Expansion Tanks

66 products

Friendly National Boiler Supply customer support expert smiling in a clean mechanical room office setting.

Need help finding a replacement part?

Fill out the part request form and someone will get back to you shortly.

PART REQUEST FORM

Protect your hydronic boiler system from dangerous over-pressurization with commercial-grade boiler expansion tanks. Designed to absorb thermal fluid expansion as boiler water heats, our selection of pre-charged diaphragm and bladder expansion tanks ensures consistent system pressure, prevents relief valve weeping, and extends boiler life.

Hydronic Thermal Expansion Tanks for Residential & Commercial Boilers

When water is heated inside a closed-loop hydronic heating system, it expands in volume. Without a functioning boiler expansion tank, this thermal expansion rapidly increases system pressure, triggering the boiler's pressure relief valve and introducing unwanted air into the system.

Expansion Tank Types & Options

  • In-Line Diaphragm Expansion Tanks: Compact pre-pressurized tanks for residential hydronic heating loops and light commercial boilers.
  • ASME Commercial Bladder Tanks: Heavy-duty, code-compliant expansion tanks designed for large commercial heating plants, municipal facilities, and industrial hydronic systems.
  • Potable vs. Heating System Tanks: Heavy-duty butyl/EPDM diaphragms engineered specifically for oxygenated water loops or closed-loop hydronic heating.