- Q.Is it acceptable to use
plastic piping for the pressure-relief discharge on a
domestic water heater? The BOCA code in my
area requires that the discharge piping be rated at or
above the temperature of the system, but it’s
not clear whether that refers to the temperature of the
water in the tank or the temperature setting of the
relief valve.
A.Redwood Kardon
responds: Without protection, a domestic water
heater whose thermostat has failed would see a
continuous rise in temperature and pressure. When
the water pressure exceeded the capacity of the
tank (typically 300 psi), the tank would burst with
enough force to send an average-size car 125 feet
in the air (see "Exploding Water Heater,"
Eight-Penny News , 9/93).
A temperature- and pressure-relief valve is
designed to prevent such catastrophic failures. In
my area, we follow the IAPMO (International
Association of Plumbing and Mechanical Officials)
Uniform Plumbing Code , which allows the
use of galvanized steel, hard-drawn copper,
chlorinated polyvinylchloride (CPVC), polybutylene
(PB), or code-listed straight sections of
relief-valve drain tube.
It’s true that the temperature ratings
for CPVC and PB are well under the settings
(210°F or less) for most relief valves. The
consensus among inspectors I’ve talked to,
however, is that the relief cycle for an
excessively high-temperature or high-pressure
condition is so intermittent and short-term that
CPVC or PB are acceptable materials for this
application.
Redwood Kardon is a building
inspector for the City of Oakland, Calif., and
author of Code Check : A Field Guide
to Building a Safe Home . An online version
of Code Check can be found on the Web
at www.codecheck.com.