CSLB C-36 Plumbing ContractorFixture and Appliance InstallationEasy
A plumber is installing a new residential water heater. The local code requires a thermal expansion tank. What is the primary purpose of installing a thermal expansion tank in a closed-loop hot water system?
- ATo filter sediment from the incoming cold water supply.
- BTo absorb the increased volume of water caused by heating.
- CTo increase the water pressure in the hot water lines.
- DTo prevent backflow of hot water into the cold water supply.
Show answer & explanationAnswer & explanation
Correct answer: B. To absorb the increased volume of water caused by heating.
When water is heated, it expands. In a closed-loop system, this expansion can create excessive pressure. A thermal expansion tank provides a space for this expanded water, protecting the plumbing system and water heater from damage.
Why the other options are wrong
- A. Sediment filters are separate devices and not the function of an expansion tank.
- C. Expansion tanks absorb pressure, they don't increase it; they prevent excessive pressure buildup.
- D. Backflow prevention is handled by check valves or backflow preventers, not expansion tanks.
Thermal Expansion Tank Purpose
A thermal expansion tank is installed in a closed-loop hot water system to absorb the increased volume of water that results from heating, preventing excessive pressure buildup and protecting the plumbing system.
- Protects against thermal expansion.
- Prevents excessive pressure.
- Extends life of water heater and plumbing.
Memory trick: Hot water expands, the tank expands with it, keeping pipes intact.