Chemworld Boiler Rust Inhibitor - 1/2 Gallon - Treats up to 250 Gallons of Water Boiler Rust Inhibitor - Treats up to 250 gallons of fresh water Boiler Anti Corrosion Chemical Ideal for outdoor boilers and most closed loop boiler systems. Prevents boiler and piping rust. Safe for use on Copper, Iron, SSTL, PEX and Bronze Metals.