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Sizing an Expansion Tank
You need an expansion tank if you have a closed system. A closed system maintains the same fluid in it at all times. When the water is heated and expands, it needs a place to go, and the expansion tank fills that role. In contrast, an open system has water entering it via the municipal supply and water leaving it via plumbing fixtures. An open boiler (such as an outdoor, non-pressurized wood furnace) is also an open system. If you have a backflow preventer, this creates a closed system and you will need a tank even if you have a direct system.

To size your expansion tank‚ you first need to know how much water is in the system. See below:

Total Length of 1/2"" pipe x .00921 = ______ Gallons
Total Length of 3/4"" pipe x .01837 = ______ Gallons
Total Length of 1"" pipe x .03025 = ______ Gallons
Size of water heater or boiler = ______ Gallons
Total System Volume = _____ X .088
Minimum Expansion Tank Size = _____ Gallons (round up)
Image Model Name Price Add to Cart
det-20-m1.jpg DET-5-M1 Watts 2.1 Gallon Domestic Expansion Tank Price: $88.43
 
et.jpg ETX15 Watts 2.1 Gallon Expansion Tank Price: $29.38
 
et.jpg ETX30 Watts 4.5 Gallon Expansion Tank Price: $39.62
 
et.jpg ETX60 Watts 6 Gallon Expansion Tank Price: $82.50
 
et.jpg ETX90 Watts 15 Gallon Expansion Tank Price: $157.64
 
supervent.bmp PV075 Honeywell 3/4" NPT SuperVent Air Eliminator Price: $79.31
 
supervent.bmp PV100 Honeywell 1" NPT SuperVent Air Eliminator Price: $94.37
 
supervent.bmp PV125 Honeywell 1-1/4" NPT SuperVent Air Eliminator Price: $123.89
 
B911S.jpg B911-M3 Bronze Combination Fill Valve and Backflow Preventers Price: $106.06