Expansion & materials
Fluid expansion from density change
- where
- expansion volume (L)
- cold system volume (L)
- cold density (kg/m³)
- hot density (kg/m³)
Explain this equation
Works out how much water in a sealed system expands when heated. It is the first step in sizing an expansion vessel.
V_cold is the system volume when cold. ρ_cold and ρ_hot are the fluid densities at the cold fill and maximum working temperatures. V_e is the extra volume the system has to accept.
The mass of water stays the same, so volume is inversely proportional to density. The hot volume is V_cold × ρ_cold / ρ_hot. Taking away the cold volume leaves the expansion.
Sense check: 150 L heated from about 20 °C (998.2 kg/m³) to 80 °C (971.8 kg/m³) expands by about 4.1 L, roughly 2.7%.
Watch out: glycol mixes expand more than plain water. Use the actual fluid's properties at the right temperatures.
Enter your values to see the result.
Good to know
Use verified properties for actual fluid and temperatures. Glycol changes the expansion behaviour.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.