An expansion tank is a small tank installed on a water heater or hydronic heating system, containing an air-filled bladder that absorbs the pressure increase occurring when heated water expands within a closed plumbing system, preventing potentially damaging pressure buildup.
This device has become increasingly important in homes with closed plumbing systems, meaning a check valve or pressure-reducing valve prevents heated, expanding water from simply flowing backward into the municipal supply, a common modern configuration that requires this additional pressure management component.
Without an expansion tank in a closed system, the pressure increase from water heating has nowhere to go, potentially causing the water heater’s pressure relief valve to activate frequently or contributing to premature wear on various plumbing components throughout the home.
What Does an Expansion Tank Involve?
- An air-filled bladder absorbing pressure increases
- Installation on the cold water line near the water heater
- Particular importance in closed plumbing systems
- Periodic checking of the internal air charge
Why Are Expansion Tanks Important?
By providing somewhere for the pressure increase from heated, expanding water to go, an expansion tank protects the entire plumbing system from the accelerated wear and potential damage that closed-system pressure buildup could otherwise cause, making this relatively small, inexpensive component genuinely valuable protection. Many local codes now require expansion tank installation specifically in homes with closed plumbing systems.
Because an expansion tank’s internal air charge can gradually diminish over time, periodic checking and, if needed, recharging this component helps ensure it continues providing its intended pressure management function reliably throughout the water heater’s service life.
Expansion Tank vs. Water Heater Expansion Tank
These terms describe the identical device, both referring to the pressure-absorbing tank installed near a water heater in a closed plumbing system, with water heater expansion tank simply being the more specific, complete phrasing.