System Type
Type of system requiring expansion tank
When Do You Need an Expansion Tank?
- Closed-loop heating systems: Boilers, radiant floors (code required)
- Water heaters: Required in closed water systems with backflow preventers or check valves
- Chilled water systems: Prevents pressure buildup during temperature changes
- Solar thermal: Handles expansion from solar collector heating
System Volume
Total water capacity of entire system
Estimating System Volume:
- Boiler: Check boiler nameplate or manual for water content
- Piping: 1/2" = 0.015 gal/ft, 3/4" = 0.023 gal/ft, 1" = 0.04 gal/ft, 1-1/4" = 0.064 gal/ft
- Baseboard: Typically 0.03-0.05 gallons per foot
- Radiators: Check manufacturer specs (varies widely)
- Quick estimate: Residential systems typically 40-80 gallons total
System Pressures & Temperature
Cold fill pressure (gauge reading)
Pressure relief valve setting (typically 30 PSI)
Average system water temperature
Maximum expected water temperature
Important Pressure Guidelines:
- Fill Pressure: Should be building height ÷ 2.31 + 5 PSI minimum
- Example: 20 ft tall building = (20 ÷ 2.31) + 5 = 13.7 PSI minimum
- Relief Valve: Standard is 30 PSI for residential, 50 PSI for commercial
- Max Pressure: Must be relief valve setting or lower