P2804.6.1 Requirements for discharge pipe. The discharge piping serving a pressure-relief valve, temperature-relief valve or combination valve shall:

  1. Not be directly connected to the drainage system.
  2. Discharge through an air gap located in the same room as the water heater.
  3. Not be smaller than the diameter of the outlet of the valve served and shall discharge full size to the air gap.
  4. Serve a single relief device and shall not connect to piping serving any other relief device or equipment.
  5. Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor or to the outdoors.
  6. Discharge in a manner that does not cause personal injury or structural damage.
  7. Discharge to a termination point that is readily observable by the building occupants.
  8. Not be trapped.
  9. Be installed to flow by gravity.
  10. Terminate not more than 6 inches and not less than two times the discharge pipe diameter above the floor or waste receptor flood rim level.
  11. Not have a threaded connection at the end of the piping.
  12. Not have valves or tee fittings.
  13. Be constructed of those materials listed in Section P2906.5 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.
  14. Be one nominal size larger than the size of the relief-valve outlet, where the relief-valve discharge piping is constructed of PEX or PE-RT tubing. The outlet end of such tubing shall be fastened in place.

Admittedly, that’s a lot to consider for what may have seemed a simple task. If it’s too much to deal with, I have three simple words of advice, “Call a plumber.”

I hope this is helpful.

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