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Vs = Water Heater Volume + Pipe Volume (≈ 0.04 gal/ft × pipe length)Water expands when heated — expansion tank absorbs volume without relieving via TP valve.
Ve = Vs × (T2 − T1) × β (thermal expansion coefficient ≈ 0.0002/°F × ΔT simplified)Po is precharge pressure; Pmax is max system pressure before relief valve opens.
Acceptance = (Po ÷ (Po − Pmax)) × Ve — select tank with ≥ required acceptanceUpdated: July 2026
System ~55 gal with piping. Standard 2 gal expansion tank typically adequate for residential closed system.
Small heater volume but extensive piping adds system volume — may need larger tank than expected.
Higher precharge needed. Tank acceptance decreases at high pressure — upsize tank model.
Select correct thermal expansion tank size for closed-loop plumbing systems with check valves or PRVs. Enter water heater volume, supply pressure, and temperature rise to calculate required acceptance volume and tank model.