Expansion Tank Sizing Calculator
Bladder expansion tank volume for a closed hydronic loop from system volume and temperatures.
Water expands ~3% from 4 °C to 80 °C — 15 L in a 500 L system. Precharge the bladder to the fill pressure BEFORE connecting, or the acceptance volume vanishes.
Formula
Note: Expansion fit ±10%; use glycol-corrected tables for antifreeze loops (glycol expands more).
Expansion Tank Sizing Calculator is a free expansion tank size for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Expansion Tank Sizing Calculator
Bladder expansion tank volume for a closed hydronic loop from system volume and temperatures. The calculation implements V_e = V_sys·e(T); V_tank = V_e / (1 − P_fill,abs/P_max,abs) (ASHRAE Handbook — HVAC Systems, ch. 13). Water expands ~3% from 4 °C to 80 °C — 15 L in a 500 L system. Precharge the bladder to the fill pressure BEFORE connecting, or the acceptance volume vanishes.
How to use Expansion Tank Sizing Calculator
- 1Enter System water volume in L (Estimate ~12 L/kW for radiator systems).
- 2Enter Max operating temperature in °C.
- 3Enter Fill (precharge) pressure in kPa(g).
- 4Enter Relief valve setting in kPa(g).
- 5Read Expansion volume, Required tank size instantly — no submit button needed.
- 6Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Expansion Tank Sizing Calculator?
- ✓Implements the standard formula — V_e = V_sys·e(T); V_tank = V_e / (1 − P_fill,abs/P_max,abs)
- ✓Reference cited on-page: ASHRAE Handbook — HVAC Systems, ch. 13
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Expansion Tank Sizing Calculator use?+
It computes V_e = V_sys·e(T); V_tank = V_e / (1 − P_fill,abs/P_max,abs), per ASHRAE Handbook — HVAC Systems, ch. 13. The formula is displayed under the result.
What should I keep in mind when using this calculator?+
Water expands ~3% from 4 °C to 80 °C — 15 L in a 500 L system. Precharge the bladder to the fill pressure BEFORE connecting, or the acceptance volume vanishes. Note: Expansion fit ±10%; use glycol-corrected tables for antifreeze loops (glycol expands more).
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Expansion Tank Sizing Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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