Expansion Tank Sizing Calculator (Non-Potable)

TO PROPERLY SIZE A WATTS SERIES ETX, ETSX, ETA or ET-RA NON-POTABLE WATER EXPANSION TANK:

Enter the appropriate information in the boxes below

* All Fields Are Required *

System Volume (gallons)

System volume must include the total capacity of the boiler, piping, heat exchangers, radiators, etc.
Fluid Type
Supply Pressure (psi)
The set pressure of the boiler fill valve.
Air Pre-Charge (psi)
12psi Air Charge is Standard.
Relief Valve (psi)
The set pressure of the relief valve.
Initial Temperature - Start (°F)
NOTE: The lowest setting of the aquastat.
Max Temperature - End (°F)
NOTE: The maximum setting of the aquastat.
Expansion Factor
Calculated total volume (gallons)
Calculated acceptance volume (gallons)

WATTS Model Tank Volume
(Gal) 		Tank
Acceptance
(Gal) 		MAX. PRESSURE (PSI)
Model ETX mounts to supply piping » More Info.
Specification Sheet - ETX/ETSX
ETX-15 2.1 1.0 75
ETX-30 4.5 2.5 75
ETX-60 6.0 3.0 75
ETX-90 15.0 6.0 100
Model ETSX is free standing » More Info.
Specification Sheet - ETX/ETSX
ETSX-30 15.0 6.0 100
ETSX-40 20.0 8.0 100
ETSX-60 33.0 13.3 100
ETSX-90 44.0 17.7 100
ETSX-110 62.0 24.9 100
ETSX-160 81.0 32.6 100
ASME Pressurized Expansion Tanks
Fixed Bladder Type » More Info.
Specification Sheet - ETA
ETA-15 7.8 6.3 150
ETA-20 10.9 8.8 150
ETA-40 25 20.2 150
ETA-60 35 28 150
ETA-80 45 36 125
ETA-100 60 48.5 125
ETA-120 70 56.5 125
ETA-144 80 65 125
ETA-180 90 73 125
ETA-200 115 93 125
ETA-240 140 113.5 125
ASME Pressurized Expansion Tanks
Removable Bladder Type » More Info.
Specification Sheet - ET-RA
ET-RA 35 10 10 125
ET-RA 50 13 13 125
ET-RA 85 23 23 125
ET-RA 130 35 35 125
ET-RA 200 53 53 125
ET-RA 300 79 79 125
ET-RA 400 106 106 125
ET-RA 500 132 132 125
ET-RA 600 158 158 125
ET-RA 800 211 211 125
ET-RA 1000 264 264 125
ET-RA 1200 317 317 125
ET-RA 1400 370 370 125
ET-RA 1600 422 422 125
ET-RA 2000 528 528 125
HIDE CHART

How do I size my expansion tank?

  1. Using the calculated acceptance volume and the calculated total volume, select a tank from the chart to the right.
    • Tank volume of the selected="selected" model must be greater than the calculated total volume.
    • Tank acceptance of the selected="selected" model must be greater than the calculated acceptance volume.
    Note: Both the Tank Volume and the Acceptance Volume must be greater than the calculated volumes as indicated.
  2. A pressure reducing valve should be installed on the supply when system pressure exceeds 80psi.
  3. To accommodate the thermal expansion required for higher temperature and/or higher pressure systems, multiple tanks may be used. Please contact the factory for sizing information.
  4. For complex tank sizing for multiple apartments/condos, please contact the factory for sizing information.



IMPORTANT: This Watts thermal expansion tank sizing tool should be used as a general guide to sizing thermal expansion tanks. Sizing calculations are wholly dependent on user input and are therefore only as accurate as the sizing criteria entered by the user. Use of this tool does not constitute a guarantee that the results obtained are suitable for any specific application.

Watts product specifications in U.S. customary units and metric are approximate and are provided for reference only. For precise measurements, please contact Watts Technical Service. Watts reserves the right to change or modify product design, construction, specifications, or materials without prior notice and without incurring any obligation to make such changes and modifications on Watts products previously or subsequently sold.