GRUNFOS SUPERBRUTE 26-99 3 SPEED

I am placing a Grundfoss 26-99 circ for my boiler storage tank loop and was wondering if I need a cast iron or bronze circ? I was told bronze,but the cast is $150.00 cheaper.

Jim I beleave you are planning a closed loop system ( pressurized ), There for a cast iron pump is all you need . If you had an open system as in some of the outside boilers or if you were useing it for circulating DHW then you would need a bronze or a stainless .