4.7 gallon, pre-charged expansion tank, for closed loop hydronic piping system 1/2" male pipe thread, used on closed loop hydronic system piping to control thermal expansion of hot water, accepts increased volume of eater created when the system water is heated, steel construction, rugged flexible diaphragm, compact size, compatible with gylcol systems, hydrostatic test pressure 75 PSI, maximum temperature 240&degree. Fahrenheit, maximum pressure 60 PSI, pre-charged at 12 PSI, ETX-30 for use on finned tube baseboard from 25,000 BTU to 150,000 BTU, convectors & unit heaters from 75,000 BTU to up to 100,000 BTU, Cast iron radiators from 50,000 BTU to 100,000 BTU & Cast iron baseboards up to 50,000 BTU net boiler output.