Water Heater T&P Discharge, Expansion Control, and Strapping
A property manager replaces a 50-gallon gas-fired water heater in a basement. The home has a 1-inch municipal service with a new pressure-reducing valve and a double-check backflow preventer at the meter. The old heater had no expansion tank. The new heater's T&P relief valve is rated 150 psi and 210°F, and the installer pipes the discharge with 3/4-inch copper for 4 feet, then reduces to 1/2-inch copper for the last 6 feet, terminating 4 inches above the concrete floor. The heater sits in a finished basement with a drywall ceiling; there is no drain pan. The installer also omits seismic strapping because the area has never had an earthquake. The local code is the UPC. The homeowner reports a dripping T&P valve after the installation.
1. Evaluate the T&P relief valve discharge piping and termination. Identify all violations.
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The discharge piping must be the full size of the valve outlet and must not be reduced. Reducing from 3/4 inch to 1/2 inch is a violation because it restricts the relief capacity. The discharge must terminate not more than 6 inches above the floor or at an approved waste receptor, and it must not be threaded or trapped. Terminating 4 inches above the floor is within the 6-inch limit, but the reduced pipe size makes the termination noncompliant. The discharge pipe must be of a material rated for the temperature and pressure, and it must drain by gravity. The inspector should require the entire discharge line to be replaced at the valve outlet size, with no reductions, and terminated at a safe location where the discharge cannot cause injury or damage. The T&P valve itself must be rated for the heater's input and not plugged or capped.
2. Why is the T&P valve dripping, and what is the correct fix for the closed system?
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The dripping is likely caused by thermal expansion. The new pressure-reducing valve and double-check backflow preventer create a closed system, so when the water heater heats water, the expanding water has nowhere to go and the pressure rises until the T&P valve opens. A dripping T&P valve is a symptom, not the root cause. The correct fix is to install a listed thermal expansion tank on the cold-water side of the water heater, sized for the system volume and pressure, and to verify that the system pressure is set correctly. The inspector should not accept a higher-rated T&P valve or a plugged valve as a solution. The expansion tank must be supported and connected so that it can be isolated and serviced. After the tank is installed, the T&P valve should be checked for proper reseating and the system pressure re-tested.
3. Are the missing drain pan and seismic strapping violations? Explain the conditions that trigger each requirement.
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The missing drain pan is a violation if the water heater is installed in a location where leakage can cause damage. A finished basement with a drywall ceiling is exactly the kind of location where a pan is required. The pan must be at least 1-1/2 inches deep, be sized to the heater, and drain to an approved location. The missing seismic strapping is also a violation if the jurisdiction enforces seismic restraint requirements. The installer's statement that the area has never had an earthquake is not a code defense; the requirement is based on the adopted code and the seismic design category, not on personal experience. Strapping must be installed in the upper and lower thirds of the tank, and the tank must be anchored so that it does not move during an earthquake. The inspector should require both corrections before approving the installation.