Superior heat transfer properties permit use of smaller, compact cast-iron heat exchanger sections. The flue passage design, thermal pin pattern and consistent wall thickness ensure uniform heat transfer with less thermal strain and metal fatigue. There's a choice made in the manufacturing process that directly affects the vulnerability of boilers to leaks.
Some manufacturers choose to join their cast-iron boiler sections together with elastomer gaskets.
It's a lower cost technique than using metal push nipples. In our computer-assisted manufacturing facility, we machine our sections and push nipples to microscopic tolerances. Then we pull them together under intense pressure. This painstaking process results in a positive, durable seal. The sections and push nipples expand and contract uniformly.