Buffer tanks and vessels FAQ

Buffer tanks and vessels are used in heating and cooling systems to store thermal energy, increase system water volume and help improve system stability and allow equipment to operate more efficiently. They are commonly installed with air source heat pumps, ground source heat pumps, electric boilers, biomass boilers, commercial heating systems and chilled-water applications.

Buffer vessel or buffer tank?

Although the terms “buffer tank” and “buffer vessel” are often used interchangeably, both generally describe an insulated water vessel that sits between the heat source and the heating or cooling distribution system.

What is a buffer tank?

A buffer tank is an insulated vessel containing heating or chilled water. It increases the total water volume within a system and can store a limited amount of thermal energy.

In a heating system, the buffer tank stores the system’s heated water. In a cooling installation, it stores chilled water. The stored water helps stabilise system temperatures and allows the heat source or chiller to operate for longer, more consistent periods.

A buffer tank does not normally heat the water itself. Instead, it stores energy produced by equipment such as a heat pump, boiler or chiller.

What is a buffer vessel?

A buffer vessel performs the same basic function as a buffer tank. The term “vessel” is commonly used in commercial heating and HVAC applications, while “tank” is frequently used in domestic and heat-pump systems.

A buffer vessel should not be confused with an expansion vessel. A buffer vessel stores system water and thermal energy, whereas an expansion vessel accommodates the expansion of water as it heats up.

This Buffer Tanks and Vessels FAQ webpage explains what buffer tanks are, how they work, why they are used, how they are sized and the main differences between buffer vessels, thermal stores and expansion vessels. It also covers their use with heat pumps, boilers, heating systems and cooling applications.