Water Worker pre-charged boiler expansion tank for closed-loop hydronic heating systems using baseboards or radiators. A heavy-duty diaphragm flexes against an air cushion to maintain a safe operating pressure. Maximum temperature of 240 degrees Fahrenheit. Maximum working pressure of 100 PSI. Pre-charged to 12 PSI. 1/2" NPTM. Capacity: 4.4 gallons. Easy to install. Compatible with all types of boiler heating systems. Durable, long-lasting steel tank. Effectively controls system pressure. Heavy-duty diaphragm for long life. Air-tight cushion - factory pre-charged to 12 psig. Maximum working pressure: 100 psig. Maximum operating temperature: 240 degrees Fahrenheit. Boiler BTU Rating: 75,000 to 150,000. 32 ES