A circulator pump is necessary to circulate water in a hydronic system. Cast iron circulator pumps are typically cheaper than stainless steel or bronze pumps, but can only be used in a closed system. This is because the oxygen in an open system will corrode the cast iron components of the pump. If you are working with an open system, it is suggested that you go with the more durable, though more expensive, stainless steel or bronze pumps.
You can find Taco circulator pumps at www.supplyhouse.com.
