Which type of boiler is considered the largest and is built to customer specifications?

The type of boiler that is considered the largest and built to customer specifications is field erected boilers. These boilers are designed and constructed on-site to meet specific requirements set by the customer, which can include dimensions, output capacities, and other operational criteria. The construction process allows for customization that is often necessary for large industrial applications where space and operational needs may vary significantly.

Field erected boilers are typically larger than packaged boilers, which come pre-assembled and are limited in their customization. On the other hand, shop assembled boilers are built in a factory and then shipped, which might limit their size and customization options compared to field erected units. Modular boilers often consist of smaller, pre-fabricated units that can be assembled on-site but do not reach the scale and customization level of field erected boilers.

In summary, field erected boilers are specifically tailored for large-scale applications, ensuring that they meet the unique requirements of the installation site, making them the largest type that is built according to customer specifications.