Water Thermal-Expansion Volume
Expanded water volume gained on heating from bundled NIST water-density points.
Example
You enter
- System water volume (gal) 50
- Cold inlet temperature (°F) 50
- Set hot temperature (°F) 140
- System type true
You get
- Expanded volume gained 0.839 gal
- Expansion (% of system) 1.68%
Checked against published worked examples from: NIST / standard steam tables (water density vs. temperature).
Details, formula, and sources
ScopeThe expansion as a percent of system volume, and a closed-system expansion-control note.
Formula or tabledV = V * (rho_cold / rho_hot - 1), where rho is water density (g/mL) at the cold inlet and set hot temperature, interpolated from bundled NIST water-density points within 32-212 F.
Source and editionWater density vs. temperature, NIST / standard steam tables, by name (public domain).
Free accessFree at nist.gov; the density-temperature relation is public.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesvolume_gal, cold_f, hot_f, closed_system, expansion_gal, expansion_pct
- Density range interpolated within 32-212 F; temperatures outside are rejectedNIST water-density table