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Expansion Vessel Calculator
Calculate the correct expansion vessel size for sealed heating systems. Enter the system water volume, maximum temperature, and pressures to determine the required vessel capacity.
Why Expansion Vessels Matter
In a sealed heating system, water expands as it heats up. The expansion vessel absorbs this volume increase, preventing the pressure relief valve from discharging water every heating cycle.
An undersized vessel causes frequent pressure relief valve operation, leading to system water loss, corrosion, and the need for regular repressurisation.
Frequently Asked Questions
How do I estimate system water volume?
Count the radiators and pipe lengths. A typical radiator holds 5–10 litres. Add boiler water content (5–15 litres) and pipe volume (0.3 L/m for 22 mm, 0.5 L/m for 28 mm).
What pressure should the vessel pre-charge be?
The vessel pre-charge pressure should equal the cold fill pressure (typically 1.0 bar). Check and adjust the pre-charge when the system is cold and depressurised.
Expansion Vessel Calculator
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