Cast-iron boilers are often a top choice for the military, government institutions, and other applications that require rugged strength. These boilers are known for their heavy-duty build and long service lives, often extending up to 50 years on average. Many models achieve this long duty period thanks to thick heat exchanger walls and a corrosion-resistant design that wards of rust and deterioration. Due to their size and weight, cast-iron units are often created in sections to simplify installation.