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Is It Code to Have an Expansion Tank on a Water Heater?

is it code to have an expansion tank on a water heater?

The California Plumbing Code (Section 608.3) and the California Mechanical Code (Section 1005.0) require a thermal expansion tank to be installed on all closed plumbing water heating systems.

A pressure regulator blocks the pressure backflow between the main water supply and the house in the closed plumbing systems. As a result, the standard tank water heaters stress your plumbing fixtures and pipes when hot water expands and increase tank pressure.

The California Plumbing Code (CPC) states that an expansion tank must be installed in plumbing systems having backflow preventers, check valves, or any devices blocking the dissipation of plumbing pressure back into the water main.

However, the CPC doesn’t specifically require expansion tanks for tankless water heaters. These only heat up an exact amount of water needed for the occasion and instantly relieve any present pressure; hence the expansion is negligible.

What if you have an older water heating system?

The answer is that the CPC clearly states that all homes must be updated to the current codes when major repairs, modifications, and replacements occur. Consequently, some homes with older water heating systems may not have an expansion tank, but will do so in the next repairs.

How Do Water Heater Expansion Tanks Work?

The expansion tanks absorb any excess volume that occurs when water is heated and expands.

Additionally, they absorb fluctuations in incoming water pressure, stabilizing its flow into the water heater. Water expands when heated, creating an extra volume that may burst your tank when an expansion tank or a temperature relief valve is missing.

Then, how will you know the size of the expansion tank to install?

The standard rule of thumb is that you use a 2-gallon expansion tank for standard water heaters up to 50 gallons in capacity, provided the static supply is less than 60 pound-force per square inch (PSI).

How Do Water Heater Expansion Tanks Work With Temperature Relief Valves?

Safety is an important consideration when installing water heaters in homes. State and federal laws and codes require water heaters and boilers to have temperature and pressure relief valves (T&P) for human safety. The T&P valve automatically vents when water in the tank reaches a certain PSI or temperature, such as 210º F (99º C) or 150 PSI.

Furthermore, CPC Section 608.5 requires one to install an open discharge pipe serving the temperature relief valve, pressure relief valve, or a combination of both.

The discharge pipe has its requirements, such as:

  • Its material should not be rated less than the water heater system’s operating temperature.
  • It should independently discharge by gravity and through an air gap into a drainage system or outside the house. The discharge pipe should also be 6 inches or more above the ground and pointing downwards.
  • Its installation and use should follow all safety protocols.
  • Its terminal end should be free of threads and not capped.
  • No part of the discharge pipe should be subject to freezing.
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